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

From: Xiaoyao Li
Date: Fri Oct 18 2019 - 00:58:04 EST

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.