linux-kernel - Re: [PATCH] KVM: x86: Fix page-tables reserved bits

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Date:	Wed, 16 Apr 2014 16:03:29 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Nadav Amit <namit@...technion.ac.il>
Cc:	gleb@...nel.org, pbonzini@...hat.com, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: Fix page-tables reserved bits

On Fri, Apr 04, 2014 at 06:31:04AM +0300, Nadav Amit wrote:
> KVM does not handle the reserved bits of x86 page tables correctly:
> In PAE, bits 5:8 are reserved in the PDPTE.
> In IA-32e, bit 8 is not reserved.
> 
> Signed-off-by: Nadav Amit <namit@...technion.ac.il>
> ---
>  arch/x86/kvm/mmu.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index f5704d9..3993976 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -3538,7 +3538,7 @@ static void reset_rsvds_bits_mask(struct kvm_vcpu *vcpu,
>  	case PT32E_ROOT_LEVEL:
>  		context->rsvd_bits_mask[0][2] =
>  			rsvd_bits(maxphyaddr, 63) |
> -			rsvd_bits(7, 8) | rsvd_bits(1, 2);	/* PDPTE */
> +			rsvd_bits(5, 8) | rsvd_bits(1, 2);	/* PDPTE */
>  		context->rsvd_bits_mask[0][1] = exb_bit_rsvd |
>  			rsvd_bits(maxphyaddr, 62);	/* PDE */
>  		context->rsvd_bits_mask[0][0] = exb_bit_rsvd |
> @@ -3550,9 +3550,9 @@ static void reset_rsvds_bits_mask(struct kvm_vcpu *vcpu,
>  		break;
>  	case PT64_ROOT_LEVEL:
>  		context->rsvd_bits_mask[0][3] = exb_bit_rsvd |
> -			rsvd_bits(maxphyaddr, 51) | rsvd_bits(7, 8);
> +			rsvd_bits(maxphyaddr, 51) | rsvd_bits(7, 7);
>  		context->rsvd_bits_mask[0][2] = exb_bit_rsvd |
> -			rsvd_bits(maxphyaddr, 51) | rsvd_bits(7, 8);
> +			rsvd_bits(maxphyaddr, 51) | rsvd_bits(7, 7);

Bit 7 is not reserved either, for the PDPTE (its PageSize bit).

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