Re: [Xen-devel] [PATCH v2 11/13] x86/PMU: Handle PMU interrupts for PV guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.09.13 at 11:42, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote:
> Add support for handling PMU interrupts for PV guests, make these interrupts
> NMI instead of PMU_APIC_VECTOR vector. Depending on vpmu_mode forward the
> interrupts to appropriate guest (mode is VPMU_ON) or to dom0 (VPMU_DOM0).

Is using NMIs here a necessity? I guess not, in which case I'd really
like this to be a (perhaps even non-default) option controllable via
command line option.

> - * This interrupt handles performance counters interrupt
> - */
> -
> -void pmu_apic_interrupt(struct cpu_user_regs *regs)
> -{
> -    ack_APIC_irq();
> -    vpmu_do_interrupt(regs);
> -}

So this was the only caller of vpmu_do_interrupt(); no new one gets
added in this patch afaics, and I don't recall having seen addition of
another caller in earlier patches. What's the deal?

> @@ -99,17 +106,97 @@ int vpmu_do_rdmsr(unsigned int msr, uint64_t 
> *msr_content)
>  int vpmu_do_interrupt(struct cpu_user_regs *regs)
>  {
>      struct vcpu *v = current;
> -    struct vpmu_struct *vpmu = vcpu_vpmu(v);
> +    struct vpmu_struct *vpmu;
>  
> -    if ( vpmu->arch_vpmu_ops )
> +
> +    /* dom0 will handle this interrupt */
> +    if ( (vpmu_mode & XENPMU_MODE_PRIV) ||
> +        (v->domain->domain_id >= DOMID_FIRST_RESERVED) )
> +    {
> +            if ( smp_processor_id() >= dom0->max_vcpus )
> +                return 0;
> +            v = dom0->vcpu[smp_processor_id()];
> +    }
> +
> +    vpmu = vcpu_vpmu(v);
> +    if ( !vpmu_is_set(vpmu, VPMU_CONTEXT_ALLOCATED) )
> +        return 0;
> +
> +    if ( !is_hvm_domain(v->domain) || (vpmu_mode & XENPMU_MODE_PRIV) )
> +    {
> +        /* PV guest or dom0 is doing system profiling */
> +        void *p;
> +        struct cpu_user_regs *gregs;
> +
> +        p = &v->arch.vpmu.xenpmu_data->pmu.regs;
> +
> +        /* PV guest will be reading PMU MSRs from xenpmu_data */
> +        vpmu_save_force(v);
> +
> +        /* Store appropriate registers in xenpmu_data
> +         *
> +         * Note: '!current->is_running' is possible when 'set_current(next)'
> +         * for the (HVM) guest has been called but 'reset_stack_and_jump()'
> +         * has not (i.e. the guest is not actually running yet).
> +         */
> +        if ( !is_hvm_domain(current->domain) ||
> +             ((vpmu_mode & XENPMU_MODE_PRIV) && !current->is_running) )
> +        {
> +            /*
> +             * 32-bit dom0 cannot process Xen's addresses (which are 64 bit)
> +             * and therefore we treat it the same way as a non-priviledged
> +             * PV 32-bit domain.
> +             */
> +            if ( is_pv_32bit_domain(current->domain) )
> +            {
> +                struct compat_cpu_user_regs cmp;
> +
> +                gregs = guest_cpu_user_regs();
> +                XLAT_cpu_user_regs(&cmp, gregs);
> +                memcpy(p, &cmp, sizeof(struct compat_cpu_user_regs));
> +            }
> +            else if ( (current->domain != dom0) && !is_idle_vcpu(current) &&
> +                !(vpmu_mode & XENPMU_MODE_PRIV) )
> +            {
> +                /* PV guest */
> +                gregs = guest_cpu_user_regs();
> +                memcpy(p, gregs, sizeof(struct cpu_user_regs));
> +            }
> +            else
> +                memcpy(p, regs, sizeof(struct cpu_user_regs));
> +        }
> +        else
> +        {
> +            /* HVM guest */
> +            struct segment_register cs;
> +
> +            gregs = guest_cpu_user_regs();
> +            hvm_get_segment_register(current, x86_seg_cs, &cs);
> +            gregs->cs = cs.attr.fields.dpl;
> +
> +            memcpy(p, gregs, sizeof(struct cpu_user_regs));
> +        }
> +
> +        v->arch.vpmu.xenpmu_data->domain_id = current->domain->domain_id;
> +        v->arch.vpmu.xenpmu_data->vcpu_id = current->vcpu_id;
> +        v->arch.vpmu.xenpmu_data->pcpu_id = smp_processor_id();
> +
> +        raise_softirq(PMU_SOFTIRQ);
> +        vpmu_set(vpmu, VPMU_WAIT_FOR_FLUSH);
> +
> +        return 1;
> +    }
> +    else  if ( vpmu->arch_vpmu_ops )
>      {
> -        struct vlapic *vlapic = vcpu_vlapic(v);
> +        /* HVM guest */
> +        struct vlapic *vlapic;
>          u32 vlapic_lvtpc;
>          unsigned char int_vec;
>  
>          if ( !vpmu->arch_vpmu_ops->do_interrupt(regs) )
>              return 0;
>  
> +        vlapic = vcpu_vlapic(v);
>          if ( !is_vlapic_lvtpc_enabled(vlapic) )
>              return 1;
>  

Assuming the plan is to run this in NMI context - this is _a lot_ of
stuff you want to do. Did you carefully audit all paths for being
NMI-safe?

Jan

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