Re: [Xen-devel] [PATCH 2/3] VT-d: correct dma_msi_set_affinity()

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Friday, December 09, 2016 4:47 PM
> 
> >>> On 08.12.16 at 18:33, <andrew.cooper3@xxxxxxxxxx> wrote:
> > On 08/12/16 16:01, Jan Beulich wrote:
> >> That commit ("VT-d: use msi_compose_msg()) together with 15aa6c6748
> >
> > Which commit?
> 
> Oops - initially I had intended the title to include the hash: 83cd2038fe.
> I've adjusted the text.
> 
> >> ("amd iommu: use base platform MSI implementation") introducing the use
> >> of a per-CPU scratch CPU mask went too far: dma_msi_set_affinity() may,
> >> at least in theory, be called in interrupt context, and hence the use
> >> of that scratch variable is not correct.
> >>
> >> Since the function overwrites the destination information anyway,
> >> allow msi_compose_msg() to be called with a NULL CPU mask, avoiding the
> >> use of that scratch variable.
> >
> > Which function overwrites what?  I can't see dma_msi_set_affinity()
> > doing anything to clobber msg.dest32, so I don't understand why this
> > change is correct.
> 
> msg.dest32 simply isn't being used. msg is local to that function, so
> all that matters is which fields the function consumes. Is uses only
> address and data, and updates address to properly specify the
> intended destination. To guard against stale data (in
> iommu->msi.msg), it may be reasonable to nevertheless set dest32
> before storing msg into that field.
> 

So do you plan to send v2 or stick with current version?

Thanks
Kevin

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