Re: [PATCH v9 15/17] vmx: VT-d posted-interrupt core logic handling

From: Dario Faggioli <dario.faggioli@citrix.com>
To: "Wu, Feng" <feng.wu@intel.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Cc: George Dunlap <george.dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	"Tian, Kevin" <kevin.tian@intel.com>, Keir Fraser <keir@xen.org>,
	Jan Beulich <jbeulich@suse.com>
Subject: Re: [PATCH v9 15/17] vmx: VT-d posted-interrupt core logic handling
Date: Wed, 11 Nov 2015 15:46:39 +0100	[thread overview]
Message-ID: <1447253199.2767.5.camel@citrix.com> (raw)
In-Reply-To: <E959C4978C3B6342920538CF579893F00AE54397@SHSMSX104.ccr.corp.intel.com>

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On Wed, 2015-11-11 at 13:29 +0000, Wu, Feng wrote:
> 
> > -----Original Message-----
> > From: Wu, Feng

> > Yes, that is the case, after arch_vcpu_block() is called, we don't
> > cancel it even if there are events to be delivered, so we need to
> > check
> > whether the NV is the right value, if it isn't, which means after
> > after arch_vcpu_block(),local_events_need_delivery() check returns
> > true, so we need to adjust the PI state before VM-Entry. As Jan
> > mentioned
> > before, we will check the value before actually update it
> > atomically, so
> > I think it is okay from performance point of view.
> 
> Besides the case you mentioned above, it also covers another case:
> now
> we remove the arch hook in vcpu_wake(), so when vCPU is woken up,
> the 'NV' filed is still 'wakeup_vector', hence we need to recover it
> before
> VM Entry.
> 
Well, sure. That, however, could have been handled by having this code
called from vmx_do_resume(), I think.

In fact, waking up certainly calls for the descriptor to be updated,
but it also involves scheduling (well, at least starting executing
after a wakeup does). So schedule_tail(), and hence vmx_do_resume(),
would at some point be involved.

My question above was about confirming that the (only) reason why you
need that code in vmx_enter_helper() rather than in vmx_do_resume() was
the 'block cancellation issue', not about why you need to change the PI
control block at all. :-)

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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