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Re: [Xen-devel] [PATCH v5 5/6] xen/x86: add PHYSDEVOP_msi_control
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <JBeulich@xxxxxxxx>
- Date: Fri, 19 Jul 2019 08:04:45 +0000
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, AndrewCooper <andrew.cooper3@xxxxxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, TimDeegan <tim@xxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
- Delivery-date: Fri, 19 Jul 2019 08:07:58 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [PATCH v5 5/6] xen/x86: add PHYSDEVOP_msi_control
On 18.07.2019 18:52, Roger Pau Monné wrote:
> On Thu, Jul 18, 2019 at 03:17:27PM +0000, Jan Beulich wrote:
>> On 18.07.2019 15:46, Roger Pau Monné wrote:
>>> In fact I don't think INTx should be enabled when MSI(-X) is disabled,
>>> QEMU already traps writes to the command register, and it will manage
>>> INTx enabling/disabling by itself. I think the only check required is
>>> that MSI(-X) cannot be enabled if INTx is also enabled. In the same
>>> way both MSI caspabilities cannot be enabled simultaneously. The
>>> function should not explicitly disable any of the other capabilities,
>>> and just return -EBUSY if the caller attempts for example to enable
>>> MSI while INTx or MSI-X is enabled.
>>
>> You do realize that pci_intx() only ever gets called for Xen
>> internally used interrupts, i.e. mainly the serial console one?
>
> You will have to bear with me because I'm not sure I understand why
> it does matter. Do you mean to point out that dom0 is the one in full
> control of INTx, and thus Xen shouldn't care of whether INTx and
> MSI(-X) are enabled at the same time?
>
> I still think that at least a warning should be printed if a caller
> tries to enable MSI(-X) while INTx is also enabled, but unless there's
> a reason to have both MSI(-X) and INTx enabled at the same time (maybe
> a quirk for some hardware issue?) it shouldn't be allowed on this new
> interface.
I don't mind improvements to the current situation (i.e. such a
warning may indeed make sense); I merely stated how things currently
are. INTx treatment was completely left aside when MSI support was
introduced into Xen.
Jan
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