Re: [Xen-devel] [PATCH v2] xen/pt: fix some pass-thru devices don't work across reboot

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.11.18 at 02:10, <chao.gao@xxxxxxxxx> wrote:
> I find some pass-thru devices don't work any more across guest
> reboot. Assigning it to another domain also meets the same issue. And
> the only way to make it work again is un-binding and binding it to
> pciback. Someone reported this issue one year ago [1].
> 
> If the device's driver doesn't disable MSI-X during shutdown or qemu is
> killed/crashed before the domain shutdown, this domain's pirq won't be
> unmapped. Then xen will unmap all pirq. But pciback has already disabled
> meory decoding before xen unmapping pirq. Then when Xen is disabling a
> MSI of the device, it has to sets the host_maskall flag and maskall bit
> to mask a MSI rather than sets maskbit in MSI-x table. The call trace of
> this process is:
> ->arch_domain_destroy
>     ->free_domain_pirqs
>         ->unmap_domain_pirq (if pirq isn't unmap by qemu)
>             ->pirq_guest_force_unbind
>                 ->__pirq_guest_unbind
>                     ->mask_msi_irq(=desc->handler->disable())
>                         ->the warning in msi_set_mask_bit()
> 
> The host_maskall bit will prevent guests from clearing the maskall bit
> even the device is assigned to another guest later. Guests cannot
> receive interrupts from this device.
> 
> To fix this, host_maskall flag is cleared when all MSIs of a device are 
> freed.
> It is definitely safely to clear it because no msi is actually set up
> for this device. Also, 'msix->warned' is initialized to DOMID_INVALID
> rather than 0 to avoid warnings missing for Dom0.
> 
> [1]: 
> https://lists.xenproject.org/archives/html/xen-devel/2017-09/msg02520.html 
> 
> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>

So I take it this patch has become obsolete with the xen-pciback
change you've posted a few days ago?

Jan



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