Re: [PATCH v3 10/10] x86/split_lock: Handle #AC exception for split lock

From: Ingo Molnar
Date: Wed Feb 13 2019 - 03:14:58 EST

* Fenghua Yu <fenghua.yu@xxxxxxxxx> wrote:

> On Mon, Feb 11, 2019 at 11:53:39AM +0100, Ingo Molnar wrote:
> > > + do_trap(trapnr, signr, str, regs, error_code, BUS_ADRALN, NULL);
> > > + }
> > > +}
> >
> > Is there any experience with how frequently this signal is killing
> > user-space processes on a modern distro? Any expectation of how frequent
> > such SIGBUS task terminations are going to be in the field?
> We did pretty intensive testing internally (zero day tests, many engineers
> and testers use the patches in their dailly work, etc). So far I'm not
> aware of any user space process hiting split lock issue. I guess GCC or
> other compilers takes care of the issue already. Inline assembly code may
> hit the issue if code is not right, but there are fewer inline assembly
> code in user space.
> So far we only find two kernel split lock issues and fix them in the first
> two patches in this patch set. We also find one BIOS split lock issue
> internally which has been fixed in production BIOS.
> Thanks.

Ok, still, for binary compatibility's sake, could you please add a sysctl
knob (root-only, etc.) and a kernel boot parameter that disables this

Looks good otherwise.