Re: [PART1 RFC v3 12/12] svm: Manage vcpu load/unload when enable AVIC

Suravee Suthikulpanit
2016-03-31T08:53:08Z

Hi Radim,

On 03/19/2016 04:44 AM, Radim Krčmář wrote:
> 2016-03-18 01:09-0500, Suravee Suthikulpanit:
>> From: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
>> +
>> + WRITE_ONCE(*entry, new_entry);
>
> This will translate to two writes in 32 bit mode and we need to write
> physical ID first to avoid spurious doorbells ...
> is the order guaranteed?

Hm.. not sure on that.

>> + } else {
>> + new_entry = READ_ONCE(*entry);
>> + /**
>> + * This handles the case when vcpu is scheduled out
>> + * and has not yet not called blocking. We save the
>> + * AVIC running flag so that we can restore later.
>> + */
>
> is_running must be disabled in between ...blocking and ...unblocking,
> because we don't want to miss interrupts and block forever.
> I somehow don't get it from the comment. :)

Not sure if I understand your concern. However, the is_running bit
setting/clearing should be handled in the avic_set_running below. This
part only handles othe case when the is_running bit still set when
calling vcpu_put (and later on loading some other vcpus). This way, when
we are re-loading this vcpu, we can restore the is_running bit accordingly.

Thanks,
Suravee