KVM: x86/mmu: Use high bits for host/mmu writable masks for EPT SPTEs

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Use bits 57 and 58 for HOST_WRITABLE and MMU_WRITABLE when using EPT.
This will allow using bit 11 as a constant MMU_PRESENT, which is
desirable as checking for a shadow-present SPTE is one of the most
common SPTE operations in KVM, particular in hot paths such as page
faults.

EPT is short on low available bits; currently only bit 11 is the only
always-available bit.  Bit 10 is also available, but only while KVM
doesn't support mode-based execution.  On the other hand, PAE paging
doesn't have _any_ high available bits.  Thus, using bit 11 is the only
feasible option for MMU_PRESENT.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210225204749.1512652-20-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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Sean Christopherson 2021-02-25 12:47:44 -08:00 • committed by Paolo Bonzini

parent 5fc3424f8b

commit 613a3f3797

2 changed files with 36 additions and 15 deletions

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arch/x86/kvm/mmu/spte.c

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48

arch/x86/kvm/mmu/spte.h

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