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