x86/sev: Make sure pages are not skipped during kdump

When shared pages are being converted to private during kdump, additional
checks are performed. They include handling the case of a GHCB page be

x86/sev: Make sure pages are not skipped during kdump

When shared pages are being converted to private during kdump, additional
checks are performed. They include handling the case of a GHCB page being
contained within a huge page.

Currently, this check incorrectly skips a page just below the GHCB page from
being transitioned back to private during kdump preparation.

This skipped page causes a 0x404 #VC exception when it is accessed later while
dumping guest memory for vmcore generation.

Correct the range to be checked for GHCB contained in a huge page. Also,
ensure that the skipped huge page containing the GHCB page is transitioned
back to private by applying the correct address mask later when changing GHCBs
to private at end of kdump preparation.

[ bp: Massage commit message. ]

Fixes: 3074152e56c9 ("x86/sev: Convert shared memory back to private on kexec")
Signed-off-by: Ashish Kalra <[email protected]>
Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Reviewed-by: Tom Lendacky <[email protected]>
Tested-by: Srikanth Aithal <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/[email protected]

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x86/sev: Do not touch VMSA pages during SNP guest memory kdump

When kdump is running makedumpfile to generate vmcore and dump SNP guest
memory it touches the VMSA page of the vCPU executing kdump.

x86/sev: Do not touch VMSA pages during SNP guest memory kdump

When kdump is running makedumpfile to generate vmcore and dump SNP guest
memory it touches the VMSA page of the vCPU executing kdump.

It then results in unrecoverable #NPF/RMP faults as the VMSA page is
marked busy/in-use when the vCPU is running and subsequently a causes
guest softlockup/hang.

Additionally, other APs may be halted in guest mode and their VMSA pages
are marked busy and touching these VMSA pages during guest memory dump
will also cause #NPF.

Issue AP_DESTROY GHCB calls on other APs to ensure they are kicked out
of guest mode and then clear the VMSA bit on their VMSA pages.

If the vCPU running kdump is an AP, mark it's VMSA page as offline to
ensure that makedumpfile excludes that page while dumping guest memory.

Fixes: 3074152e56c9 ("x86/sev: Convert shared memory back to private on kexec")
Signed-off-by: Ashish Kalra <[email protected]>
Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Reviewed-by: Pankaj Gupta <[email protected]>
Reviewed-by: Tom Lendacky <[email protected]>
Tested-by: Srikanth Aithal <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/[email protected]

show more ...