[PATCH 1/3] KVM: MTRR: fix memory type handling if MTRR is completely disabled

[Xiao Guangrong]

From: Xiao Guangrong <guangrong.x...@intel.com>

Currently code uses default memory type if MTRR is fully disabled,
fix it by using UC instead

Signed-off-by: Xiao Guangrong <guangrong.x...@intel.com>
---
 arch/x86/kvm/mtrr.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
index de1d2d8..e275013 100644
--- a/arch/x86/kvm/mtrr.c
+++ b/arch/x86/kvm/mtrr.c
@@ -120,6 +120,16 @@ 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)
+{
+       /*
+        * 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.
+        */
+       return MTRR_TYPE_UNCACHABLE;
+}
+
 /*
 * Three terms are used in the following code:
 * - segment, it indicates the address segments covered by fixed MTRRs.
@@ -434,6 +444,8 @@ struct mtrr_iter {
 
        /* output fields. */
        int mem_type;
+       /* mtrr is completely disabled? */
+       bool mtrr_disabled;
        /* [start, end) is not fully covered in MTRRs? */
        bool partial_map;
 
@@ -549,7 +561,7 @@ static void mtrr_lookup_var_next(struct mtrr_iter *iter)
 static void mtrr_lookup_start(struct mtrr_iter *iter)
 {
        if (!mtrr_is_enabled(iter->mtrr_state)) {
-               iter->partial_map = true;
+               iter->mtrr_disabled = true;
                return;
        }
 
@@ -563,6 +575,7 @@ static void mtrr_lookup_init(struct mtrr_iter *iter,
        iter->mtrr_state = mtrr_state;
        iter->start = start;
        iter->end = end;
+       iter->mtrr_disabled = false;
        iter->partial_map = false;
        iter->fixed = false;
        iter->range = NULL;
@@ -656,6 +669,9 @@ u8 kvm_mtrr_get_guest_memory_type(struct kvm_vcpu *vcpu, 
gfn_t gfn)
                return MTRR_TYPE_WRBACK;
        }
 
+       if (iter.mtrr_disabled)
+               return mtrr_disabled_type();
+
        /* It is not covered by MTRRs. */
        if (iter.partial_map) {
                /*
@@ -689,6 +705,9 @@ bool kvm_mtrr_check_gfn_range_consistency(struct kvm_vcpu 
*vcpu, gfn_t gfn,
                        return false;
        }
 
+       if (iter.mtrr_disabled)
+               return true;
+
        if (!iter.partial_map)
                return true;
 
-- 
2.1.0

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