Re: [Xen-devel] [PATCH v13 for-xen-4.5 17/21] x86/VPMU: Handle PMU interrupts for PV guests

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 10/13/2014 11:29 AM, Jan Beulich wrote:
> > > > On 03.10.14 at 23:40, <boris.ostrovsky@xxxxxxxxxx> wrote:
> >   int vpmu_do_wrmsr(unsigned int msr, uint64_t msr_content, uint64_t supported)
> >   {
> > -    struct vpmu_struct *vpmu = vcpu_vpmu(current);
> > +    struct vcpu *curr = current;
> > +    struct vpmu_struct *vpmu = vcpu_vpmu(curr);
> >   
> >       if ( !(vpmu_mode & (XENPMU_MODE_SELF | XENPMU_MODE_HV)) )
> >           return 0;
> >   
> >       if ( vpmu->arch_vpmu_ops && vpmu->arch_vpmu_ops->do_wrmsr )
> > -        return vpmu->arch_vpmu_ops->do_wrmsr(msr, msr_content, supported);
> > +    {
> > +        int ret = vpmu->arch_vpmu_ops->do_wrmsr(msr, msr_content, supported);
> > +
> > +        /*
> > +         * We may have received a PMU interrupt during WRMSR handling
> > +         * and since do_wrmsr may load VPMU context we should save
> > +         * (and unload) it again.
> > +         */
> Is this btw true also when do_wrmsr() failed? Or could you not rather
> handle ret != 0 before the following if() (or check ret == 0 together
> with the other conditions)?
There is indeed no need to save/unload if do_wrmsr() failed but one of 
conditions in the if() that you refer to (PMU_CACHED bit test) can only 
happen if do_wrmsr() succeeded because the context could not have been 
loaded in case of failure.
-boris


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