From: "Wu, Feng" <feng.wu@intel.com>
To: George Dunlap <George.Dunlap@eu.citrix.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>, Keir Fraser <keir@xen.org>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Dario Faggioli <dario.faggioli@citrix.com>,
"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
Jan Beulich <jbeulich@suse.com>, "Wu, Feng" <feng.wu@intel.com>
Subject: Re: [PATCH v2 3/4] VMX: Assign the right value to 'NDST' field in a concern case
Date: Fri, 24 Jun 2016 09:08:45 +0000 [thread overview]
Message-ID: <E959C4978C3B6342920538CF579893F01972E6E1@SHSMSX103.ccr.corp.intel.com> (raw)
In-Reply-To: <CAFLBxZbk_JyrGsmXmZ10-HmE9xy+188mKN=6qZgiEL3L+_xe8A@mail.gmail.com>
> -----Original Message-----
> From: dunlapg@gmail.com [mailto:dunlapg@gmail.com] On Behalf Of George
> Dunlap
> Sent: Thursday, June 23, 2016 2:01 AM
> To: Wu, Feng <feng.wu@intel.com>
> Cc: xen-devel@lists.xen.org; Tian, Kevin <kevin.tian@intel.com>; Keir Fraser
> <keir@xen.org>; Andrew Cooper <andrew.cooper3@citrix.com>; Dario Faggioli
> <dario.faggioli@citrix.com>; Jan Beulich <jbeulich@suse.com>
> Subject: Re: [Xen-devel] [PATCH v2 3/4] VMX: Assign the right value to 'NDST'
> field in a concern case
>
> On Thu, May 26, 2016 at 2:39 PM, Feng Wu <feng.wu@intel.com> 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.
> >
> > This patch fix this concern case.
> >
> > Signed-off-by: Feng Wu <feng.wu@intel.com>
>
> I agree with Jan that a cleaner solution here would be making sure
> that all the appropriate state is actually set up for all vcpus before
> leaving vmx_pi_hooks_assign(). With the patch you propose, the
> following sequence of events is possible:
>
> * vcpu 0 starts running on a pcpu
> * a device is assigned, causing the hooks to be set
> * an interrupt from the device is routed to vcpu 0, but it is not
> actually delivered properly, since ndst is not pointing to the right
> processor.
>
> One option would be to pause all vcpus before setting the hooks and
> then un-pause them; this would force all the vcpus to go through
> vmx_pi_switch_to() before vmx_vcpu_block(). Another would be to grab
> the scheduler lock for each pcpu and write the vcpu's ndst with the
> appropriate value before setting the hooks.
That sounds a great idea. Besides that, maybe we can also pause/unpause
the domain before/after unsetting the hooks, then we don't need to
care about the race condition when vmx_pi_hooks_deassign() and
vmx_vcpu_block() get called at the same time. After unpause the domain,
we can safely remove the vCPUs from the per-cpu blocking list if needed.
Thanks,
Feng
>
> -George
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next prev parent reply other threads:[~2016-06-24 9:08 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-26 13:39 [PATCH v2 0/4] VMX: Properly handle pi descriptor and per-cpu blocking list Feng Wu
2016-05-26 13:39 ` [PATCH v2 1/4] VMX: Properly handle pi when all the assigned devices are removed Feng Wu
2016-05-27 13:43 ` Jan Beulich
2016-05-31 10:22 ` Wu, Feng
2016-05-31 11:52 ` Jan Beulich
2016-06-03 5:12 ` Wu, Feng
2016-06-03 9:45 ` Jan Beulich
2016-05-26 13:39 ` [PATCH v2 2/4] VMX: Cleanup PI per-cpu blocking list when vcpu is destroyed Feng Wu
2016-05-27 13:49 ` Jan Beulich
2016-05-31 10:22 ` Wu, Feng
2016-05-31 11:54 ` Jan Beulich
2016-05-26 13:39 ` [PATCH v2 3/4] VMX: Assign the right value to 'NDST' field in a concern case Feng Wu
2016-05-27 14:00 ` Jan Beulich
2016-05-31 10:27 ` Wu, Feng
2016-05-31 11:58 ` Jan Beulich
2016-06-03 5:23 ` Wu, Feng
2016-06-03 9:57 ` Jan Beulich
2016-06-22 18:00 ` George Dunlap
2016-06-24 9:08 ` Wu, Feng [this message]
2016-05-26 13:39 ` [PATCH v2 4/4] VMX: fixup PI descritpor when cpu is offline Feng Wu
2016-05-27 14:56 ` Jan Beulich
2016-05-31 10:31 ` Wu, Feng
2016-06-22 18:33 ` George Dunlap
2016-06-24 6:34 ` Wu, Feng
2016-05-26 17:20 ` [PATCH v2 0/4] VMX: Properly handle pi descriptor and per-cpu blocking list Dario Faggioli
2016-05-31 10:19 ` Wu, Feng
2016-06-22 21:33 ` Dario Faggioli
2016-06-24 6:33 ` Wu, Feng
2016-06-24 10:29 ` Dario Faggioli
2016-06-24 13:42 ` Wu, Feng
2016-06-24 13:49 ` George Dunlap
2016-06-24 14:36 ` Dario Faggioli
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