All of lore.kernel.org
 help / color / mirror / Atom feed
From: Ard Biesheuvel <ardb@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <frederic@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	James Morse <james.morse@arm.com>,
	Quentin Perret <qperret@google.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Christophe Leroy <christophe.leroy@csgroup.eu>
Subject: Re: [PATCH 2/4] arm64: implement support for static call trampolines
Date: Tue, 21 Sep 2021 16:44:56 +0200	[thread overview]
Message-ID: <CAMj1kXEVjKGkRU_4JWH5d9YzT+pYVuEZYPNLw0VkUAb6d+W9kQ@mail.gmail.com> (raw)
In-Reply-To: <YUmFFvZCb2yXn3os@hirez.programming.kicks-ass.net>

On Tue, 21 Sept 2021 at 09:10, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Tue, Sep 21, 2021 at 01:32:35AM +0200, Frederic Weisbecker wrote:
>
> > +#define __ARCH_DEFINE_STATIC_CALL_TRAMP(name, target)                            \
> > +     asm("   .pushsection    .static_call.text, \"ax\"               \n" \
> > +         "   .align          3                                       \n" \
> > +         "   .globl          " STATIC_CALL_TRAMP_STR(name) "         \n" \
> > +         STATIC_CALL_TRAMP_STR(name) ":                              \n" \
> > +         "   hint    34      /* BTI C */                             \n" \
> > +         "   adrp    x16, 1f                                         \n" \
> > +         "   ldr     x16, [x16, :lo12:1f]                            \n" \
> > +         "   cbz     x16, 0f                                         \n" \
> > +         "   br      x16                                             \n" \
> > +         "0: ret                                                     \n" \
> > +         "   .popsection                                             \n" \
> > +         "   .pushsection    .rodata, \"a\"                          \n" \
> > +         "   .align          3                                       \n" \
> > +         "1: .quad           " target "                              \n" \
> > +         "   .popsection                                             \n")
>
> So I like what Christophe did for PPC32:
>
>   https://lkml.kernel.org/r/6ec2a7865ed6a5ec54ab46d026785bafe1d837ea.1630484892.git.christophe.leroy@csgroup.eu
>
> Where he starts with an unconditional jmp and uses that IFF the offset
> fits and only does the data load when it doesn't. Ard, woulnd't that
> also make sense on ARM64? I'm thinking most in-kernel function pointers
> would actually fit, it's just the module muck that gets to have too
> large pointers, no?
>

Yeah, I'd have to page that back in. But it seems like the following

  bti c
  <branch>
  adrp x16, <literal>
  ldr x16, [x16, ...]
  br x16

with <branch> either set to 'b target' for the near targets, 'ret' for
the NULL target, and 'nop' for the far targets should work, and the
architecture permits patching branches into NOPs and vice versa
without special synchronization. But I must be missing something here,
or why did we have that long discussion before?

  reply	other threads:[~2021-09-21 14:45 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-20 23:32 [PATCH 0/4] arm64: Support dynamic preemption Frederic Weisbecker
2021-09-20 23:32 ` [PATCH 1/4] sched/preempt: Prepare for supporting !CONFIG_GENERIC_ENTRY " Frederic Weisbecker
2021-09-21  7:10   ` Peter Zijlstra
2021-09-21 13:50     ` Mark Rutland
2021-09-20 23:32 ` [PATCH 2/4] arm64: implement support for static call trampolines Frederic Weisbecker
2021-09-21  7:09   ` Peter Zijlstra
2021-09-21 14:44     ` Ard Biesheuvel [this message]
2021-09-21 15:08       ` Peter Zijlstra
2021-09-21 15:33       ` Mark Rutland
2021-09-21 15:55         ` Ard Biesheuvel
2021-09-21 16:28           ` Mark Rutland
2021-09-25 17:46             ` David Laight
2021-09-27  8:58               ` Mark Rutland
2021-09-21 16:10   ` Ard Biesheuvel
2021-09-20 23:32 ` [PATCH 3/4] arm64: Implement IRQ exit preemption static call for dynamic preemption Frederic Weisbecker
2021-09-20 23:32 ` [PATCH 4/4] arm64: Implement HAVE_PREEMPT_DYNAMIC Frederic Weisbecker
2021-10-25 12:20 [PATCH 0/4] arm64: Support dynamic preemption v2 Frederic Weisbecker
2021-10-25 12:21 ` [PATCH 2/4] arm64: implement support for static call trampolines Frederic Weisbecker
2021-10-25 13:56   ` Peter Zijlstra
2021-10-25 14:08     ` Ard Biesheuvel
2021-10-25 14:19       ` Peter Zijlstra
2021-10-25 14:44         ` Peter Zijlstra
2021-10-25 14:55           ` Ard Biesheuvel
2021-10-25 15:03             ` Peter Zijlstra
2021-10-25 15:10               ` Ard Biesheuvel
2021-10-26 10:36                 ` Mark Rutland
2021-10-26 10:45                   ` Peter Zijlstra
2021-10-26 11:06                   ` David Laight
2021-10-27 12:47                     ` Mark Rutland
2021-10-25 15:03             ` David Laight
2021-10-25 14:25   ` David Laight
2021-10-25 14:31     ` Ard Biesheuvel
2021-10-25 14:38       ` David Laight

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=CAMj1kXEVjKGkRU_4JWH5d9YzT+pYVuEZYPNLw0VkUAb6d+W9kQ@mail.gmail.com \
    --to=ardb@kernel.org \
    --cc=catalin.marinas@arm.com \
    --cc=christophe.leroy@csgroup.eu \
    --cc=frederic@kernel.org \
    --cc=james.morse@arm.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mark.rutland@arm.com \
    --cc=peterz@infradead.org \
    --cc=qperret@google.com \
    --cc=will@kernel.org \
    /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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.