Re: [Xen-devel] [PATCH v2] x86/hvmloader: round up memory BAR size to 4K

[Jan Beulich <jbeulich@xxxxxxxx>]

On 22.01.2020 15:04, Jason Andryuk wrote:
> On Wed, Jan 22, 2020 at 5:52 AM Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
>> On Wed, Jan 22, 2020 at 11:27:24AM +0100, Jan Beulich wrote:
>>> On 21.01.2020 17:57, Roger Pau Monné wrote:
>>>> Ie: Xen should refuse to pass through any memory BAR that's not page
>>>> aligned. How the alignment is accomplished is out of the scope to Xen,
>>>> as long as memory BARs are aligned.
>>>
>>> That's an acceptable model, as long as it wouldn't typically break
>>> existing configurations, and as long as for those who we would
>>> break there are easy to follow steps to unbreak their setups.
>>
>> Jason, do you think you could take a stab at adding a check in order
>> to make sure memory BAR addresses are 4K aligned when assigning a
>> device to a guest?
> 
> I can take a look.  You want the hypervisor to make the enforcement
> and not the toolstack?

Well, if ...

> Waving my hands a little bit, but it might be possible to have `xl
> pci-assignable-add` trigger the linux pci resource_alignment at
> runtime.

... this was possible, then it would be a change to both. Anyway I
think for the purpose of better diagnostics the tool stack should
do the check, but the hypervisor should do so too (as the ultimate
entity wanting this enforced).

Jan

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