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.
Changes in v6: * Rename the function in patch 1 to pat_immune_to_uc_mtrr(). * Consider WC memory type in patch 1. 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 a function to check if a pfn is UC/UC-/WC KVM: MMU: consider host cache mode in MMIO page check arch/x86/include/asm/pat.h | 2 ++ arch/x86/kvm/mmu.c | 13 ++++++++++++- arch/x86/mm/pat.c | 19 +++++++++++++++++++ 3 files changed, 33 insertions(+), 1 deletion(-) -- 2.14.1