From: Peter Zijlstra <peterz@infradead.org>
To: hpa@zytor.com
Cc: Denys Vlasenko <dvlasenk@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Julien Thierry <julien.thierry@arm.com>,
Will Deacon <will.deacon@arm.com>,
Andy Lutomirski <luto@amacapital.net>,
Ingo Molnar <mingo@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
James Morse <james.morse@arm.com>,
valentin.schneider@arm.com, Brian Gerst <brgerst@gmail.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Andrew Lutomirski <luto@kernel.org>,
Borislav Petkov <bp@alien8.de>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
Dmitry Vyukov <dvyukov@google.com>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 01/25] x86: Make SMAP 64-bit only
Date: Thu, 21 Mar 2019 22:03:50 +0100 [thread overview]
Message-ID: <20190321210350.GF2490@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <33D32634-51DC-426D-BE4A-F78B862760D5@zytor.com>
On Thu, Mar 21, 2019 at 11:18:05AM -0700, hpa@zytor.com wrote:
> On March 21, 2019 10:25:05 AM PDT, Denys Vlasenko <dvlasenk@redhat.com> wrote:
> >I did not see evidence of this. In my testing,
> >POPF is always ~20 cycles, even if popped flags are identical to
> >current state of flags.
>
> I think you will find that if you change system flags it is much slower.
So with all the patches in this series applied, only x86_32 will suffer
this, and I don't think anybody still considers that a performance
critical platform.
That said, we could do something terrible like:
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -673,7 +673,8 @@ ENTRY(__switch_to_asm)
#endif
/* restore callee-saved registers */
- popfl
+ ALTERNATIVE "popl %esi", \
+ "popfl", X86_FEATURE_SMAP
popl %esi
popl %edi
popl %ebx
And then you only pay the POPF penalty when you run a 32bit kernel on a
SMAP enabled CPU, and we have a very good solution in that code: run a
64bit kernel.
next prev parent reply other threads:[~2019-03-21 21:04 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-18 15:38 [PATCH 00/25] objtool: UACCESS validation v4 Peter Zijlstra
2019-03-18 15:38 ` [PATCH 01/25] x86: Make SMAP 64-bit only Peter Zijlstra
2019-03-18 16:58 ` Linus Torvalds
2019-03-18 17:36 ` Peter Zijlstra
2019-03-18 17:51 ` Peter Zijlstra
2019-03-18 18:10 ` Linus Torvalds
2019-03-21 17:12 ` hpa
2019-03-21 17:25 ` Denys Vlasenko
2019-03-21 18:18 ` hpa
2019-03-21 21:03 ` Peter Zijlstra [this message]
2019-03-21 18:21 ` Linus Torvalds
2019-03-19 11:16 ` [PATCH 01/25] sched/x86: Save [ER]FLAGS on context switch Peter Zijlstra
2019-03-18 15:38 ` [PATCH 02/25] tracing: Improve "if" macro code generation Peter Zijlstra
2019-03-18 17:41 ` Steven Rostedt
2019-03-18 23:37 ` Josh Poimboeuf
2019-03-19 10:11 ` Peter Zijlstra
2019-03-20 11:18 ` David Laight
2019-03-20 17:26 ` Linus Torvalds
2019-03-20 17:37 ` David Laight
2019-03-20 17:38 ` Linus Torvalds
2019-03-20 18:18 ` Steven Rostedt
2019-05-09 13:00 ` Steven Rostedt
2019-05-09 16:51 ` Linus Torvalds
2019-05-09 18:29 ` Steven Rostedt
2019-05-09 18:45 ` Josh Poimboeuf
2019-05-09 18:47 ` Josh Poimboeuf
2019-05-09 18:48 ` Randy Dunlap
2019-05-09 18:57 ` Josh Poimboeuf
2019-05-09 19:06 ` Steven Rostedt
2019-05-09 19:28 ` Steven Rostedt
2019-05-09 19:44 ` Linus Torvalds
2019-03-18 15:38 ` [PATCH 03/25] x86/ia32: Fix ia32_restore_sigcontext AC leak Peter Zijlstra
2019-03-18 15:38 ` [PATCH 04/25] i915,uaccess: Fix redundant CLAC Peter Zijlstra
2019-03-18 15:38 ` [PATCH 05/25] x86/uaccess: Move copy_user_handle_tail into asm Peter Zijlstra
2019-03-18 15:38 ` [PATCH 06/25] x86/uaccess: Fix up the fixup Peter Zijlstra
2019-03-18 15:38 ` [PATCH 07/25] x86/nospec,objtool: Introduce ANNOTATE_IGNORE_ALTERNATIVE Peter Zijlstra
2019-03-18 15:38 ` [PATCH 08/25] x86/uaccess,xen: Suppress SMAP warnings Peter Zijlstra
2019-03-18 15:38 ` [PATCH 09/25] x86/uaccess: Always inline user_access_begin() Peter Zijlstra
2019-03-18 15:38 ` [PATCH 10/25] x86/uaccess,signal: Fix AC=1 bloat Peter Zijlstra
2019-03-18 15:38 ` [PATCH 11/25] x86/uaccess: Introduce user_access_{save,restore}() Peter Zijlstra
2019-03-18 15:38 ` [PATCH 12/25] x86/smap: Ditch __stringify() Peter Zijlstra
2019-03-18 15:38 ` [PATCH 13/25] x86/uaccess,kasan: Fix KASAN vs SMAP Peter Zijlstra
2019-03-18 15:38 ` [PATCH 14/25] x86/uaccess,ubsan: Fix UBSAN " Peter Zijlstra
2019-03-18 15:38 ` [PATCH 15/25] x86/uaccess,ftrace: Fix ftrace_likely_update() " Peter Zijlstra
2019-03-18 15:38 ` [PATCH 16/25] x86/uaccess,kcov: Disable stack protector Peter Zijlstra
2019-03-18 15:38 ` [PATCH 17/25] objtool: Set insn->func for alternatives Peter Zijlstra
2019-03-18 15:38 ` [PATCH 18/25] objtool: Handle function aliases Peter Zijlstra
2019-03-18 15:38 ` [PATCH 19/25] objtool: Rewrite add_ignores() Peter Zijlstra
2019-03-18 15:39 ` [PATCH 20/25] objtool: Add --backtrace support Peter Zijlstra
2019-03-18 15:39 ` [PATCH 21/25] objtool: Rewrite alt->skip_orig Peter Zijlstra
2019-03-18 15:39 ` [PATCH 22/25] objtool: Fix sibling call detection Peter Zijlstra
2019-03-18 15:39 ` [PATCH 23/25] objtool: Add UACCESS validation Peter Zijlstra
2019-03-18 23:51 ` Josh Poimboeuf
2019-05-07 11:52 ` Peter Zijlstra
2019-03-18 15:39 ` [PATCH 24/25] objtool: uaccess PUSHF/POPF support Peter Zijlstra
2019-03-18 15:39 ` [PATCH 25/25] objtool: Add Direction Flag validation Peter Zijlstra
2019-03-18 23:57 ` [PATCH 00/25] objtool: UACCESS validation v4 Josh Poimboeuf
2019-03-19 11:20 ` Peter Zijlstra
2019-03-19 11:17 ` [PATCH 26/25] sched/x86_64: Don't save flags on context switch Peter Zijlstra
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190321210350.GF2490@worktop.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=bp@alien8.de \
--cc=brgerst@gmail.com \
--cc=catalin.marinas@arm.com \
--cc=dvlasenk@redhat.com \
--cc=dvyukov@google.com \
--cc=hpa@zytor.com \
--cc=james.morse@arm.com \
--cc=jpoimboe@redhat.com \
--cc=julien.thierry@arm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@amacapital.net \
--cc=luto@kernel.org \
--cc=mingo@kernel.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
--cc=valentin.schneider@arm.com \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox
Powered by JetHome