On Tue, 31 Oct 2017, Haozhong Zhang wrote: > [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 Note that cached memory type on persistent memory has horrible performance. The clwb instruction on Broadwell is very slow - when you write to persistent memory and use clwb to flush cache, the performance is about 350MB/s. Using write-combining memory type for persistent memory is much faster, it can sustain performance of one 8-byte write per tick. Mikulas > 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 >
