Re: [Xen-devel] [PATCH for-4.10 v2] passthrough/vtd: Don't DMA to the stack in queue_invalidate_wait()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.10.17 at 18:22, <andrew.cooper3@xxxxxxxxxx> wrote:
> DMA-ing to the stack is generally 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.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Please could you extend the commit message to state the issue
remaining with using a single per-CPU slot? With that
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
albeit ...

> @@ -167,7 +169,7 @@ static int __must_check queue_invalidate_wait(struct 
> iommu *iommu,
>      qinval_entry->q.inv_wait_dsc.lo.res_1 = 0;
>      qinval_entry->q.inv_wait_dsc.lo.sdata = QINVAL_STAT_DONE;
>      qinval_entry->q.inv_wait_dsc.hi.res_1 = 0;
> -    qinval_entry->q.inv_wait_dsc.hi.saddr = virt_to_maddr(&poll_slot) >> 2;
> +    qinval_entry->q.inv_wait_dsc.hi.saddr = virt_to_maddr(this_poll_slot) >> 
> 2;

... this one is still a literal number rather than something allowing
to associate back where that value is coming from (but since you're
not introducing it here, I also won't insist on you changing it in this
patch).

Jan


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