On Mon, Sep 18 2023 at 20:37, Jason Gunthorpe wrote:
> On Mon, Sep 18, 2023 at 08:43:21PM +0200, Thomas Gleixner wrote:
>> On Mon, Sep 18 2023 at 11:17, Jason Gunthorpe wrote:
>> > On Thu, Sep 14, 2023 at 12:14:06PM -0700, Shannon Nelson wrote:
>> >> The new MSI dynamic allocation machinery is great for making the irq
>> >> management more flexible. It includes caching information about the
>> >> MSI domain which gets reused on each new open of a VFIO fd. However,
>> >> this causes an issue when the underlying hardware has flexible MSI-x
>> >> configurations, as a changed configuration doesn't get seen between
>> >> new opens, and is only refreshed between PCI unbind/bind cycles.
>> >>
>> >> In our device we can change the per-VF MSI-x resource allocation
>> >> without the need for rebooting or function reset. For example,
>> >>
>> >> 1. Initial power up and kernel boot:
>> >> # lspci -s 2e:00.1 -vv | grep MSI-X
>> >> Capabilities: [a0] MSI-X: Enable+ Count=8 Masked-
>> >>
>> >> 2. Device VF configuration change happens with no reset
>> >
>> > Is this an out of tree driver problem?
>> >
>> > The intree way to alter the MSI configuration is via
>> > sriov_set_msix_vec_count, and there is only one in-tree driver that
>> > uses it right now.
>>
>> Right, but that only addresses the driver specific issues.
>
> Sort of.. sriov_vf_msix_count_store() is intended to be the entry
> point for this and if the kernel grows places that cache the value or
> something then this function should flush those caches too.
Sorry. What I wanted to say is that the driver callback is not the right
place to reload the MSI domains after the change.
> I suppose flushing happens implicitly because Shannon reports that
> things work fine if the driver is rebound. Since
> sriov_vf_msix_count_store() ensures there is no driver bound before
> proceeding it probe/unprobe must be flushing out everything?
Correct. So sriov_set_msix_vec_count() could just do:
ret = pdev->driver->sriov_set_msix_vec_count(vf_dev, val);
if (!ret)
teardown_msi_domain(pdev);
Right?
Thanks,
tglx
