Re: [Xen-devel] [PATCH v14 4/9] iommu: don't domain_crash() inside iommu_map/unmap_page()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.10.18 at 12:38, <Paul.Durrant@xxxxxxxxxx> wrote:
>> From: George Dunlap
>> Sent: 05 October 2018 11:35
>> 
>> > On Oct 5, 2018, at 11:27 AM, Paul Durrant <Paul.Durrant@xxxxxxxxxx>
>> wrote:
>> > But for mapping too? It seems unnecessary to crash the domain in that
>> case.
>> 
>> ISTR that the domain_crash() was added only a few years ago; I’d have to
>> go back and see the reasoning for it being added in the first place.  I’ll
>> do that Monday if Jan doesn’t beat me to it.
>> 
> 
> I was added by the following commit:
> 
> commit 834c97baebb3743c54bcae228e984ae1b9692e6a
> Author: Quan Xu <quan.xu@xxxxxxxxx>
> Date:   Tue Jun 14 15:10:57 2016 +0200
> 
>     IOMMU: handle IOMMU mapping and unmapping failures
> 
>     Treat IOMMU mapping and unmapping failures as a fatal to the DomU
>     If IOMMU mapping and unmapping failed, crash the DomU and propagate
>     the error up to the call trees.
> 
>     No spamming of the log can occur. For DomU, we avoid logging any
>     message for already dying domains. For Dom0, that'll still be more
>     verbose than we'd really like, but it at least wouldn't outright
>     flood the console.
> 
>     Signed-off-by: Quan Xu <quan.xu@xxxxxxxxx>
>     Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
>     Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> So the justification appears to be to avoid log spam.

Iirc that part of the description only exists because early version of
that patch did introduce log spam.

The problem iirc is mainly proper error handling, in particular proper
unwinding of earlier mappings that may have got installed
successfully in the context of the same hypercall (or whatever).

Jan


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