Re: [Xen-devel] [PATCH] x86/HVM: p2m_ram_ro is incompatible with device pass-through

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.05.19 at 14:59, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 02/05/2019 13:29, Jan Beulich wrote:
>> --- a/xen/drivers/passthrough/pci.c
>> +++ b/xen/drivers/passthrough/pci.c
>> @@ -1450,17 +1450,36 @@ static int assign_device(struct domain *
>>      if ( !iommu_enabled || !hd->platform_ops )
>>          return 0;
>>  
>> -    /* Prevent device assign if mem paging or mem sharing have been 
>> -     * enabled for this domain */
>> -    if ( unlikely(d->arch.hvm.mem_sharing_enabled ||
>> -                  vm_event_check_ring(d->vm_event_paging) ||
>> +    domain_lock(d);
>> +
>> +    /*
>> +     * Prevent device assignment if any of
>> +     * - mem paging
>> +     * - mem sharing
>> +     * - the p2m_ram_ro type
>> +     * - global log-dirty mode
> 
> XenServer has working live migration with GPUs, which this change would
> regress.
> 
> Behind the scenes, we combine Xen's logdirty bitmap with one provided by
> the GPU, to ensure that all dirty updates are tracked.

But this says nothing for the patch here. As long as it doesn't
work in the staging tree, it should be prevented. In XenServer
you could then patch out that check and comment line together
with whatever other changes you have to make for thins to
work. Alternatively you could submit a patch (or more) to make
it work in staging too, at which point I'd have to re-base the
one here.

Jan



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