KVM: selftests: Define _GNU_SOURCE for all selftests code

Define _GNU_SOURCE is the base CFLAGS instead of relying on selftests to
manually #define _GNU_SOURCE, which is repetitive and error prone.

KVM: selftests: Define _GNU_SOURCE for all selftests code

Define _GNU_SOURCE is the base CFLAGS instead of relying on selftests to
manually #define _GNU_SOURCE, which is repetitive and error prone. E.g.
kselftest_harness.h requires _GNU_SOURCE for asprintf(), but if a selftest
includes kvm_test_harness.h after stdio.h, the include guards result in
the effective version of stdio.h consumed by kvm_test_harness.h not
defining asprintf():

In file included from x86_64/fix_hypercall_test.c:12:
In file included from include/kvm_test_harness.h:11:
../kselftest_harness.h:1169:2: error: call to undeclared function
'asprintf'; ISO C99 and later do not support implicit function declarations
[-Wimplicit-function-declaration]
1169 | asprintf(&test_name, "%s%s%s.%s", f->name,
| ^

When including the rseq selftest's "library" code, #undef _GNU_SOURCE so
that rseq.c controls whether or not it wants to build with _GNU_SOURCE.

Reported-by: Muhammad Usama Anjum <[email protected]>
Acked-by: Claudio Imbrenda <[email protected]>
Acked-by: Oliver Upton <[email protected]>
Acked-by: Anup Patel <[email protected]>
Reviewed-by: Muhammad Usama Anjum <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>

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KVM: selftests: Allow many vCPUs and reader threads per UFFD in demand paging test

At the moment, demand_paging_test does not support profiling/testing
multiple vCPU threads concurrently faulting on

KVM: selftests: Allow many vCPUs and reader threads per UFFD in demand paging test

At the moment, demand_paging_test does not support profiling/testing
multiple vCPU threads concurrently faulting on a single uffd because

(a) "-u" (run test in userfaultfd mode) creates a uffd for each vCPU's
region, so that each uffd services a single vCPU thread.
(b) "-u -o" (userfaultfd mode + overlapped vCPU memory accesses)
simply doesn't work: the test tries to register the same memory
to multiple uffds, causing an error.

Add support for many vcpus per uffd by
(1) Keeping "-u" behavior unchanged.
(2) Making "-u -a" create a single uffd for all of guest memory.
(3) Making "-u -o" implicitly pass "-a", solving the problem in (b).
In cases (2) and (3) all vCPU threads fault on a single uffd.

With potentially multiple vCPUs per UFFD, it makes sense to allow
configuring the number of reader threads per UFFD as well: add the "-r"
flag to do so.

Signed-off-by: Anish Moorthy <[email protected]>
Acked-by: James Houghton <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[sean: fix kernel style violations, use calloc() for arrays]
Signed-off-by: Sean Christopherson <[email protected]>

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KVM: selftests: Add a userfaultfd library

Move the generic userfaultfd code out of demand_paging_test.c into a
common library, userfaultfd_util. This library consists of a setup and a
stop function.

KVM: selftests: Add a userfaultfd library

Move the generic userfaultfd code out of demand_paging_test.c into a
common library, userfaultfd_util. This library consists of a setup and a
stop function. The setup function starts a thread for handling page
faults using the handler callback function. This setup returns a
uffd_desc object which is then used in the stop function (to wait and
destroy the threads).

Reviewed-by: Oliver Upton <[email protected]>
Reviewed-by: Ben Gardon <[email protected]>
Signed-off-by: Ricardo Koller <[email protected]>
Signed-off-by: Marc Zyngier <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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