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KVM: x86/mmu: Add helpers to return if KVM honors guest MTRRs

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Add helpers to check if KVM honors guest MTRRs instead of open coding the
logic in kvm_tdp_page_fault().  Future fixes and cleanups will also need
to determine if KVM should honor guest MTRRs, e.g. for CR0.CD toggling and
and non-coherent DMA transitions.

Provide an inner helper, __kvm_mmu_honors_guest_mtrrs(), so that KVM can
check if guest MTRRs were honored when stopping non-coherent DMA.

Note, there is no need to explicitly check that TDP is enabled, KVM clears
shadow_memtype_mask when TDP is disabled, i.e. it's non-zero if and only
if EPT is enabled.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Link: https://lore.kernel.org/r/20230714065006.20201-1-yan.y.zhao@intel.com
Link: https://lore.kernel.org/r/20230714065043.20258-1-yan.y.zhao@intel.com
[sean: squash into a one patch, drop explicit TDP check massage changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Yan Zhao 2023-07-14 14:50:06 +08:00 committed by Sean Christopherson
parent 5804c19b80
commit 1affe455d6
2 changed files with 23 additions and 9 deletions
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7
arch/x86/kvm/mmu.h
View File

@ -237,6 +237,13 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
return -(u32)fault & errcode;
}
bool __kvm_mmu_honors_guest_mtrrs(bool vm_has_noncoherent_dma);
static inline bool kvm_mmu_honors_guest_mtrrs(struct kvm *kvm)
{
return __kvm_mmu_honors_guest_mtrrs(kvm_arch_has_noncoherent_dma(kvm));
}
void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end);
int kvm_arch_write_log_dirty(struct kvm_vcpu *vcpu);

25
arch/x86/kvm/mmu/mmu.c
View File

@ -4479,21 +4479,28 @@ out_unlock:
}
#endif
bool __kvm_mmu_honors_guest_mtrrs(bool vm_has_noncoherent_dma)
{
/*
* If host MTRRs are ignored (shadow_memtype_mask is non-zero), and the
* VM has non-coherent DMA (DMA doesn't snoop CPU caches), KVM's ABI is
* to honor the memtype from the guest's MTRRs so that guest accesses
* to memory that is DMA'd aren't cached against the guest's wishes.
*
* Note, KVM may still ultimately ignore guest MTRRs for certain PFNs,
* e.g. KVM will force UC memtype for host MMIO.
*/
return vm_has_noncoherent_dma && shadow_memtype_mask;
}
int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
{
/*
* If the guest's MTRRs may be used to compute the "real" memtype,
* restrict the mapping level to ensure KVM uses a consistent memtype
* across the entire mapping. If the host MTRRs are ignored by TDP
* (shadow_memtype_mask is non-zero), and the VM has non-coherent DMA
* (DMA doesn't snoop CPU caches), KVM's ABI is to honor the memtype
* from the guest's MTRRs so that guest accesses to memory that is
* DMA'd aren't cached against the guest's wishes.
*
* Note, KVM may still ultimately ignore guest MTRRs for certain PFNs,
* e.g. KVM will force UC memtype for host MMIO.
* across the entire mapping.
*/
if (shadow_memtype_mask && kvm_arch_has_noncoherent_dma(vcpu->kvm)) {
if (kvm_mmu_honors_guest_mtrrs(vcpu->kvm)) {
for ( ; fault->max_level > PG_LEVEL_4K; --fault->max_level) {
int page_num = KVM_PAGES_PER_HPAGE(fault->max_level);
gfn_t base = gfn_round_for_level(fault->gfn,