Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220902130625.217071627@infradead.org> <20220902130950.205726504@infradead.org>
 <CAHk-=wig7_=CpkvZXrbcM97pBGk5MCbVkA0yBGP2moiho-XS_Q@mail.gmail.com>
 <YxI3Zf5drSHAkBL3@hirez.programming.kicks-ass.net> <YxJmdG9Ug7euJdZS@hirez.programming.kicks-ass.net>
 <CAHk-=wj-njE+DwycFcVQ=ouXZpgKU2rjG3G0keNXSFWa_etrEA@mail.gmail.com>
In-Reply-To: <CAHk-=wj-njE+DwycFcVQ=ouXZpgKU2rjG3G0keNXSFWa_etrEA@mail.gmail.com>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sat, 3 Sep 2022 10:26:45 -0700
Message-ID: <CAHk-=whbunYr933WanyFxjp_WkT-NWNtSE6pt5A9Jq9_DjymEw@mail.gmail.com>
Subject: Re: [PATCH v2 37/59] x86/putuser: Provide room for padding
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
        x86@kernel.org, Tim Chen <tim.c.chen@linux.intel.com>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Andrew Cooper <Andrew.Cooper3@citrix.com>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Johannes Wikner <kwikner@ethz.ch>,
        Alyssa Milburn <alyssa.milburn@linux.intel.com>,
        Jann Horn <jannh@google.com>, "H.J. Lu" <hjl.tools@gmail.com>,
        Joao Moreira <joao.moreira@intel.com>,
        Joseph Nuzman <joseph.nuzman@intel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Juergen Gross <jgross@suse.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        K Prateek Nayak <kprateek.nayak@amd.com>,
        Eric Dumazet <edumazet@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Sep 2, 2022 at 2:46 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Hmm. It doesn't look too horrible, but yeah, fi it still ends up
> getting the same padding overhead I'm not sure it ends up really
> mattering.

Oh, and I think it's buggy anyway.

If there are any tail-calls to a leaf function, the tracking now gets
out of whack. So it's no longer a "don't bother counting the last
level", now it ends up being a "count got off by one".

Oh well.

             Linus