KVM: MTRR: treat memory as writeback if MTRR is disabled in guest CPUID

[firefly-linux-kernel-4.4.55.git] / arch / x86 / kvm / mtrr.c

diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
index 7747b6d716fa75aeb8a64448b44c15d73d91a88f..3f8c732117eccf73140fded817e1b155dfa76073 100644 (file)
--- a/arch/x86/kvm/mtrr.c
+++ b/arch/x86/kvm/mtrr.c
@@ -120,14 +120,22 @@ static u8 mtrr_default_type(struct kvm_mtrr *mtrr_state)
        return mtrr_state->deftype & IA32_MTRR_DEF_TYPE_TYPE_MASK;
 }
 
-static u8 mtrr_disabled_type(void)
+static u8 mtrr_disabled_type(struct kvm_vcpu *vcpu)
 {
        /*
         * Intel SDM 11.11.2.2: all MTRRs are disabled when
         * IA32_MTRR_DEF_TYPE.E bit is cleared, and the UC
         * memory type is applied to all of physical memory.
+        *
+        * However, virtual machines can be run with CPUID such that
+        * there are no MTRRs.  In that case, the firmware will never
+        * enable MTRRs and it is obviously undesirable to run the
+        * guest entirely with UC memory and we use WB.
         */
-       return MTRR_TYPE_UNCACHABLE;
+       if (guest_cpuid_has_mtrr(vcpu))
+               return MTRR_TYPE_UNCACHABLE;
+       else
+               return MTRR_TYPE_WRBACK;
 }
 
 /*
@@ -675,7 +683,7 @@ u8 kvm_mtrr_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn)
        }
 
        if (iter.mtrr_disabled)
-               return mtrr_disabled_type();
+               return mtrr_disabled_type(vcpu);
 
        /* not contained in any MTRRs. */
        if (type == -1)