kvm: Note an RCU quiescent state on guest exit

As of today, KVM notes a quiescent state only in guest entry, which is good
as it avoids the guest being interrupted for current RCU operations.

While

kvm: Note an RCU quiescent state on guest exit

As of today, KVM notes a quiescent state only in guest entry, which is good
as it avoids the guest being interrupted for current RCU operations.

While the guest vcpu runs, it can be interrupted by a timer IRQ that will
check for any RCU operations waiting for this CPU. In case there are any of
such, it invokes rcu_core() in order to sched-out the current thread and
note a quiescent state.

This occasional schedule work will introduce tens of microsseconds of
latency, which is really bad for vcpus running latency-sensitive
applications, such as real-time workloads.

So, note a quiescent state in guest exit, so the interrupted guests is able
to deal with any pending RCU operations before being required to invoke
rcu_core(), and thus avoid the overhead of related scheduler work.

Signed-off-by: Leonardo Bras <[email protected]>
Acked-by: Paul E. McKenney <[email protected]>
Acked-by: Sean Christopherson <[email protected]>
Message-ID: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

show more ...

context_tracking, rcu: Rename rcu_dynticks_curr_cpu_in_eqs() into rcu_is_watching_curr_cpu()

The context_tracking.state RCU_DYNTICKS subvariable has been renamed to
RCU_WATCHING, reflect that change

context_tracking, rcu: Rename rcu_dynticks_curr_cpu_in_eqs() into rcu_is_watching_curr_cpu()

The context_tracking.state RCU_DYNTICKS subvariable has been renamed to
RCU_WATCHING, reflect that change in the related helpers.

Note that "watching" is the opposite of "in EQS", so the negation is lifted
out of the helper and into the callsites.

Signed-off-by: Valentin Schneider <[email protected]>
Reviewed-by: Frederic Weisbecker <[email protected]>
Signed-off-by: Neeraj Upadhyay <[email protected]>

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context_tracking, rcu: Rename RCU_DYNTICKS_IDX into CT_RCU_WATCHING

The symbols relating to the CT_STATE part of context_tracking.state are now
all prefixed with CT_STATE.

The RCU dynticks counter

context_tracking, rcu: Rename RCU_DYNTICKS_IDX into CT_RCU_WATCHING

The symbols relating to the CT_STATE part of context_tracking.state are now
all prefixed with CT_STATE.

The RCU dynticks counter part of that atomic variable still involves
symbols with different prefixes, align them all to be prefixed with
CT_RCU_WATCHING.

Suggested-by: "Paul E. McKenney" <[email protected]>
Signed-off-by: Valentin Schneider <[email protected]>
Reviewed-by: Frederic Weisbecker <[email protected]>
Acked-by: Thomas Gleixner <[email protected]>
Signed-off-by: Neeraj Upadhyay <[email protected]>

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treewide: context_tracking: Rename CONTEXT_* into CT_STATE_*

Context tracking state related symbols currently use a mix of the
CONTEXT_ (e.g. CONTEXT_KERNEL) and CT_SATE_ (e.g. CT_STATE_MASK) prefix

treewide: context_tracking: Rename CONTEXT_* into CT_STATE_*

Context tracking state related symbols currently use a mix of the
CONTEXT_ (e.g. CONTEXT_KERNEL) and CT_SATE_ (e.g. CT_STATE_MASK) prefixes.

Clean up the naming and make the ctx_state enum use the CT_STATE_ prefix.

Suggested-by: Frederic Weisbecker <[email protected]>
Signed-off-by: Valentin Schneider <[email protected]>
Acked-by: Frederic Weisbecker <[email protected]>
Acked-by: Thomas Gleixner <[email protected]>
Signed-off-by: Neeraj Upadhyay <[email protected]>

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locking/atomic: treewide: use raw_atomic*_<op>()

Now that we have raw_atomic*_<op>() definitions, there's no need to use
arch_atomic*_<op>() definitions outside of the low-level atomic
definitions.

locking/atomic: treewide: use raw_atomic*_<op>()

Now that we have raw_atomic*_<op>() definitions, there's no need to use
arch_atomic*_<op>() definitions outside of the low-level atomic
definitions.

Move treewide users of arch_atomic*_<op>() over to the equivalent
raw_atomic*_<op>().

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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context_tracking: Fix KCSAN noinstr violation

With KCSAN enabled, even empty inline stubs can be out-of-lined.

Force the context_tracking_guest_exit() stub inline.

Fixes the following warnings:

context_tracking: Fix KCSAN noinstr violation

With KCSAN enabled, even empty inline stubs can be out-of-lined.

Force the context_tracking_guest_exit() stub inline.

Fixes the following warnings:

vmlinux.o: warning: objtool: vmx_vcpu_enter_exit+0x1be: call to context_tracking_guest_exit() leaves .noinstr.text section
vmlinux.o: warning: objtool: svm_vcpu_enter_exit+0x85: call to context_tracking_guest_exit() leaves .noinstr.text section

Signed-off-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lore.kernel.org/r/dc93f45abdec90c171108b4b590b7fff5790963c.1681320026.git.jpoimboe@kernel.org

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entry: Fix noinstr warning in __enter_from_user_mode()

__enter_from_user_mode() is triggering noinstr warnings with
CONFIG_DEBUG_PREEMPT due to its call of preempt_count_add() via
ct_state().

The p

entry: Fix noinstr warning in __enter_from_user_mode()

__enter_from_user_mode() is triggering noinstr warnings with
CONFIG_DEBUG_PREEMPT due to its call of preempt_count_add() via
ct_state().

The preemption disable isn't needed as interrupts are already disabled.
And the context_tracking_enabled() check in ct_state() also isn't needed
as that's already being done by the CT_WARN_ON().

Just use __ct_state() instead.

Fixes the following warnings:

vmlinux.o: warning: objtool: enter_from_user_mode+0xba: call to preempt_count_add() leaves .noinstr.text section
vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0xf9: call to preempt_count_add() leaves .noinstr.text section
vmlinux.o: warning: objtool: syscall_enter_from_user_mode_prepare+0xc7: call to preempt_count_add() leaves .noinstr.text section
vmlinux.o: warning: objtool: irqentry_enter_from_user_mode+0xba: call to preempt_count_add() leaves .noinstr.text section

Fixes: 171476775d32 ("context_tracking: Convert state to atomic_t")
Signed-off-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/d8955fa6d68dc955dda19baf13ae014ae27926f5.1677369694.git.jpoimboe@kernel.org

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cpuidle: lib/bug: Disable rcu_is_watching() during WARN/BUG

In order to avoid WARN/BUG from generating nested or even recursive
warnings, force rcu_is_watching() true during
WARN/lockdep_rcu_suspici

cpuidle: lib/bug: Disable rcu_is_watching() during WARN/BUG

In order to avoid WARN/BUG from generating nested or even recursive
warnings, force rcu_is_watching() true during
WARN/lockdep_rcu_suspicious().

Notably things like unwinding the stack can trigger rcu_dereference()
warnings, which then triggers more unwinding which then triggers more
warnings etc..

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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context_tracking: Convert state to atomic_t

Context tracking's state and dynticks counter are going to be merged
in a single field so that both updates can happen atomically and at the
same time. Pr

context_tracking: Convert state to atomic_t

Context tracking's state and dynticks counter are going to be merged
in a single field so that both updates can happen atomically and at the
same time. Prepare for that with converting the state into an atomic_t.

[ paulmck: Apply kernel test robot feedback. ]

Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Neeraj Upadhyay <[email protected]>
Cc: Uladzislau Rezki <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Nicolas Saenz Julienne <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Xiongfeng Wang <[email protected]>
Cc: Yu Liao <[email protected]>
Cc: Phil Auld <[email protected]>
Cc: Paul Gortmaker<[email protected]>
Cc: Alex Belits <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Reviewed-by: Nicolas Saenz Julienne <[email protected]>
Tested-by: Nicolas Saenz Julienne <[email protected]>

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rcu/context-tracking: Move RCU-dynticks internal functions to context_tracking

Move the core RCU eqs/dynticks functions to context tracking so that
we can later merge all that code within context tr

rcu/context-tracking: Move RCU-dynticks internal functions to context_tracking

Move the core RCU eqs/dynticks functions to context tracking so that
we can later merge all that code within context tracking.

Acked-by: Paul E. McKenney <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Neeraj Upadhyay <[email protected]>
Cc: Uladzislau Rezki <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Nicolas Saenz Julienne <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Xiongfeng Wang <[email protected]>
Cc: Yu Liao <[email protected]>
Cc: Phil Auld <[email protected]>
Cc: Paul Gortmaker<[email protected]>
Cc: Alex Belits <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Reviewed-by: Nicolas Saenz Julienne <[email protected]>
Tested-by: Nicolas Saenz Julienne <[email protected]>

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context_tracking: Take idle eqs entrypoints over RCU

The RCU dynticks counter is going to be merged into the context tracking
subsystem. Start with moving the idle extended quiescent states
entrypoi

context_tracking: Take idle eqs entrypoints over RCU

The RCU dynticks counter is going to be merged into the context tracking
subsystem. Start with moving the idle extended quiescent states
entrypoints to context tracking. For now those are dumb redirections to
existing RCU calls.

[ paulmck: Apply kernel test robot feedback. ]

Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Neeraj Upadhyay <[email protected]>
Cc: Uladzislau Rezki <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Nicolas Saenz Julienne <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Xiongfeng Wang <[email protected]>
Cc: Yu Liao <[email protected]>
Cc: Phil Auld <[email protected]>
Cc: Paul Gortmaker<[email protected]>
Cc: Alex Belits <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Reviewed-by: Nicolas Saenz Julienne <[email protected]>
Tested-by: Nicolas Saenz Julienne <[email protected]>

show more ...

context_tracking: Split user tracking Kconfig

Context tracking is going to be used not only to track user transitions
but also idle/IRQs/NMIs. The user tracking part will then become a
separate feat

context_tracking: Split user tracking Kconfig

Context tracking is going to be used not only to track user transitions
but also idle/IRQs/NMIs. The user tracking part will then become a
separate feature. Prepare Kconfig for that.

[ frederic: Apply Max Filippov feedback. ]

Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Neeraj Upadhyay <[email protected]>
Cc: Uladzislau Rezki <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Nicolas Saenz Julienne <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Xiongfeng Wang <[email protected]>
Cc: Yu Liao <[email protected]>
Cc: Phil Auld <[email protected]>
Cc: Paul Gortmaker<[email protected]>
Cc: Alex Belits <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Reviewed-by: Nicolas Saenz Julienne <[email protected]>
Tested-by: Nicolas Saenz Julienne <[email protected]>

show more ...

context_tracking: Rename context_tracking_cpu_set() to ct_cpu_track_user()

context_tracking_cpu_set() is called in order to tell a CPU to track
user/kernel transitions. Since context tracking is goi

context_tracking: Rename context_tracking_cpu_set() to ct_cpu_track_user()

context_tracking_cpu_set() is called in order to tell a CPU to track
user/kernel transitions. Since context tracking is going to expand in
to also track transitions from/to idle/IRQ/NMIs, the scope
of this function name becomes too broad and needs to be made more
specific. Also shorten the prefix to align with the new namespace.

Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Neeraj Upadhyay <[email protected]>
Cc: Uladzislau Rezki <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Nicolas Saenz Julienne <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Xiongfeng Wang <[email protected]>
Cc: Yu Liao <[email protected]>
Cc: Phil Auld <[email protected]>
Cc: Paul Gortmaker<[email protected]>
Cc: Alex Belits <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Reviewed-by: Nicolas Saenz Julienne <[email protected]>
Tested-by: Nicolas Saenz Julienne <[email protected]>

show more ...

context_tracking: Rename context_tracking_enter/exit() to ct_user_enter/exit()

context_tracking_enter() and context_tracking_exit() have confusing
names that don't explain the fact they are referrin

context_tracking: Rename context_tracking_enter/exit() to ct_user_enter/exit()

context_tracking_enter() and context_tracking_exit() have confusing
names that don't explain the fact they are referring to user/guest state.

Use more self-explanatory names and shrink to the new context tracking
prefix instead.

Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Neeraj Upadhyay <[email protected]>
Cc: Uladzislau Rezki <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Nicolas Saenz Julienne <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Xiongfeng Wang <[email protected]>
Cc: Yu Liao <[email protected]>
Cc: Phil Auld <[email protected]>
Cc: Paul Gortmaker<[email protected]>
Cc: Alex Belits <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Reviewed-by: Nicolas Saenz Julienne <[email protected]>
Tested-by: Nicolas Saenz Julienne <[email protected]>

show more ...

context_tracking: Rename context_tracking_user_enter/exit() to user_enter/exit_callable()

context_tracking_user_enter() and context_tracking_user_exit() are
ASM callable versions of user_enter() and

context_tracking: Rename context_tracking_user_enter/exit() to user_enter/exit_callable()

context_tracking_user_enter() and context_tracking_user_exit() are
ASM callable versions of user_enter() and user_exit() for architectures
that didn't manage to check the context tracking static key from ASM.
Change those function names to better reflect their purpose.

[ frederic: Apply Max Filippov feedback. ]

Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Neeraj Upadhyay <[email protected]>
Cc: Uladzislau Rezki <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Nicolas Saenz Julienne <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Xiongfeng Wang <[email protected]>
Cc: Yu Liao <[email protected]>
Cc: Phil Auld <[email protected]>
Cc: Paul Gortmaker<[email protected]>
Cc: Alex Belits <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Reviewed-by: Nicolas Saenz Julienne <[email protected]>
Tested-by: Nicolas Saenz Julienne <[email protected]>

show more ...

context_tracking: Rename __context_tracking_enter/exit() to __ct_user_enter/exit()

The context tracking namespace is going to expand and some new functions
will require even longer names. Start shri

context_tracking: Rename __context_tracking_enter/exit() to __ct_user_enter/exit()

The context tracking namespace is going to expand and some new functions
will require even longer names. Start shrinking the context_tracking
prefix to "ct" as is already the case for some existing macros, this
will make the introduction of new functions easier.

Acked-by: Paul E. McKenney <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Neeraj Upadhyay <[email protected]>
Cc: Uladzislau Rezki <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Nicolas Saenz Julienne <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Xiongfeng Wang <[email protected]>
Cc: Yu Liao <[email protected]>
Cc: Phil Auld <[email protected]>
Cc: Paul Gortmaker<[email protected]>
Cc: Alex Belits <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Reviewed-by: Nicolas Saenz Julienne <[email protected]>
Tested-by: Nicolas Saenz Julienne <[email protected]>

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x86: Always inline context_tracking_guest_enter()

Yes, it really did out-of-line this....

vmlinux.o: warning: objtool: vmx_vcpu_enter_exit()+0x31: call to context_tracking_guest_enter() leaves .noi

x86: Always inline context_tracking_guest_enter()

Yes, it really did out-of-line this....

vmlinux.o: warning: objtool: vmx_vcpu_enter_exit()+0x31: call to context_tracking_guest_enter() leaves .noinstr.text section

000000000019f660 <context_tracking_guest_enter>:
19f660: e8 00 00 00 00 callq 19f665 <context_tracking_guest_enter+0x5> 19f661: R_X86_64_PLT32 __sanitizer_cov_trace_pc-0x4
19f665: 31 c0 xor %eax,%eax
19f667: c3 retq

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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context_tracking: KVM: Move guest enter/exit wrappers to KVM's domain

Move the guest enter/exit wrappers to kvm_host.h so that KVM can manage
its context tracking vs. vtime accounting without bleedi

context_tracking: KVM: Move guest enter/exit wrappers to KVM's domain

Move the guest enter/exit wrappers to kvm_host.h so that KVM can manage
its context tracking vs. vtime accounting without bleeding too many KVM
details into the context tracking code.

No functional change intended.

Signed-off-by: Sean Christopherson <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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context_tracking: Consolidate guest enter/exit wrappers

Consolidate the guest enter/exit wrappers, providing and tweaking stubs
as needed. This will allow moving the wrappers under KVM without havi

context_tracking: Consolidate guest enter/exit wrappers

Consolidate the guest enter/exit wrappers, providing and tweaking stubs
as needed. This will allow moving the wrappers under KVM without having
to bleed #ifdefs into the soon-to-be KVM code.

No functional change intended.

Signed-off-by: Sean Christopherson <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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sched/vtime: Move guest enter/exit vtime accounting to vtime.h

Provide separate helpers for guest enter vtime accounting (in addition to
the existing guest exit helpers), and move all vtime accounti

sched/vtime: Move guest enter/exit vtime accounting to vtime.h

Provide separate helpers for guest enter vtime accounting (in addition to
the existing guest exit helpers), and move all vtime accounting helpers
to vtime.h where the existing #ifdef infrastructure can be leveraged to
better delineate the different types of accounting. This will also allow
future cleanups via deduplication of context tracking code.

Opportunstically delete the vtime_account_kernel() stub now that all
callers are wrapped with CONFIG_VIRT_CPU_ACCOUNTING_NATIVE=y.

No functional change intended.

Signed-off-by: Sean Christopherson <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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context_tracking: Move guest exit vtime accounting to separate helpers

Provide separate vtime accounting functions for guest exit instead of
open coding the logic within the context tracking code.

context_tracking: Move guest exit vtime accounting to separate helpers

Provide separate vtime accounting functions for guest exit instead of
open coding the logic within the context tracking code. This will allow
KVM x86 to handle vtime accounting slightly differently when using
tick-based accounting.

Suggested-by: Thomas Gleixner <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
Co-developed-by: Sean Christopherson <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Christian Borntraeger <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

show more ...

context_tracking: Move guest exit context tracking to separate helpers

Provide separate context tracking helpers for guest exit, the standalone
helpers will be called separately by KVM x86 in later

context_tracking: Move guest exit context tracking to separate helpers

Provide separate context tracking helpers for guest exit, the standalone
helpers will be called separately by KVM x86 in later patches to fix
tick-based accounting.

Suggested-by: Thomas Gleixner <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
Co-developed-by: Sean Christopherson <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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context_tracking: Don't implement exception_enter/exit() on CONFIG_HAVE_CONTEXT_TRACKING_OFFSTACK

The typical steps with context tracking are:

1) Task runs in userspace
2) Task enters the kernel (s

context_tracking: Don't implement exception_enter/exit() on CONFIG_HAVE_CONTEXT_TRACKING_OFFSTACK

The typical steps with context tracking are:

1) Task runs in userspace
2) Task enters the kernel (syscall/exception/IRQ)
3) Task switches from context tracking state CONTEXT_USER to
CONTEXT_KERNEL (user_exit())
4) Task does stuff in kernel
5) Task switches from context tracking state CONTEXT_KERNEL to
CONTEXT_USER (user_enter())
6) Task exits the kernel

If an exception fires between 5) and 6), the pt_regs and the context
tracking disagree on the context of the faulted/trapped instruction.
CONTEXT_KERNEL must be set before the exception handler, that's
unconditional for those handlers that want to be able to call into
schedule(), but CONTEXT_USER must be restored when the exception exits
whereas pt_regs tells that we are resuming to kernel space.

This can't be fixed with storing the context tracking state in a per-cpu
or per-task variable since another exception may fire onto the current
one and overwrite the saved state. Also the task can schedule. So it
has to be stored in a per task stack.

This is how exception_enter()/exception_exit() paper over the problem:

5) Task switches from context tracking state CONTEXT_KERNEL to
CONTEXT_USER (user_enter())
5.1) Exception fires
5.2) prev_state = exception_enter() // save CONTEXT_USER to prev_state
// and set CONTEXT_KERNEL
5.3) Exception handler
5.4) exception_enter(prev_state) // restore CONTEXT_USER
5.5) Exception resumes
6) Task exits the kernel

The condition to live without exception_enter()/exception_exit() is to
forbid exceptions and IRQs between 2) and 3) and between 5) and 6), or if
any is allowed to trigger, it won't call into context tracking, eg: NMIs,
and it won't schedule. These requirements are met by architectures
supporting CONFIG_HAVE_CONTEXT_TRACKING_OFFSTACK and those can
therefore afford not to implement this hack.

Signed-off-by: Frederic Weisbecker <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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compiler.h: Move instrumentation_begin()/end() to new <linux/instrumentation.h> header

Linus pointed out that compiler.h - which is a key header that gets included in every
single one of the 28,000+

compiler.h: Move instrumentation_begin()/end() to new <linux/instrumentation.h> header

Linus pointed out that compiler.h - which is a key header that gets included in every
single one of the 28,000+ kernel files during a kernel build - was bloated in:

655389666643: ("vmlinux.lds.h: Create section for protection against instrumentation")

Linus noted:

> I have pulled this, but do we really want to add this to a header file
> that is _so_ core that it gets included for basically every single
> file built?
>
> I don't even see those instrumentation_begin/end() things used
> anywhere right now.
>
> It seems excessive. That 53 lines is maybe not a lot, but it pushed
> that header file to over 12kB, and while it's mostly comments, it's
> extra IO and parsing basically for _every_ single file compiled in the
> kernel.
>
> For what appears to be absolutely zero upside right now, and I really
> don't see why this should be in such a core header file!

Move these primitives into a new header: <linux/instrumentation.h>, and include that
header in the headers that make use of it.

Unfortunately one of these headers is asm-generic/bug.h, which does get included
in a lot of places, similarly to compiler.h. So the de-bloating effect isn't as
good as we'd like it to be - but at least the interfaces are defined separately.

No change to functionality intended.

Reported-by: Linus Torvalds <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Cc: Thomas Gleixner <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Peter Zijlstra <[email protected]>

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context_tracking: Ensure that the critical path cannot be instrumented

context tracking lacks a few protection mechanisms against instrumentation:

- While the core functions are marked NOKPROBE th

context_tracking: Ensure that the critical path cannot be instrumented

context tracking lacks a few protection mechanisms against instrumentation:

- While the core functions are marked NOKPROBE they lack protection
against function tracing which is required as the function entry/exit
points can be utilized by BPF.

- static functions invoked from the protected functions need to be marked
as well as they can be instrumented otherwise.

- using plain inline allows the compiler to emit traceable and probable
functions.

Fix this by marking the functions noinstr and converting the plain inlines
to __always_inline.

The NOKPROBE_SYMBOL() annotations are removed as the .noinstr.text section
is already excluded from being probed.

Cures the following objtool warnings:

vmlinux.o: warning: objtool: enter_from_user_mode()+0x34: call to __context_tracking_exit() leaves .noinstr.text section
vmlinux.o: warning: objtool: prepare_exit_to_usermode()+0x29: call to __context_tracking_enter() leaves .noinstr.text section
vmlinux.o: warning: objtool: syscall_return_slowpath()+0x29: call to __context_tracking_enter() leaves .noinstr.text section
vmlinux.o: warning: objtool: do_syscall_64()+0x7f: call to __context_tracking_enter() leaves .noinstr.text section
vmlinux.o: warning: objtool: do_int80_syscall_32()+0x3d: call to __context_tracking_enter() leaves .noinstr.text section
vmlinux.o: warning: objtool: do_fast_syscall_32()+0x9c: call to __context_tracking_enter() leaves .noinstr.text section

and generates new ones...

Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Masami Hiramatsu <[email protected]>
Reviewed-by: Alexandre Chartre <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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