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

From: Suravee Suthikulpanit
Date: Thu Mar 31 2016 - 04:53:12 EST


Hi Radim,

On 03/19/2016 04:44 AM, Radim KrÄmÃÅ wrote:
2016-03-18 01:09-0500, Suravee Suthikulpanit:
From: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
+
+ 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