KVM: x86/mmu: Use Accessed bit even when _hardware_ A/D bits are disabled

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Use the Accessed bit in SPTEs even when A/D bits are disabled in hardware,
i.e. propagate accessed information to SPTE.Accessed even when KVM is
doing manual tracking by making SPTEs not-present.  In addition to
eliminating a small amount of code in is_accessed_spte(), this also paves
the way for preserving Accessed information when a SPTE is zapped in
response to a mmu_notifier PROTECTION event, e.g. if a SPTE is zapped
because NUMA balancing kicks in.

Note, EPT is the only flavor of paging in which A/D bits are conditionally
enabled, and the Accessed (and Dirty) bit is software-available when A/D
bits are disabled.

Note #2, there are currently no concrete plans to preserve Accessed
information.  Explorations on that front were the initial catalyst, but
the cleanup is the motivation for the actual commit.

Link: https://lore.kernel.org/r/20241011021051.1557902-13-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

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This commit is contained in:

Sean Christopherson 2024-10-10 19:10:44 -07:00

parent 53510b9125

commit 7971801b56

3 changed files with 5 additions and 13 deletions

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3

arch/x86/kvm/mmu/mmu.c

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4

arch/x86/kvm/mmu/spte.c

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11

arch/x86/kvm/mmu/spte.h

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