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

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Date:	Wed, 6 May 2015 14:42:39 -0700
From:	David Matlack <dmatlack@...gle.com>
To:	guangrong.xiao@...ux.intel.com
Cc:	Paolo Bonzini <pbonzini@...hat.com>,
	Gleb Natapov <gleb@...nel.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	kvm list <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/9] KVM: MMU: fix decoding cache type from MTRR

On Thu, Apr 30, 2015 at 3:24 AM,  <guangrong.xiao@...ux.intel.com> wrote:
> 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

bit 1, not bit 2. (code is correct though)

>    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

bit 0, not bit 1. (code is correct though)

>    of IA32_MTRR_DEF_TYPE)
>
> 3: if MTRR is disabled, UC is applied to all of physical memory rather than
>    mtrr_state->def_type

kvm_get_guest_memory_type defaults to MTRR_TYPE_WRBACK, not
mtrr_state->def_type, when get_mtrr_type returns 0xFF.

>
> 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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