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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

Jan