On 11/03/2017 01:53 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 | 19 ++++++++++++++++++-
> 1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 0b481cc9c725..e9ed0e666a83 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2708,7 +2708,24 @@ 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));
> + return !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 in addition and
> + * only treat UC/UC- pages as MMIO.
> + *
> + * pat_pfn_is_uc() works only when PAT is enabled,
> + * so check pat_enabled() as well.
> + */
> + (!pat_enabled() ||
> + pat_pfn_is_uc(kvm_pfn_t_to_pfn_t(pfn)));
Can it be compiled if !CONFIG_PAT?
It would be better if we move pat_enabled out of kvm as well, please refer
to pgprot_writecombine() which is implemented in pat.c and in
include\asm-generic\pgtable.h:
#ifndef pgprot_writecombine
#define pgprot_writecombine pgprot_noncached
#endif
From 1583023140618997395@xxx Fri Nov 03 05:55:11 +0000 2017
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