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Re: [RFC XEN PATCH 2/6] vpci: accept BAR writes if dom0 is PVH
- To: Huang Rui <ray.huang@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 21 Mar 2023 10:41:57 +0100
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- Cc: "Deucher, Alexander" <Alexander.Deucher@xxxxxxx>, "Koenig, Christian" <Christian.Koenig@xxxxxxx>, "Hildebrand, Stewart" <Stewart.Hildebrand@xxxxxxx>, Xenia Ragiadakou <burzalodowa@xxxxxxxxx>, "Huang, Honglei1" <Honglei1.Huang@xxxxxxx>, "Zhang, Julia" <Julia.Zhang@xxxxxxx>, "Chen, Jiqian" <Jiqian.Chen@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 21 Mar 2023 09:42:17 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 21.03.2023 10:36, Huang Rui wrote:
> On Wed, Mar 15, 2023 at 12:02:35AM +0800, Jan Beulich wrote:
>> On 12.03.2023 08:54, Huang Rui wrote:
>>> --- a/xen/drivers/vpci/header.c
>>> +++ b/xen/drivers/vpci/header.c
>>> @@ -392,7 +392,7 @@ static void cf_check bar_write(
>>> * Xen only cares whether the BAR is mapped into the p2m, so allow BAR
>>> * writes as long as the BAR is not mapped into the p2m.
>>> */
>>> - if ( bar->enabled )
>>> + if ( pci_conf_read16(pdev->sbdf, PCI_COMMAND) & PCI_COMMAND_MEMORY )
>>> {
>>> /* If the value written is the current one avoid printing a
>>> warning. */
>>> if ( val != (uint32_t)(bar->addr >> (hi ? 32 : 0)) )
>>
>> ... bar->enabled doesn't properly reflect the necessary state? It
>> generally shouldn't be necessary to look at the physical device's
>> state here.
>>
>> Furthermore when you make a change in a case like this, the
>> accompanying comment also needs updating (which might have clarified
>> what, if anything, has been wrong).
>>
>
> That is the problem that we start domU at the first time, the enable flag
> will be set while the passthrough device would like to write the real pcie
> bar on the host.
A pass-through device (i.e. one already owned by a DomU) should never
be allowed to write to the real BAR. But it's not clear whether I'm not
misinterpreting what you said ...
> And yes, it's temporary workaround, we should figure out
> the root cause.
Right, that's the only way to approach this, imo.
Jan
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