linux-kernel - Re: [PATCH v3 01/10] KVM: MMU: fix decoding cache type from MTRR

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Date:	Wed, 13 May 2015 16:09:21 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
Cc:	pbonzini@...hat.com, gleb@...nel.org, mtosatti@...hat.com,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 01/10] KVM: MMU: fix decoding cache type from MTRR

On Wed, May 13, 2015 at 02:42:19PM +0800, Xiao Guangrong wrote:
>There are some bugs in current get_mtrr_type();
>1: bit 1 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 0 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>

Reviewed-by: Wanpeng Li <wanpeng.li@...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 b78e83f..d00cebd 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;
>-- 
>2.1.0
>
>--
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