Re: [Xen-devel] [PATCH v2 3/4] VMX: Assign the right value to 'NDST' field in a concern case

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

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Tuesday, May 31, 2016 7:58 PM
> To: Wu, Feng <feng.wu@xxxxxxxxx>
> Cc: andrew.cooper3@xxxxxxxxxx; dario.faggioli@xxxxxxxxxx;
> george.dunlap@xxxxxxxxxxxxx; Tian, Kevin <kevin.tian@xxxxxxxxx>; xen-
> devel@xxxxxxxxxxxxx; konrad.wilk@xxxxxxxxxx; keir@xxxxxxx
> Subject: RE: [PATCH v2 3/4] VMX: Assign the right value to 'NDST' field in a
> concern case
> 
> >>> On 31.05.16 at 12:27, <feng.wu@xxxxxxxxx> wrote:
> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> Sent: Friday, May 27, 2016 10:00 PM
> >> >>> On 26.05.16 at 15:39, <feng.wu@xxxxxxxxx> wrote:
> >> > Normally, in vmx_cpu_block() 'NDST' filed should have the same
> >> > value with 'dest' or 'MASK_INSR(dest, PI_xAPIC_NDST_MASK)' depending
> >> > on whether x2apic is enabled. However, in the following scenario,
> >> > 'NDST' has different value:
> >> >
> >> > 'vcpu_block' hook gets assigned in vmx_pi_hooks_assign(), but all
> >> > other three PI hooks have not been assigned or not been excuted yet.
> >> > And during this interval, we are running in vmx_vcpu_block(), then
> >> > 'NDST' may have different value.
> >>
> >> How about simply assigning vcpu_block last? Or alternatively
> >> holding pi_blocking_list_lock around all four assignments? Or
> >> (maybe in addition to one of these) writing something sensible in
> >> vmx_pi_hooks_assign() before doing the hook assignments?
> >
> > The problem is vmx_vcpu_block() can still get called first, since
> > the other ones might not get called yet.
> 
> That refers to the first two questions, yet the third (unanswered
> one) was added by me because I anticipated that response. So
> what's wrong with that last option?

Do you mean " Or (maybe in addition to one of these) writing
something sensible in vmx_pi_hooks_assign() before doing the
hook assignments?"?

The problem is you cannot know whether vmx_vcpu_block() is
called before or after the other hooks. And I am wondering
why do you think the current solution is not good.

Thanks,
Feng

> 
> Jan


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