On 2021/3/12 17:02, Marc Zyngier wrote:

On Thu, 11 Mar 2021 12:31:48 +0000,
Shenming Lu [off-list ref] wrote:

quoted

On 2021/3/11 17:09, Marc Zyngier wrote:

quoted

quoted

I have asked that question in the past: is it actually safe to remap
the vPEs and expect them to be runnable

In my opinion, logically it can work, but there might be problems like the
one below that I didn't notice...

One thing is that you will have lost interrupts in the meantime
(assuming your devices are still alive). How will you make up for
that?

I think that devices should be paused for (not only) saving interrupt states,
and in fact, that's exactly what such as VFIO devices do...

quoted

quoted

Also, the current code assumes that VMAPP.PTZ can be advertised if a
VPT is mapped for the first time. Clearly, it is unlikely that the VPT
will be only populated with 0s, so you'll end up with state corruption
on the first remap.

Oh, thanks for pointing it out.
And if we always signal PTZ when alloc = 1, does it mean that we
can't remap the vPE when the VPT is not empty, thus there is no
chance to get the VLPI state?  Could we just assume that the VPT is
not empty when first mapping the vPE?

I think we should drop the setting of PTZ altogether. It is a silly
micro-optimisation, and if the HW can't parse the VPT efficiently when
it is empty, then the HW is pretty bad, PTZ or not.

agree :-)

Thanks,
Shenming

Thanks,

	M.

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