KVM: x86/mmu: Use enable_mmio_caching to track if MMIO caching is enabled

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Clear enable_mmio_caching if hardware can't support MMIO caching and use
the dedicated flag to detect if MMIO caching is enabled instead of
assuming shadow_mmio_value==0 means MMIO caching is disabled.  TDX will
use a zero value even when caching is enabled, and is_mmio_spte() isn't
so hot that it needs to avoid an extra memory access, i.e. there's no
reason to be super clever.  And the clever approach may not even be more
performant, e.g. gcc-11 lands the extra check on a non-zero value inline,
but puts the enable_mmio_caching out-of-line, i.e. avoids the few extra
uops for non-MMIO SPTEs.

Cc: Isaku Yamahata <isaku.yamahata@intel.com>
Cc: Kai Huang <kai.huang@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220420002747.3287931-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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Sean Christopherson 2022-04-20 00:27:47 +00:00 • committed by Paolo Bonzini

parent 65936229d3

commit 8b9e74bfbf

3 changed files with 8 additions and 3 deletions

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2

arch/x86/kvm/mmu/mmu.c

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5

arch/x86/kvm/mmu/spte.c

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arch/x86/kvm/mmu/spte.h

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