linux-kernel - Re: [PATCH v2 3/3] KVM: x86: #GP when attempts to write reserved bits of Variable Range MTRRs

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Date:	Tue, 19 Aug 2014 11:11:00 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Wanpeng Li <wanpeng.li@...ux.intel.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	Gleb Natapov <gleb@...nel.org>,
	Zhang Yang <yang.z.zhang@...el.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] KVM: x86: #GP when attempts to write reserved
 bits of Variable Range MTRRs

Il 19/08/2014 11:04, Wanpeng Li ha scritto:
> Section 11.11.2.3 of the SDM mentions "All other bits in the IA32_MTRR_PHYSBASEn 
> and IA32_MTRR_PHYSMASKn registers are reserved; the processor generates a 
> general-protection exception(#GP) if software attempts to write to them". This 
> patch do it in kvm.
> 
> Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>
> ---
>  arch/x86/kvm/x86.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index fb3ea7a..b85da5f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1726,6 +1726,7 @@ static bool valid_mtrr_type(unsigned t)
>  static bool mtrr_valid(struct kvm_vcpu *vcpu, u32 msr, u64 data)
>  {
>  	int i;
> +	u64 mask = 0;
>  
>  	if (!msr_mtrr_valid(msr))
>  		return false;
> @@ -1749,10 +1750,21 @@ static bool mtrr_valid(struct kvm_vcpu *vcpu, u32 msr, u64 data)
>  	/* variable MTRRs */
>  	WARN_ON(!(msr >= 0x200 && msr < 0x200 + 2 * KVM_NR_VAR_MTRR));
>  
> -	if ((msr & 1) == 0)
> +	for (i = 63; i > boot_cpu_data.x86_phys_bits; i--)
> +		mask |= (1ULL << i);
> +	if ((msr & 1) == 0) {
>  		/* MTRR base */
> -		return valid_mtrr_type(data & 0xff);
> -	/* MTRR mask */
> +		if (!valid_mtrr_type(data & 0xff))
> +			return false;
> +		 mask |= 0xf00;
> +	} else
> +		/* MTRR mask */
> +		mask |= 0x7ff;
> +	if (data & mask) {
> +		kvm_inject_gp(vcpu, 0);
> +		return false;
> +	}
> +
>  	return true;
>  }
>  
> 

Thanks, these two patches look good.  Please write a testcase for
kvm-unit-tests (x86/msr.c), too.

Paolo
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