On 2024/3/12 00:20, Sean Christopherson wrote: > On Mon, Mar 11, 2024, francisco_flynn wrote: >> when doing kvm_tdp_mmu_map for WC memory, such as pages >> allocated by amdgpu ttm driver for ttm_write_combined >> caching mode(e.g. host coherent in vulkan), >> the spte would be set to WB, in this case, vcpu write >> to these pages would goes to cache first, and never >> be write-combined and host-coherent anymore. so >> WC memory should be treated as MMIO, and the effective >> memory type is depending on guest PAT. > > No, the effective memtype is not fully guest controlled. By forcing the EPT memtype > to UC, the guest can only use UC or WC. I don't know if there's a use case for Well,it's actually the host mapping memory WC and guest uses WC, one use case is virtio-gpu host blob, which is to map physical GPU buffers into guest > the host mapping memory WC while the guest uses WB, but it should be a moot point, > because this this series should do what you want (allow guest to map GPU buffers > as WC). > > https://lore.kernel.org/all/20240309010929.1403984-1-seanjc@xxxxxxxxxx > yes, this is what i want, but for virtio-gpu device, if we mapping WC typed GPU buffer into guest, kvm_arch_has_noncoherent_dma would return false, so on cpu without self-snoop support, guest PAT will be ignored, the effective memory type would be set to WB, causing data inconsistency. + if (!static_cpu_has(X86_FEATURE_SELFSNOOP) && + !kvm_arch_has_noncoherent_dma(vcpu->kvm)) return (MTRR_TYPE_WRBACK << VMX_EPT_MT_EPTE_SHIFT) | VMX_EPT_IPAT_BIT; >> Signed-off-by: francisco_flynn <francisco_flynn@xxxxxxxxxxx> >> --- >> arch/x86/include/asm/memtype.h | 2 ++ >> arch/x86/kvm/mmu/spte.c | 5 +++-- > > Please use get_maintainers.pl. sure. > >> arch/x86/mm/pat/memtype.c | 8 ++++++++ >> 3 files changed, 13 insertions(+), 2 deletions(-)
