On Fri, Nov 20, 2015 at 4:54 AM, Alex Williamson
<alex.williamson@xxxxxxxxxx> wrote:
> On Sat, 2015-11-14 at 14:06 +0530, Shivaprasad G Bhat wrote:
>> Before unbind from stub driver libvirt should be sure the guest is not using
>> the device anymore. The libvirt today waits for pci-stub driver alone in /proc/iommu.
>> The same wait is needed for vfio devices too.
>>
>> Signed-off-by: Shivaprasad G Bhat <sbhat@xxxxxxxxxxxxxxxxxx>
>> ---
>> src/util/virhostdev.c | 7 +++++++
>> 1 file changed, 7 insertions(+)
>>
>> diff --git a/src/util/virhostdev.c b/src/util/virhostdev.c
>> index f24ccd8..9f15f34 100644
>> --- a/src/util/virhostdev.c
>> +++ b/src/util/virhostdev.c
>> @@ -756,6 +756,13 @@ virHostdevReattachPCIDevice(virPCIDevicePtr dev, virHostdevManagerPtr mgr)
>> usleep(100*1000);
>> retries--;
>> }
>> + } else if (STREQ(virPCIDeviceGetStubDriver(dev), "vfio-pci")) {
>> + int retries = 100;
>> + while (virPCIDeviceWaitForCleanup(dev, "vfio-pci")
>> + && retries) {
>> + usleep(100*1000);
>> + retries--;
>> + }
>> }
>>
>> if (virPCIDeviceReattach(dev, mgr->activePCIHostdevs,
>
> Hi,
>
> Laine pointed out this patch to me, and it seems entirely unnecessary.
> Can you explain what it fixes?
>
> The reason that pci-stub and legacy KVM device assignment needs to do
> this little delay is because pci-stub itself is not in control of the
> device, it will happily release the device at any point in time,
> regardless of whether KVM is still making use of it. With vfio-pci, all
> the device access occurs through the vfio-pci driver, so you can be sure
> that if the vfio-pci driver unbinds from the device it is unused. In
> fact, the unbind will block until it is unused.
>
Hi Alex,
Thanks for taking a look.
I didn't want to leave out any case where the host crash would occur because
of early release of the device. I could see the /dev/iommu reporting
the vfio-pci
using the device when the guest is actually using it. The behavior of vfio-pci
that you mentioned, is it true across architectures? If yes, we can confidently
drop this wait.
Thanks,
Shivaprasad
>
> Are you doing this to make sure you don't get stuck in that blocked
> unbind and trigger an eject request to the guest? It certainly needs an
> explanation beyond pci-stub did this, so we should too. Thanks,
>
> Alex
>
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