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Re: [Xen-devel] [PATCH][RFC] FPU LWP 4/5: enable LWP for SVM guest

To: "Wei Huang" <wei.huang2@xxxxxxx>
Subject: Re: [Xen-devel] [PATCH][RFC] FPU LWP 4/5: enable LWP for SVM guest
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Fri, 15 Apr 2011 10:17:30 +0100
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>>> On 14.04.11 at 22:39, Wei Huang <wei.huang2@xxxxxxx> wrote:
>+static void svm_lwp_save(struct vcpu *v)
>+    if ( cpu_has_lwp )
>+    {
>+        rdmsrl(MSR_AMD64_LWP_CFG, v->arch.hvm_svm.guest_lwp_cfg);
>+        wrmsrl(MSR_AMD64_LWP_CFG, 0x0);
>+        /* Disable LWP for next VCPU */
>+        wrmsrl(MSR_AMD64_LWP_CBADDR, 0x0);
>+    }
>+static void svm_lwp_load(struct vcpu *v)
>+    if ( cpu_has_lwp ) 
>+    {
>+        /* Only LWP_CFG is reloaded. LWP_CBADDR will be reloaded via xrstor */
>+        wrmsrl(MSR_AMD64_LWP_CFG, v->arch.hvm_svm.guest_lwp_cfg);
>+    }

I think I had pointed this out before - to avoid these MSR accesses
for guests not using LWP, you should track whether the vCPU has
LWP support enabled (e.g. non-zero written into LWP_CFG) and
key off of that instead of cpu_has_lwp.


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