From fd717f11015f673487ffc826e59b2bad69d20fe5 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Tue, 7 Jul 2015 14:38:13 +0200 Subject: [PATCH] KVM: x86: apply guest MTRR virtualization on host reserved pages Currently guest MTRR is avoided if kvm_is_reserved_pfn returns true. However, the guest could prefer a different page type than UC for such pages. A good example is that pass-throughed VGA frame buffer is not always UC as host expected. This patch enables full use of virtual guest MTRRs. Suggested-by: Xiao Guangrong Tested-by: Joerg Roedel (on AMD) Signed-off-by: Paolo Bonzini --- arch/x86/kvm/svm.c | 7 ++----- arch/x86/kvm/vmx.c | 11 +++-------- 2 files changed, 5 insertions(+), 13 deletions(-) diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index d36cfaf5a97a..bbc678a66b18 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -1166,14 +1166,11 @@ static u64 svm_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio) u8 mtrr; /* - * 1. MMIO: always map as UC + * 1. MMIO: trust guest MTRR, so same as item 3. * 2. No passthrough: always map as WB, and force guest PAT to WB as well * 3. Passthrough: can't guarantee the result, try to trust guest. */ - if (is_mmio) - return _PAGE_NOCACHE; - - if (!kvm_arch_has_assigned_device(vcpu->kvm)) + if (!is_mmio && !kvm_arch_has_assigned_device(vcpu->kvm)) return 0; mtrr = kvm_mtrr_get_guest_memory_type(vcpu, gfn); diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index e856dd566f4c..5b4e9384717a 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -8632,22 +8632,17 @@ static u64 vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio) u64 ipat = 0; /* For VT-d and EPT combination - * 1. MMIO: always map as UC + * 1. MMIO: guest may want to apply WC, trust it. * 2. EPT with VT-d: * a. VT-d without snooping control feature: can't guarantee the - * result, try to trust guest. + * result, try to trust guest. So the same as item 1. * b. VT-d with snooping control feature: snooping control feature of * VT-d engine can guarantee the cache correctness. Just set it * to WB to keep consistent with host. So the same as item 3. * 3. EPT without VT-d: always map as WB and set IPAT=1 to keep * consistent with host MTRR */ - if (is_mmio) { - cache = MTRR_TYPE_UNCACHABLE; - goto exit; - } - - if (!kvm_arch_has_noncoherent_dma(vcpu->kvm)) { + if (!is_mmio && !kvm_arch_has_noncoherent_dma(vcpu->kvm)) { ipat = VMX_EPT_IPAT_BIT; cache = MTRR_TYPE_WRBACK; goto exit; -- GitLab