linux-kernel - Re: [Xen-devel] [PATCH 2/3 v3] Refactor MSI restore call-chain to drop unnecessary argument

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Message-Id: <521F42CD02000078000EF5D0@nat28.tlf.novell.com>
Date:	Thu, 29 Aug 2013 11:47:09 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	<zhenzhong.duan@...cle.com>
Cc:	"Bjorn Helgaas" <bhelgaas@...gle.com>,
	"xen-devel" <xen-devel@...ts.xenproject.org>,
	"Feng Jin" <joe.jin@...cle.com>,
	"Sucheta Chakraborty" <sucheta.chakraborty@...gic.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 2/3 v3] Refactor MSI restore call-chain
 to drop unnecessary argument

>>> On 29.08.13 at 11:50, Zhenzhong Duan <zhenzhong.duan@...cle.com> wrote:

> On 2013-08-29 15:23, Jan Beulich wrote:
>>>>> On 29.08.13 at 04:52, Zhenzhong Duan <zhenzhong.duan@...cle.com> wrote:
>>> But in initial domain (aka priviliged guest), it's different.
>>> Driver init call graph under initial domain:
>>> driver_init->
>>>      msix_capability_init->
>>>          msix_program_entries->
>>>              msix_mask_irq->
>>>                  entry->masked = 1
>>>      request_irq->
>>>          __setup_irq->
>>>              irq_startup->
>>>                  __startup_pirq->
>>>                      EVTCHNOP_bind_pirq hypercall    (trap into Xen)
>>> [Xen:]
>>> pirq_guest_bind->
>>>      startup_msi_irq->
>>>          unmask_msi_irq->
>>>              msi_set_mask_bit->
>>>                  entry->msi_attrib.masked = 0
>>>
>>> So entry->msi_attrib.masked in xen side always has newest value. entry->masked
>>> in initial domain is untouched and is 1 after msix_capability_init.
>> And as said several times before - Linux shouldn't be touching
>> the MSI-X table at all during initial setup or resume (it should in
>> particular not rely on such accesses to not fault, as being a
>> privilege violation); all it needs to do is update its software state.
> My patch just remove access to msix mask register in dom0. Anything 
> wrong with that?

Oh, okay, I mis-read the change then - you're moving the mask
bit changing from __pci_restore_msi{,x}_state() to
default_restore_msi_irqs(). Which of course is fine if Xen (as you
say) doesn't use the latter.

Sorry for the noise then,
Jan

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