linux-kernel - Re: [RFC][PATCH] tracing/x86: Save CR2 before tracing irqsoff on error

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Message-ID: <CAHk-=wjEHqY1+DxJ-_oNWTuTNQwMPtJKJh_HE=e1F60V+TwUfQ@mail.gmail.com>
Date:   Thu, 21 Mar 2019 11:25:44 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Andrew Cooper <andrew.cooper3@...rix.com>,
        Jan Beulich <jbeulich@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Joel Fernandes <joel@...lfernandes.org>,
        He Zhe <zhe.he@...driver.com>
Subject: Re: [RFC][PATCH] tracing/x86: Save CR2 before tracing irqsoff on error_entry

On Thu, Mar 21, 2019 at 11:21 AM Andy Lutomirski <luto@...nel.org> wrote:
>
> I dunno.  Lots of people at least use to have serious commercial interest in it.

Yes, it used to be a big deal. But full virtualization has gotten a
lot more common and better.

> Hey Xen folks, how close are we to being able to say "if you want to
> run a new kernel, you need to switch to PVH or similar"?

I'd also like to know if we could perhaps at least limit PV to just
the thing that people care most deeply about.

For example, maybe people notice that they really deeply care about
the PV spinlocks because they help a lot for some loads, but don't
care so much about the low-level CPU PV stuff any more because modern
CPUs do _those_ things so well these days.

So it might not be an all-or-nothing thing, but a gradual "let's stop
supporting xyz under PV, because it causes pain and isn't worth it".

                Linus