Messages in this thread | | | Subject | Re: [PATCH v2 2/2] KVM: MMU: consider host cache mode in MMIO page check | From | Xiao Guangrong <> | Date | Thu, 2 Nov 2017 15:56:31 +0800 |
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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 <haozhong.zhang@intel.com> > Reported-by: Cuevas Escareno, Ivan D <ivan.d.cuevas.escareno@intel.com> > Reported-by: Kumar, Karthik <karthik.kumar@intel.com> > --- > 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.
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