linux-kernel - Re: [PATCH] KVM: x86: fix initial PAT value

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Message-ID: <553E3BA9.8000403@redhat.com>
Date:	Mon, 27 Apr 2015 15:37:45 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>,
	linux-kernel@...r.kernel.org
CC:	kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: fix initial PAT value



On 27/04/2015 15:11, Radim Krčmář wrote:
> PAT should be 0007_0406_0007_0406h on RESET and not modified on INIT.
> VMX used a wrong value (host's PAT) and while SVM used the right one,
> it never got to arch.pat.
> 
> This is not an issue with QEMU as it will force the correct value.
> 
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> ---
>  arch/x86/kvm/svm.c |  2 +-
>  arch/x86/kvm/vmx.c | 12 ++----------
>  arch/x86/kvm/x86.c |  2 ++
>  arch/x86/kvm/x86.h |  2 ++
>  4 files changed, 7 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index ce741b8650f6..9aceb4a8c147 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1176,7 +1176,7 @@ static void init_vmcb(struct vcpu_svm *svm)
>  		clr_exception_intercept(svm, PF_VECTOR);
>  		clr_cr_intercept(svm, INTERCEPT_CR3_READ);
>  		clr_cr_intercept(svm, INTERCEPT_CR3_WRITE);
> -		save->g_pat = 0x0007040600070406ULL;
> +		save->g_pat = svm->vcpu.arch.pat;
>  		save->cr3 = 0;
>  		save->cr4 = 0;
>  	}
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index f7b61687bd79..62459382d305 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -4667,16 +4667,8 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
>  	vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, 0);
>  	vmcs_write64(VM_ENTRY_MSR_LOAD_ADDR, __pa(vmx->msr_autoload.guest));
>  
> -	if (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PAT) {
> -		u32 msr_low, msr_high;
> -		u64 host_pat;
> -		rdmsr(MSR_IA32_CR_PAT, msr_low, msr_high);
> -		host_pat = msr_low | ((u64) msr_high << 32);
> -		/* Write the default value follow host pat */
> -		vmcs_write64(GUEST_IA32_PAT, host_pat);
> -		/* Keep arch.pat sync with GUEST_IA32_PAT */
> -		vmx->vcpu.arch.pat = host_pat;
> -	}
> +	if (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PAT)
> +		vmcs_write64(GUEST_IA32_PAT, vmx->vcpu.arch.pat);
>  
>  	for (i = 0; i < ARRAY_SIZE(vmx_msr_index); ++i) {
>  		u32 index = vmx_msr_index[i];
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c73efcd03e29..a20898f9e43a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7363,6 +7363,8 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
>  
>  	vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
>  
> +	vcpu->arch.pat = MSR_IA32_CR_PAT_DEFAULT;
> +
>  	kvm_async_pf_hash_reset(vcpu);
>  	kvm_pmu_init(vcpu);
>  
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index f5fef1868096..01a1d011e073 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -4,6 +4,8 @@
>  #include <linux/kvm_host.h>
>  #include "kvm_cache_regs.h"
>  
> +#define MSR_IA32_CR_PAT_DEFAULT  0x0007040600070406ULL
> +
>  static inline void kvm_clear_exception_queue(struct kvm_vcpu *vcpu)
>  {
>  	vcpu->arch.exception.pending = false;
> 

Applied, thanks.

Paolo
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