Re: [Xen-devel] [PATCH] Always save/restore performance counters when HVM guest switching VCPU

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 03/01/2013 03:49 PM, suravee.suthikulpanit@xxxxxxx wrote:
> From: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
>
> Currently, the performance counter registers are saved/restores
> when the HVM guest switchs VCPUs only if they are running.
> However, PERF has one check where it writes the MSR and read back
> the value to check if the MSR is working.  This has shown to fails
> the check if the VCPU is moved in between rdmsr and wrmsr and
> resulting in the values are different.
>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
Description may need to be cleaned up a bit but other than that

Acked-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

> ---
>   xen/arch/x86/hvm/svm/vpmu.c |   62 ++++++++++++++++++++++++-------------------
>   1 file changed, 35 insertions(+), 27 deletions(-)
>
> diff --git a/xen/arch/x86/hvm/svm/vpmu.c b/xen/arch/x86/hvm/svm/vpmu.c
> index bf186fe..4854cf3 100644
> --- a/xen/arch/x86/hvm/svm/vpmu.c
> +++ b/xen/arch/x86/hvm/svm/vpmu.c
> @@ -172,12 +172,16 @@ static inline void context_restore(struct vcpu *v)
>       {
>           wrmsrl(counters[i], ctxt->counters[i]);
>   
> +        if ( !vpmu_is_set(vpmu, VPMU_RUNNING) )
> +            continue;
> +
>           /* Force an interrupt to allow guest reset the counter,
>           if the value is positive */
>           if ( is_overflowed(ctxt->counters[i]) && (ctxt->counters[i] > 0) )
>           {
>               gdprintk(XENLOG_WARNING, "VPMU: Force a performance counter "
> -                "overflow interrupt!\n");
> +                "overflow interrupt! (counter:%u value:0x%lx)\n",
> +                i, ctxt->counters[i]);
>               amd_vpmu_do_interrupt(0);
>           }
>       }
> @@ -188,12 +192,13 @@ static void amd_vpmu_restore(struct vcpu *v)
>       struct vpmu_struct *vpmu = vcpu_vpmu(v);
>       struct amd_vpmu_context *ctxt = vpmu->context;
>   
> -    if ( !(vpmu_is_set(vpmu, VPMU_CONTEXT_ALLOCATED) &&
> -           vpmu_is_set(vpmu, VPMU_RUNNING)) )
> +    if ( !(vpmu_is_set(vpmu, VPMU_CONTEXT_ALLOCATED)) )
>           return;
>   
>       context_restore(v);
> -    apic_write(APIC_LVTPC, ctxt->hw_lapic_lvtpc);
> +
> +    if ( vpmu_is_set(vpmu, VPMU_RUNNING) )
> +        apic_write(APIC_LVTPC, ctxt->hw_lapic_lvtpc);
>   }
>   
>   static inline void context_save(struct vcpu *v)
> @@ -214,13 +219,16 @@ static void amd_vpmu_save(struct vcpu *v)
>       struct vpmu_struct *vpmu = vcpu_vpmu(v);
>       struct amd_vpmu_context *ctx = vpmu->context;
>   
> -    if ( !(vpmu_is_set(vpmu, VPMU_CONTEXT_ALLOCATED) &&
> -           vpmu_is_set(vpmu, VPMU_RUNNING)) )
> +    if ( !(vpmu_is_set(vpmu, VPMU_CONTEXT_ALLOCATED)) )
>           return;
>   
>       context_save(v);
> -    ctx->hw_lapic_lvtpc = apic_read(APIC_LVTPC);
> -    apic_write(APIC_LVTPC,  ctx->hw_lapic_lvtpc | APIC_LVT_MASKED);
> +
> +    if ( vpmu_is_set(vpmu, VPMU_RUNNING) )
> +    {
> +        ctx->hw_lapic_lvtpc = apic_read(APIC_LVTPC);
> +        apic_write(APIC_LVTPC,  ctx->hw_lapic_lvtpc | APIC_LVT_MASKED);
> +    }
>   }
>   
>   static void context_update(unsigned int msr, u64 msr_content)
> @@ -303,25 +311,25 @@ static int amd_vpmu_initialise(struct vcpu *v)
>   
>       if ( counters == NULL )
>       {
> -         switch ( family )
> -        {
> -        case 0x15:
> -            num_counters = F15H_NUM_COUNTERS;
> -            counters = AMD_F15H_COUNTERS;
> -            ctrls = AMD_F15H_CTRLS;
> -            k7_counters_mirrored = 1;
> -            break;
> -        case 0x10:
> -        case 0x12:
> -        case 0x14:
> -        case 0x16:
> -        default:
> -            num_counters = F10H_NUM_COUNTERS;
> -            counters = AMD_F10H_COUNTERS;
> -            ctrls = AMD_F10H_CTRLS;
> -            k7_counters_mirrored = 0;
> -            break;
> -        }
> +        switch ( family )
> +        {
> +        case 0x15:
> +            num_counters = F15H_NUM_COUNTERS;
> +            counters = AMD_F15H_COUNTERS;
> +            ctrls = AMD_F15H_CTRLS;
> +            k7_counters_mirrored = 1;
> +            break;
> +        case 0x10:
> +        case 0x12:
> +        case 0x14:
> +        case 0x16:
> +        default:
> +            num_counters = F10H_NUM_COUNTERS;
> +            counters = AMD_F10H_COUNTERS;
> +            ctrls = AMD_F10H_CTRLS;
> +            k7_counters_mirrored = 0;
> +            break;
> +        }
>       }
>   
>       ctxt = xzalloc(struct amd_vpmu_context);

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