Commit 1affe455 authored by Yan Zhao's avatar Yan Zhao Committed by Sean Christopherson
Browse files

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



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: default avatarSean Christopherson <seanjc@google.com>
Signed-off-by: default avatarYan 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: default avatarSean Christopherson <seanjc@google.com>
parent 5804c19b

arch/x86/kvm/mmu.h

+7 −0
Original line number Diff line number Diff line
@@ -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);

arch/x86/kvm/mmu/mmu.c

+16 −9
Original line number Diff line number Diff line
@@ -4479,21 +4479,28 @@ static int kvm_tdp_mmu_page_fault(struct kvm_vcpu *vcpu, 
}

#endif



int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)

bool __kvm_mmu_honors_guest_mtrrs(bool vm_has_noncoherent_dma)

{

	/*

	 * 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.

	 * 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.

	 */

	if (shadow_memtype_mask && kvm_arch_has_noncoherent_dma(vcpu->kvm)) {

	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 (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,