Re: [RFD] x86/split_lock: Request to Intel

Xiaoyao Li
2019-10-18T04:58:05Z

On 10/17/2019 8:29 PM, Thomas Gleixner wrote:
> The more I look at this trainwreck, the less interested I am in merging any
> of this at all.
>
> The fact that it took Intel more than a year to figure out that the MSR is
> per core and not per thread is yet another proof that this industry just
> works by pure chance.
>

Whether it's per-core or per-thread doesn't affect much how we implement
for host/native.

And also, no matter it's per-core or per-thread, we always can do
something in VIRT.

Maybe what matters is below.

> Seriously, this makes only sense when it's by default enabled and not
> rendered useless by VIRT. Otherwise we never get any reports and none of
> the issues are going to be fixed.
>

For VIRT, it doesn't want old guest to be killed due to #AC. But for
native, it doesn't want VIRT to disable the #AC detection

I think it's just about the default behavior that whether to disable the
host's #AC detection or kill the guest (SIGBUS or something else) once
there is an split-lock #AC in guest.

So we can provide CONFIG option to set the default behavior and module
parameter to let KVM set/change the default behavior.