| Message ID | 20200213213036.207625-2-olvaffe@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86: honor guest memory type | expand |
On 13/02/20 22:30, Chia-I Wu wrote: > Better reflect the structure of the code and metion why we could not > always honor the guest. > > Signed-off-by: Chia-I Wu <olvaffe@gmail.com> > Cc: Gurchetan Singh <gurchetansingh@chromium.org> > Cc: Gerd Hoffmann <kraxel@redhat.com> > --- > arch/x86/kvm/vmx/vmx.c | 27 +++++++++++++++++---------- > 1 file changed, 17 insertions(+), 10 deletions(-) > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 3be25ecae145..266ef87042da 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -6854,17 +6854,24 @@ static u64 vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio) > u8 cache; > u64 ipat = 0; > > - /* For VT-d and EPT combination > - * 1. MMIO: always map as UC > - * 2. EPT with VT-d: > - * a. VT-d without snooping control feature: can't guarantee the > - * result, try to trust guest. > - * 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 > + /* We wanted to honor guest CD/MTRR/PAT, but doing so could result in > + * memory aliases with conflicting memory types and sometimes MCEs. > + * We have to be careful as to what are honored and when. > + * > + * For MMIO, guest CD/MTRR are ignored. The EPT memory type is set to > + * UC. The effective memory type is UC or WC depending on guest PAT. > + * This was historically the source of MCEs and we want to be > + * conservative. > + * > + * When there is no need to deal with noncoherent DMA (e.g., no VT-d > + * or VT-d has snoop control), guest CD/MTRR/PAT are all ignored. The > + * EPT memory type is set to WB. The effective memory type is forced > + * WB. > + * > + * Otherwise, we trust guest. Guest CD/MTRR/PAT are all honored. The > + * EPT memory type is used to emulate guest CD/MTRR. > */ > + > if (is_mmio) { > cache = MTRR_TYPE_UNCACHABLE; > goto exit; > This is certainly an improvement, especially the part that points out how guest PAT still allows MMIO to be handled as WC. Thanks, Paolo
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 3be25ecae145..266ef87042da 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6854,17 +6854,24 @@ static u64 vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio) u8 cache; u64 ipat = 0; - /* For VT-d and EPT combination - * 1. MMIO: always map as UC - * 2. EPT with VT-d: - * a. VT-d without snooping control feature: can't guarantee the - * result, try to trust guest. - * 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 + /* We wanted to honor guest CD/MTRR/PAT, but doing so could result in + * memory aliases with conflicting memory types and sometimes MCEs. + * We have to be careful as to what are honored and when. + * + * For MMIO, guest CD/MTRR are ignored. The EPT memory type is set to + * UC. The effective memory type is UC or WC depending on guest PAT. + * This was historically the source of MCEs and we want to be + * conservative. + * + * When there is no need to deal with noncoherent DMA (e.g., no VT-d + * or VT-d has snoop control), guest CD/MTRR/PAT are all ignored. The + * EPT memory type is set to WB. The effective memory type is forced + * WB. + * + * Otherwise, we trust guest. Guest CD/MTRR/PAT are all honored. The + * EPT memory type is used to emulate guest CD/MTRR. */ + if (is_mmio) { cache = MTRR_TYPE_UNCACHABLE; goto exit;
Better reflect the structure of the code and metion why we could not always honor the guest. Signed-off-by: Chia-I Wu <olvaffe@gmail.com> Cc: Gurchetan Singh <gurchetansingh@chromium.org> Cc: Gerd Hoffmann <kraxel@redhat.com> --- arch/x86/kvm/vmx/vmx.c | 27 +++++++++++++++++---------- 1 file changed, 17 insertions(+), 10 deletions(-)