Re: [Xen-devel] [PATCH v10 6/7] vmx: VT-d posted-interrupt core logic handling

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> > +    spin_lock_irqsave(&per_cpu(pi_blocked_vcpu_lock, pi_block_cpu),
> flags);
> > +
> > +    /*
> > +     * v->arch.hvm_vmx.pi_block_cpu == NR_CPUS here means the vCPU
> was
> > +     * removed from the blocking list while we are acquiring the lock.
> > +     */
> > +    if ( v->arch.hvm_vmx.pi_block_cpu == NR_CPUS )
> 
> With you wanting to deal with changes behind your back here,
> isn't there come kind of barrier needed between reading and using
> pi_block_cpu, such that the compiler won't convert the local
> variable accesses into multiple reads of
> v->arch.hvm_vmx.pi_block_cpu (which iiuc it is allowed to do)?
> 

Thinking about this more. Seems we call spin_lock_irqsave() before
using  ' v->arch.hvm_vmx.pi_block_cpu ', can spin_lock_irqsave()
used as the serializing instruction here? IIRIC, spin lock operations
can be used for this purpose, right?

Thanks,
Feng

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