Re: [Xen-devel] [PATCH v3] passthrough/vtd: Don't DMA to the stack in queue_invalidate_wait()

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

> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> Sent: Wednesday, July 17, 2019 12:24 AM
> 
> DMA-ing to the stack is considered bad practice.  In this case, if a
> timeout occurs because of a sluggish device which is processing the
> request, the completion notification will corrupt the stack of a
> subsequent deeper call tree.
> 
> Place the poll_slot in a percpu area and DMA to that instead.
> 
> Fix the declaration of saddr in struct qinval_entry, to avoid a shift by
> two.  The requirement here is that the DMA address is dword aligned,
> which is covered by poll_slot's type.
> 
> This change does not address other issues.  Correlating completions
> after a timeout with their request is a more complicated change.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>

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