On 5/1/2023 10:51 PM, Sean Christopherson wrote:
For the NX hugepage mitation, I think it makes sense to restart the discussion
in the context of this thread: https://lore.kernel.org/all/ZBxf+ewCimtHY2XO@xxxxxxxxxx
OK, wasn't aware of that thread. Thanks for pointing out.
Just took a glance at it, I'll comment there.
TL;DR: I am open to providng an option to hard disable the mitigation,
Why hard disable? Isn't already "nx_huge_pages" parameter sufficient for this?
My aforementioned not-sent-out patch is to consider nx_huge_pages for
creating the kthread or not, i.e. if nx_huge is enabled, start the kthread,
if not, terminate the kthread; once re-enabled, spawn the kthread again...
but there
needs to be sufficient justification, e.g. that the above 100ms latency is a
problem for real world deployments.
Ah, I was objected by similar reason: the kthread does nothing if
nx_huge_pages = false, it does no harm. Therefore I put the patch aside.
For the justification from real world, I guess Zhuangel570 can say more.
As more and more old CPUs retires, I think NX-HugePage code will become more
and more minority code path/situation, and be refactored out eventually one
day.
Heh, yeah, one day. But "one day" is likely 10+ years away. Intel discontinuing
a CPU has practically zero relevance to KVM removing support a CPU, e.g. KVM still
supports the original Core CPUs from ~2006, which were launched in 2006 and
discontinued in 2008.
OK, got it.
Why does KVM still FULLY support so old CPUs? Any real world users? What's
the rational/necessity? even if it's already EOL by manufacture.
My thought was that each new generation of CPU will linger in CSP's data
center for 3~4 yrs.
