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Re: [PATCH v6 10/13] vpci/header: reset the command register when adding devices
- To: Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 7 Feb 2022 16:28:43 +0100
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- Cc: "julien@xxxxxxx" <julien@xxxxxxx>, "sstabellini@xxxxxxxxxx" <sstabellini@xxxxxxxxxx>, Oleksandr Tyshchenko <Oleksandr_Tyshchenko@xxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Artem Mygaiev <Artem_Mygaiev@xxxxxxxx>, "roger.pau@xxxxxxxxxx" <roger.pau@xxxxxxxxxx>, "andrew.cooper3@xxxxxxxxxx" <andrew.cooper3@xxxxxxxxxx>, "george.dunlap@xxxxxxxxxx" <george.dunlap@xxxxxxxxxx>, "paul@xxxxxxx" <paul@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Rahul Singh <rahul.singh@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 07 Feb 2022 15:28:56 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 07.02.2022 16:14, Oleksandr Andrushchenko wrote:
> On 07.02.22 17:05, Jan Beulich wrote:
>> On 07.02.2022 15:46, Oleksandr Andrushchenko wrote:
>>> On 07.02.22 16:31, Jan Beulich wrote:
>>>> But: What's still missing here then is the separation of guest and host
>>>> views. When we set INTx behind the guest's back, it shouldn't observe the
>>>> bit set. Or is this meant to be another (big) TODO?
>>> But, patch [PATCH v6 09/13] vpci/header: emulate PCI_COMMAND register for
>>> guests
>>> already takes care of it, I mean that it will set/reset INTx for the guest
>>> according to MSI/MSI-X. So, if we squash these two patches the whole
>>> picture will be seen at once.
>> Does it? I did get the impression that the guest would be able to observe
>> the bit set even after writing zero to it (while a reason exists that Xen
>> wants the bit set).
> Yes, you are correct: guest might not see what it wanted to set.
> I meant that Xen won't allow resetting INTx if it is not possible
> due to MSI/MSI-X
>
> Anyways, I think squashing will be a good idea to have the relevant
> functionality in a single change set. Will this work for you?
It might work, but I'd prefer things which can sensibly be separate to
remain separate.
Jan
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