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

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Date:	Thu, 29 Aug 2013 17:50:38 +0800
From:	Zhenzhong Duan <zhenzhong.duan@...cle.com>
To:	Jan Beulich <JBeulich@...e.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 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?
>
> Hence fiddling with default_restore_msi_irqs() seems the wrong
> approach towards solving the problem.
dom0 uses xen_initdom_restore_msi_irqs, default_restore_msi_irqs is for 
baremetal.

zduan
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