linux-kernel - [PATCH 1/9] KVM: MMU: fix decoding cache type from MTRR

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Date:	Thu, 30 Apr 2015 18:24:42 +0800
From:	guangrong.xiao@...ux.intel.com
To:	pbonzini@...hat.com
Cc:	gleb@...nel.org, mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
Subject: [PATCH 1/9] KVM: MMU: fix decoding cache type from MTRR

From: Xiao Guangrong <guangrong.xiao@...ux.intel.com>

There are some bugs in current get_mtrr_type();
1: bit 2 of mtrr_state->enabled is corresponding bit 11 of IA32_MTRR_DEF_TYPE
   MSR which completely control MTRR's enablement that means other bits are
   ignored if it is cleared

2: the fixed MTRR ranges are controlled by bit 1 of mtrr_state->enabled (bit 10
   of IA32_MTRR_DEF_TYPE)

3: if MTRR is disabled, UC is applied to all of physical memory rather than
   mtrr_state->def_type

Signed-off-by: Xiao Guangrong <guangrong.xiao@...ux.intel.com>
---
 arch/x86/kvm/mmu.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index d43867c..ea3e3e4 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2393,19 +2393,20 @@ EXPORT_SYMBOL_GPL(kvm_mmu_unprotect_page);
 static int get_mtrr_type(struct mtrr_state_type *mtrr_state,
 			 u64 start, u64 end)
 {
-	int i;
 	u64 base, mask;
 	u8 prev_match, curr_match;
-	int num_var_ranges = KVM_NR_VAR_MTRR;
+	int i, num_var_ranges = KVM_NR_VAR_MTRR;
 
-	if (!mtrr_state->enabled)
-		return 0xFF;
+	/* MTRR is completely disabled, use UC for all of physical memory. */
+	if (!(mtrr_state->enabled & 0x2))
+		return MTRR_TYPE_UNCACHABLE;
 
 	/* Make end inclusive end, instead of exclusive */
 	end--;
 
 	/* Look in fixed ranges. Just return the type as per start */
-	if (mtrr_state->have_fixed && (start < 0x100000)) {
+	if (mtrr_state->have_fixed && (mtrr_state->enabled & 0x1) &&
+	      (start < 0x100000)) {
 		int idx;
 
 		if (start < 0x80000) {
@@ -2428,9 +2429,6 @@ static int get_mtrr_type(struct mtrr_state_type *mtrr_state,
 	 * Look of multiple ranges matching this address and pick type
 	 * as per MTRR precedence
 	 */
-	if (!(mtrr_state->enabled & 2))
-		return mtrr_state->def_type;
-
 	prev_match = 0xFF;
 	for (i = 0; i < num_var_ranges; ++i) {
 		unsigned short start_state, end_state;
-- 
1.9.3

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