@@ -2708,7 +2708,23 @@ 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_to_pfn(pfn)));
return true;
}
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 | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-)