From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.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>
Subject: Re: [PATCH v2 37/59] x86/putuser: Provide room for padding
Date: Fri, 2 Sep 2022 19:03:33 +0200 [thread overview]
Message-ID: <YxI3Zf5drSHAkBL3@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAHk-=wig7_=CpkvZXrbcM97pBGk5MCbVkA0yBGP2moiho-XS_Q@mail.gmail.com>
On Fri, Sep 02, 2022 at 09:43:45AM -0700, Linus Torvalds wrote:
> So I don't hate this patch and it's probably good for consistency, but
> I really think that the retbleed tracking could perhaps be improved to
> let this be all unnecessary.
>
> The whole return stack depth counting is already not 100% exact, and I
> think we could just make the rule be that we don't track leaf
> functions.
>
> Why? It's just a off-by-one in the already not exact tracking. And -
> perhaps equally importantly - leaf functions are very very common
> dynamically, and I suspect it's trivial to see them.
>
> Yes, yes, you could make objtool even smarter and actually do some
> kind of function flow graph thing (and I think some people were
> talking about that with the whole ret counting long long ago), but the
> leaf function thing is the really simple low-hanging fruit case of
> that.
So I did the leaf thing a few weeks ago, and at the time the perf gains
where not worth the complexity.
I can try again :-)
next prev parent reply other threads:[~2022-09-02 17:04 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-02 13:06 [PATCH v2 00/59] x86/retbleed: Call depth tracking mitigation Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 01/59] x86/paravirt: Ensure proper alignment Peter Zijlstra
2022-09-02 16:05 ` Juergen Gross
2022-09-02 13:06 ` [PATCH v2 02/59] x86/cpu: Remove segment load from switch_to_new_gdt() Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 03/59] x86/cpu: Get rid of redundant switch_to_new_gdt() invocations Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 04/59] x86/cpu: Re-enable stackprotector Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 05/59] x86/modules: Set VM_FLUSH_RESET_PERMS in module_alloc() Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 06/59] x86/vdso: Ensure all kernel code is seen by objtool Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 07/59] x86: Sanitize linker script Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 08/59] x86/build: Ensure proper function alignment Peter Zijlstra
2022-09-02 16:51 ` Linus Torvalds
2022-09-02 17:32 ` Peter Zijlstra
2022-09-02 18:08 ` Linus Torvalds
2022-09-05 10:04 ` Peter Zijlstra
2022-09-12 14:09 ` Linus Torvalds
2022-09-12 19:44 ` Peter Zijlstra
2022-09-13 8:08 ` Peter Zijlstra
2022-09-13 13:08 ` Linus Torvalds
2022-09-05 2:09 ` David Laight
2022-09-02 13:06 ` [PATCH v2 09/59] x86/asm: " Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 10/59] x86/error_inject: Align function properly Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 11/59] x86/paravirt: Properly align PV functions Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 12/59] x86/entry: Align SYM_CODE_START() variants Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 13/59] crypto: x86/camellia: Remove redundant alignments Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 14/59] crypto: x86/cast5: " Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 15/59] crypto: x86/crct10dif-pcl: " Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 16/59] crypto: x86/serpent: " Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 17/59] crypto: x86/sha1: Remove custom alignments Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 18/59] crypto: x86/sha256: " Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 19/59] crypto: x86/sm[34]: Remove redundant alignments Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 20/59] crypto: twofish: " Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 21/59] crypto: x86/poly1305: Remove custom function alignment Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 22/59] x86: Put hot per CPU variables into a struct Peter Zijlstra
2022-09-02 18:02 ` Jann Horn
2022-09-15 11:22 ` Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 23/59] x86/percpu: Move preempt_count next to current_task Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 24/59] x86/percpu: Move cpu_number " Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 25/59] x86/percpu: Move current_top_of_stack " Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 26/59] x86/percpu: Move irq_stack variables " Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 27/59] x86/softirq: Move softirq pending next to current task Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 28/59] objtool: Allow !PC relative relocations Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 29/59] objtool: Track init section Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 30/59] objtool: Add .call_sites section Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 31/59] objtool: Add --hacks=skylake Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 32/59] objtool: Allow STT_NOTYPE -> STT_FUNC+0 tail-calls Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 33/59] objtool: Fix find_{symbol,func}_containing() Peter Zijlstra
2022-09-02 13:06 ` [PATCH v2 34/59] objtool: Allow symbol range comparisons for IBT/ENDBR Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 35/59] x86/entry: Make sync_regs() invocation a tail call Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 36/59] ftrace: Add HAVE_DYNAMIC_FTRACE_NO_PATCHABLE Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 37/59] x86/putuser: Provide room for padding Peter Zijlstra
2022-09-02 16:43 ` Linus Torvalds
2022-09-02 17:03 ` Peter Zijlstra [this message]
2022-09-02 20:24 ` Peter Zijlstra
2022-09-02 21:46 ` Linus Torvalds
2022-09-03 17:26 ` Linus Torvalds
2022-09-05 7:16 ` Peter Zijlstra
2022-09-05 11:26 ` Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 38/59] x86/Kconfig: Add CONFIG_CALL_THUNKS Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 39/59] x86/Kconfig: Introduce function padding Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 40/59] x86/retbleed: Add X86_FEATURE_CALL_DEPTH Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 41/59] x86/alternatives: Provide text_poke_copy_locked() Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 42/59] x86/entry: Make some entry symbols global Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 43/59] x86/paravirt: Make struct paravirt_call_site unconditionally available Peter Zijlstra
2022-09-02 16:09 ` Juergen Gross
2022-09-02 13:07 ` [PATCH v2 44/59] x86/callthunks: Add call patching for call depth tracking Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 45/59] x86/modules: Add call patching Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 46/59] x86/returnthunk: Allow different return thunks Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 47/59] x86/asm: Provide ALTERNATIVE_3 Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 48/59] x86/retbleed: Add SKL return thunk Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 49/59] x86/retpoline: Add SKL retthunk retpolines Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 50/59] x86/retbleed: Add SKL call thunk Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 51/59] x86/calldepth: Add ret/call counting for debug Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 52/59] static_call: Add call depth tracking support Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 53/59] kallsyms: Take callthunks into account Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 54/59] x86/orc: Make it callthunk aware Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 55/59] x86/bpf: Emit call depth accounting if required Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 56/59] x86/ftrace: Remove ftrace_epilogue() Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 57/59] x86/ftrace: Rebalance RSB Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 58/59] x86/ftrace: Make it call depth tracking aware Peter Zijlstra
2022-09-02 13:07 ` [PATCH v2 59/59] x86/retbleed: Add call depth tracking mitigation Peter Zijlstra
2022-09-16 9:35 ` [PATCH v2 00/59] x86/retbleed: Call " Mel Gorman
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