On Thu, Feb 01, 2018 at 12:22:40PM -0500, Vince Weaver wrote:

On Thu, 1 Feb 2018, Linus Torvalds wrote:

quoted

On Thu, Feb 1, 2018 at 6:18 AM, Vince Weaver [off-list ref] wrote:

quoted

I thought that to get into stable the patch had to be in upstream first.

Upstream does have the fix, it's just very very different in this case.

The upstream fix is commit 99a9dc98ba52 ("x86,perf: Disable intel_bts
when PTI"), which just disables intel_bts entirely, because upstream
doesn't do those "kaiser_add/remove_mapping()" things.

So this "backport" is ok.

           Linus

Unless I'm misunderstanding, the fix going into 4.4 actually fixes the 
issue (BTS trying to access a VM buffer that is unmapped) using the KAISER 
infrastructure.

The "fix" in 4.15 just disables BTS totally (until someone figures out how 
to fix things properly).

We could produce a better fix, I was kind of waiting to see if anyone
actually cares about intel_bts, especially since one can still get BTS
the "old way" where the data is processed on the kernel side. And most
CPUs these days should have at least some form of PT.

Regards,
--
Alex