[I just copy the commit message from patch 2]
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.
Changes in v2:
* Switch to lookup_memtype() to get host memory type.
* Rewrite the comment in KVM MMU patch.
* Remove v1 patch 2, which is not necessary in v2.
Haozhong Zhang (2):
x86/mm: expose lookup_memtype()
KVM: MMU: consider host cache mode in MMIO page check
arch/x86/include/asm/pat.h | 2 ++
arch/x86/kvm/mmu.c | 30 +++++++++++++++++++++++++++---
arch/x86/mm/pat.c | 3 ++-
3 files changed, 31 insertions(+), 4 deletions(-)
--
2.14.1
From 1583622119520057457@xxx Thu Nov 09 20:35:42 +0000 2017
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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);
+ }
+ }
+
+ return is_mmio;
}
static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
--
2.14.1
From 1582940863145819526@xxx Thu Nov 02 08:07:25 +0000 2017
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