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