On Thu, 1 Feb 2018, Linus Torvalds wrote:
On Thu, Feb 1, 2018 at 6:18 AM, Vince Weaver vincent.weaver@maine.edu wrote:
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).
So while in theory both are equivelant fixes ("the kernel no longer crashes when using perf/bts") the mechanism is completely different.
I'm only minorly complaining because I do a lot of testing/fuzzing on linux-git to catch perf related issues (I'm the one who first reported this issue in the first place). But I typically don't test the stable trees, and now we more or less have a fork where the perf/bts code is doing something very different in stable vs head.
Vince