On 10/31/2017 07:48 PM, Haozhong Zhang wrote:
> Some reserved pages, such as those from NVDIMM DAX devices, are
> not for MMIO, and can be mapped with cached memory type for better
> performance. However, the above check misconceives those pages as
> MMIO. Because KVM maps MMIO pages with UC memory type, the
> performance of guest accesses to those pages would be harmed.
> Therefore, we check the host memory type by lookup_memtype() in
> addition and only treat UC/UC- pages as MMIO.
>
> Signed-off-by: Haozhong Zhang <[email protected]>
> Reported-by: Cuevas Escareno, Ivan D <[email protected]>
> Reported-by: Kumar, Karthik <[email protected]>
> ---
> arch/x86/kvm/mmu.c | 30 +++++++++++++++++++++++++++---
> 1 file changed, 27 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 0b481cc9c725..206828d18857 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2707,10 +2707,34 @@ static bool mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
>
> static bool kvm_is_mmio_pfn(kvm_pfn_t pfn)
> {
> - if (pfn_valid(pfn))
> - return !is_zero_pfn(pfn) && PageReserved(pfn_to_page(pfn));
> + bool is_mmio = true;
>
> - return true;
> + if (pfn_valid(pfn)) {
> + is_mmio = !is_zero_pfn(pfn) && PageReserved(pfn_to_page(pfn));
> +
> + /*
> + * Some reserved pages, such as those from NVDIMM DAX
> + * devices, are not for MMIO, and can be mapped with
> + * cached memory type for better performance. However,
> + * the above check misconceives those pages as MMIO.
> + * Because KVM maps MMIO pages with UC memory type,
> + * the performance of guest accesses to those pages
> + * would be harmed. Therefore, we check the host
> + * memory type by lookup_memtype() in addition and
> + * only treat UC/UC- pages as MMIO.
> + *
> + * lookup_memtype() works only when PAT is enabled, so
> + * add pat_enabled() check here.
> + */
> + if (is_mmio && pat_enabled()) {
> + enum page_cache_mode cm = lookup_memtype(PFN_PHYS(pfn));
> +
> + is_mmio = (cm == _PAGE_CACHE_MODE_UC ||
> + cm == _PAGE_CACHE_MODE_UC_MINUS);
> + }
> + }
You can move all of these detailed stuffs to pat.c and abstract them by introducing
a function, maybe named pat_pfn_is_uc(). I think this is what Ingo wants.
From 1582773766176775393@xxx Tue Oct 31 11:51:29 +0000 2017
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