0003-mttr.patch

   1 From e24dea2afc6a0852983dc741072d8e96155e13f5 Mon Sep 17 00:00:00 2001
   2 From: Paolo Bonzini <pbonzini@redhat.com>
   3 Date: Tue, 22 Dec 2015 15:20:00 +0100
   4 Subject: KVM: MTRR: treat memory as writeback if MTRR is disabled in guest
   5  CPUID
   6
   7 Virtual machines can be run with CPUID such that there are no MTRRs.
   8 In that case, the firmware will never enable MTRRs and it is obviously
   9 undesirable to run the guest entirely with UC memory.  Check out guest
  10 CPUID, and use WB memory if MTRR do not exist.
  11
  12 Cc: qemu-stable@nongnu.org
  13 Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=107561
  14 Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
  15 ---
  16  arch/x86/kvm/cpuid.h |  8 ++++++++
  17  arch/x86/kvm/mtrr.c  | 14 +++++++++++---
  18  2 files changed, 19 insertions(+), 3 deletions(-)
  19
  20 diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
  21 index 06332cb..3f5c48d 100644
  22 --- a/arch/x86/kvm/cpuid.h
  23 +++ b/arch/x86/kvm/cpuid.h
  24 @@ -38,6 +38,14 @@ static inline bool guest_cpuid_has_xsave(struct kvm_vcpu *vcpu)
  25         return best && (best->ecx & bit(X86_FEATURE_XSAVE));
  26  }
  27
  28 +static inline bool guest_cpuid_has_mtrr(struct kvm_vcpu *vcpu)
  29 +{
  30 +       struct kvm_cpuid_entry2 *best;
  31 +
  32 +       best = kvm_find_cpuid_entry(vcpu, 1, 0);
  33 +       return best && (best->edx & bit(X86_FEATURE_MTRR));
  34 +}
  35 +
  36  static inline bool guest_cpuid_has_tsc_adjust(struct kvm_vcpu *vcpu)
  37  {
  38         struct kvm_cpuid_entry2 *best;
  39 diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
  40 index 7747b6d..3f8c732 100644
  41 --- a/arch/x86/kvm/mtrr.c
  42 +++ b/arch/x86/kvm/mtrr.c
  43 @@ -120,14 +120,22 @@ static u8 mtrr_default_type(struct kvm_mtrr *mtrr_state)
  44         return mtrr_state->deftype & IA32_MTRR_DEF_TYPE_TYPE_MASK;
  45  }
  46
  47 -static u8 mtrr_disabled_type(void)
  48 +static u8 mtrr_disabled_type(struct kvm_vcpu *vcpu)
  49  {
  50         /*
  51          * Intel SDM 11.11.2.2: all MTRRs are disabled when
  52          * IA32_MTRR_DEF_TYPE.E bit is cleared, and the UC
  53          * memory type is applied to all of physical memory.
  54 +        *
  55 +        * However, virtual machines can be run with CPUID such that
  56 +        * there are no MTRRs.  In that case, the firmware will never
  57 +        * enable MTRRs and it is obviously undesirable to run the
  58 +        * guest entirely with UC memory and we use WB.
  59          */
  60 -       return MTRR_TYPE_UNCACHABLE;
  61 +       if (guest_cpuid_has_mtrr(vcpu))
  62 +               return MTRR_TYPE_UNCACHABLE;
  63 +       else
  64 +               return MTRR_TYPE_WRBACK;
  65  }
  66
  67  /*
  68 @@ -675,7 +683,7 @@ u8 kvm_mtrr_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn)
  69         }
  70
  71         if (iter.mtrr_disabled)
  72 -               return mtrr_disabled_type();
  73 +               return mtrr_disabled_type(vcpu);
  74
  75         /* not contained in any MTRRs. */
  76         if (type == -1)
  77 --
  78 cgit v0.11.2