KVM: MMU: consider host cache mode in MMIO page check (aa2e063a) · Commits · 戴 / test

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-/WC 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> Reviewed-by:

Xiao Guangrong <xiaoguangrong@tencent.com> Signed-off-by:

Paolo Bonzini <pbonzini@redhat.com> Signed-off-by:

Radim Krčmář <rkrcmar@redhat.com>

arch/x86/kvm/mmu.c

+13 −1

Original line number	Diff line number	Diff line
		@@ -42,6 +42,7 @@
		#include <linux/kern_levels.h>

		#include <asm/page.h>
		#include <asm/pat.h>
		#include <asm/cmpxchg.h>
		#include <asm/io.h>
		#include <asm/vmx.h>
		@@ -2708,7 +2709,18 @@ 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, and results in KVM mapping them with UC
		* memory type, which would hurt the performance.
		* Therefore, we check the host memory type in addition
		* and only treat UC/UC-/WC pages as MMIO.
		*/
		(!pat_enabled() \|\| pat_pfn_immune_to_uc_mtrr(pfn));

		return true;
		}

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