| Message ID | 20171108075630.16991-3-haozhong.zhang@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 08/11/2017 08:56, Haozhong Zhang wrote: > 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 <haozhong.zhang@intel.com> > Reported-by: Cuevas Escareno, Ivan D <ivan.d.cuevas.escareno@intel.com> > Reported-by: Kumar, Karthik <karthik.kumar@intel.com> WC should be allowed as well, because the combination of EPT_PAT=UC and gPAT=WC gives WC effective memory type. Maybe it's better after all if the lookup_memtype call remains in kvm_is_mmio_pfn, like if (!pfn_valid(pfn)) return true; if (is_zero_pfn(pfn) || !PageReserved(pfn_to_page(pfn)) return false; /* ... long comment ... */ if (!pat_enabled() return true; else { cm = lookup_memtype(PFN_PHYS(pfn)); return cm == ... } or something like that. Thanks, Paolo > --- > 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; > } >
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; }
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 <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 | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)