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

[Chao Gao <chao.gao@intel.com>]

On Tue, Dec 11, 2018 at 10:03:10AM -0700, Jan Beulich wrote:
>>>> On 15.11.18 at 02:10, <chao.gao@intel.com> 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@intel.com>
>
>So I take it this patch has become obsolete with the xen-pciback
>change you've posted a few days ago?

Yes, you are right.

Thanks
Chao

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