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Re: [Xen-devel] [PATCH] x86/HVM: p2m_ram_ro is incompatible with device pass-through
- To: Jan Beulich <JBeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 2 May 2019 14:42:10 +0100
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- Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Paul Durrant <paul.durrant@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 02 May 2019 13:42:15 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 02/05/2019 14:16, Jan Beulich wrote:
>>>> 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.
Yes it does.
There is nothing inherent about global log-dirty mode which is
incompatible with passthrough when the IOMMU pagetables are not shared
with EPT.
> As long as it doesn't work in the staging tree, it should be prevented.
... but it does work.
> 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.
Everything is upstream in the various projects, other than the vendor's
closed source library and kernel driver.
~Andrew
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