Re: [RFC][PATCH] tracing/x86: Save CR2 before tracing irqsoff on error_entry

[Peter Zijlstra]

On Thu, Mar 21, 2019 at 11:05:06AM -0700, Andy Lutomirski wrote:

> Ugh.
> 
> I certainly agree in principle that sticking the CR2 read into the asm
> is the right solution.  But this patch makes the spaghetti even more
> tangled.  Maybe we can rearrange the code a bit so that the entry
> sequence saves at least one register before calling error_entry, so we
> can do it the obvious way.

What is the obvious way? Note that with all the Xen/paravirt-me-harder
bits on, we need to clobber at least RAX to get CR2.

And most of the patch was munging the paravirt bits to make that happen.

Another thing I did notices is that CLAC and CLD are not next to one
another in these paths.