Re: [RFC PATCH v2 3/6] cxl/core: add report option for cxl_mem_get_poison()

[Shiyang Ruan]

在 2024/3/30 9:50, Dan Williams 写道:
> Shiyang Ruan wrote:
> > The GMER only has "Physical Address" field, no such one indicates length.
> > So, when a poison event is received, we could use GET_POISON_LIST command
> > to get the poison list.  Now driver has cxl_mem_get_poison(), so
> > reuse it and add a parameter 'bool report', report poison record to MCE
> > if set true.
>
> I am not sure I agree with the rationale here because there is no
> correlation between the event being signaled and the current state of
> the poison list. It also establishes race between multiple GMER events,
> i.e. imagine the hardware sends 4 GMER events to communicate a 256B
> poison discovery event. Does the driver need logic to support GMER event
> 2, 3, and 4 if it already say all 256B of poison after processing GMER
> event 1?

Yes, I didn't thought about that.

> I think the best the driver can do is assume at least 64B of poison
> per-event and depend on multiple notifications to handle larger poison
> lengths.

Agree.  This also makes things easier.

And for qemu, I'm thinking of making a patch to limit the length of a 
poison record when injecting.  The length should between 64B to 4KiB per 
GMER. And emit many GMERs if length > 4KiB.

> Otherwise, the poison list is really only useful for pre-populating
> pages to offline after a reboot, i.e. to catch the kernel up with the
> state of poison pages after a reboot.

Got it.


--
Thanks,
Ruan.