Re: [PATCH v5 09/14] vpci/header: emulate PCI_COMMAND register for guests

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>]

On 02.02.22 15:32, Jan Beulich wrote:
> On 02.02.2022 13:49, Oleksandr Andrushchenko wrote:
>> On 13.01.22 12:50, Roger Pau Monné wrote:
>>> On Thu, Nov 25, 2021 at 01:02:46PM +0200, Oleksandr Andrushchenko wrote:
>>>> --- a/xen/drivers/vpci/header.c
>>>> +++ b/xen/drivers/vpci/header.c
>>>> @@ -491,6 +491,22 @@ static void cmd_write(const struct pci_dev *pdev, 
>>>> unsigned int reg,
>>>>            pci_conf_write16(pdev->sbdf, reg, cmd);
>>>>    }
>>>>    
>>>> +static void guest_cmd_write(const struct pci_dev *pdev, unsigned int reg,
>>>> +                            uint32_t cmd, void *data)
>>>> +{
>>>> +    /* TODO: Add proper emulation for all bits of the command register. */
>>>> +
>>>> +#ifdef CONFIG_HAS_PCI_MSI
>>>> +    if ( pdev->vpci->msi->enabled )
>>> You need to check for MSI-X also, pdev->vpci->msix->enabled.
>> Indeed, thank you
>>>> +    {
>>>> +        /* Guest wants to enable INTx. It can't be enabled if MSI/MSI-X 
>>>> enabled. */
>>>> +        cmd |= PCI_COMMAND_INTX_DISABLE;
>>> You will also need to make sure PCI_COMMAND_INTX_DISABLE is set in the
>>> command register when attempting to enable MSI or MSIX capabilities.
>> Isn't it enough that we just check above if MSI/MSI-X enabled then make
>> sure INTX disabled? I am not following you here on what else needs to
>> be done.
> No, you need to deal with the potentially bad combination on both
> paths - command register writes (here) and MSI/MSI-X control register
> writes (which is what Roger points you at). I would like to suggest
> to consider simply forcing INTX_DISABLE on behind the guest's back
> for those other two paths.
Do you suggest that we need to have some code which will
write PCI_COMMAND while we write MSI/MSI-X control register
for that kind of consistency? E.g. control register handler will
need to write to PCI_COMMAND and go through emulation for
guests?

If so, why didn't we have that before?
If it was ok before, then I guess the code I add does ensure INTX
is set if pdev->vpci->msi->enabled || pdev->vpci->msix->enabled
which is enough at least for PCI_COMMAND writes.

Sorry if I still didn't get to the point how to do that
>
> Jan
>
Thank you,
Oleksandr