Re: [PATCH] KVM: x86: fix initial PAT value

[Wanpeng Li]

Hi Radim,
On Mon, Apr 27, 2015 at 03:11:25PM +0200, Radim KrÄmÃÅ wrote:
>PAT should be 0007_0406_0007_0406h on RESET and not modified on INIT.

Could you point out where this value is described in SDM? :)

Regards,
Wanpeng Li 

>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 KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
>---
> 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;
>-- 
>2.3.6
>
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