Xen devel - Apr 2011 - [PATCH][RFC] FPU LWP 4/5: enable LWP for SVM guest

This patch enables LWP support for SVM guests. It saves and restores 
LWP_CFG MSRs on each VCPU context switch. Additionally it handles LWP 
CPUIDs and MSRs.

Signed-off-by: Wei Huang <wei.huang2@amd.com>



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>>> On 14.04.11 at 22:39, Wei Huang <wei.huang2@amd.com> 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.

Jan


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