Re: [Xen-devel] [PATCH 1/4] x86/vMSI-X: defer intercept handler registration

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.06.16 at 18:13, <konrad.wilk@xxxxxxxxxx> wrote:
> On Wed, Jun 08, 2016 at 06:52:58AM -0600, Jan Beulich wrote:
>> There's no point in registering the internal MSI-X table intercept
>> functions on all domains - it is sufficient to do so once a domain gets
>> an MSI-X capable device assigned.
> 
> I think this will break on SR-IOV devices that are created and we
> had not setup MCFG.

How does MCFG get into the picture here? (And anyway, this series
is about vMSI-X, not host MSI-X.)

> There is this Intel board (which I have) where the MCFG is setup
> only via ACPI and in the past we had issues - where we never
> detect that the VF had MSI-X - b/c we could not access the
> configuration registers past 0xff.

The MSI-X capability necessarily lives in the low 256 bytes. Do you
mean the SR-IOV capability?

> I am pretty sure that Linux now uploads the MCFG data during
> bootup from the ACPI AML code, but earlier kernels may not.
> 
> And that would mean the device would try to use MSI-X while
> code would be !pdev->msix.
> 
> Hmm, thought I wonder - with all those improvements of capturing
> the MSI-X and validating it in the hypervisor - would this
> even matter?
> 
> Let me stash an 82576 card in that box and see what happens with
> Xen 4.7.

Thanks.

Jan


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