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Re: [PATCH v5 08/11] xen/arm: Enable the existing x86 virtual PCI support for ARM.

  • To: Stefano Stabellini <sstabellini@xxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Tue, 12 Oct 2021 10:04:47 +0200
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  • Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Rahul Singh <Rahul.Singh@xxxxxxx>, Andre Przywara <Andre.Przywara@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Paul Durrant <paul@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Tue, 12 Oct 2021 08:05:02 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 11.10.2021 20:18, Stefano Stabellini wrote:
> On Mon, 11 Oct 2021, Jan Beulich wrote:
>> On 11.10.2021 15:34, Bertrand Marquis wrote:
>>>> On 11 Oct 2021, at 14:09, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>>> On 11.10.2021 14:41, Bertrand Marquis wrote:
>>>>> But digging deeper into this, I would have 2 questions:
>>>>> - msi_cleanup was done there after a request from Stefano, but is not
>>>>> done in case or iommu error, is there an issue to solve here ?
>>>> Maybe, but I'm not sure. This very much depends on what a domain
>>>> could in principle do with a partly set-up device. Plus let's
>>>> not forget that we're talking of only Dom0 here (for now at least,
>>>> i.e. not considering the dom0less case).
>>>> But I'd also like to further defer to Stefano.
>>> Ok, I must admit I do not really see at that stage why doing an MSI cleanup
>>> could be needed so I will wait for Stefano to know if I need to keep this 
>>> when
>>> moving the block up (at the end it is theoretical right now as this is 
>>> empty).
> I know that MSIs are not supported yet on ARM (pci_cleanup_msi does
> nothing). But I wanted to make sure that the pci_cleanup_msi() calls are
> present anywhere necessary, especially on the error paths. So that once
> we add MSI support, we don't need to search through the code to find all
> the error paths missing a pci_cleanup_msi() call.
> To answer your first question: you are right, we are also missing a
> pci_cleanup_msi() call in the case of IOMMU error. So it might be better
> to move the call to pci_cleanup_msi() under the "out" label so that we
> can do it once for both cases.
> To answer your second point about whether it is necessary at all: if
> MSIs and MSI-Xs cannot be already setup at this point at all (not even
> the enable bit), then we don't need any call to pci_cleanup_msi() in
> pci_add_device.

Well, at the very least MSI can't be set up ahead of the traps getting
put in place. Whether partial success of putting traps in place may
allow a cunning guest to set up MSI may depend on further aspects.




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