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.
Changes in v5:
* Rename pat_pfn_is_uc() into pat_pfn_is_uc_or_uc_minus() to avoid
confusion.
* Drop converters between kvm_pfn_t and pfn_t, because they are not
necessary. pat_pfn_is_uc_or_uc_minus() does not need flags in
pfn_t, so we can only pass a raw unsigned long to it.
Changes in v4:
* Mask pfn_t and kvm_pfn_t specific flags in conversion.
Changes in v3:
* Move cache mode check to pat.c as pat_pfn_is_uc()
* Reintroduce converters between kvm_pfn_t and pfn_t.
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: add functions to check if a pfn is UC/UC-
KVM: MMU: consider host cache mode in MMIO page check
arch/x86/include/asm/pat.h | 2 ++
arch/x86/kvm/mmu.c | 15 ++++++++++++++-
arch/x86/mm/pat.c | 16 ++++++++++++++++
3 files changed, 32 insertions(+), 1 deletion(-)
--
2.14.1
From 1583468116457181289@xxx Wed Nov 08 03:47:53 +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 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 | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 0b481cc9c725..7715476bc5c9 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2708,7 +2708,20 @@ 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_enabled() || pat_pfn_is_uc_or_uc_minus(pfn));
return true;
}
--
2.14.1
From 1583468622039692839@xxx Wed Nov 08 03:55:55 +0000 2017
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