linux-kernel - Re: [PATCH v2] KVM MMU: check reserved bits only when CR4.PSE=1 or CR4.PAE=1

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Date:	Wed, 17 Mar 2010 23:49:48 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Avi Kivity <avi@...hat.com>, Sheng Yang <sheng@...ux.intel.com>,
	KVM list <kvm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] KVM MMU: check reserved bits only when CR4.PSE=1 or
 CR4.PAE=1

On Wed, Mar 17, 2010 at 11:43:06AM +0800, Xiao Guangrong wrote:
> - The RSV bit is possibility set in error code when #PF occurred
>   only if CR4.PSE=1 or CR4.PAE=1
>   
> - context->rsvd_bits_mask[1][0] is always 0
> 
> Changlog:
> Move this operation to reset_rsvds_bits_mask() address Avi Kivity's suggestion
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
> ---
>  arch/x86/kvm/mmu.c |   12 +++++++++---
>  1 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index b137515..c49f8ec 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2288,18 +2288,26 @@ static void reset_rsvds_bits_mask(struct kvm_vcpu *vcpu, int level)
>  
>  	if (!is_nx(vcpu))
>  		exb_bit_rsvd = rsvd_bits(63, 63);
> +
> +	context->rsvd_bits_mask[1][0] = 0;

So if the guest enables PAT at PTE level you completly disable reserved
bit checking? You should only disable checking for [1][1] if !PSE.

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