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From: Peter Zijlstra <peterz@infradead.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	James Morse <james.morse@arm.com>,
	David Laight <David.Laight@aculab.com>,
	Quentin Perret <qperret@google.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>
Subject: Re: [PATCH 2/4] arm64: implement support for static call trampolines
Date: Tue, 26 Oct 2021 12:45:55 +0200	[thread overview]
Message-ID: <YXfcY7PPAvOK9E+8@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20211026103655.GB30152@C02TD0UTHF1T.local>

On Tue, Oct 26, 2021 at 11:36:55AM +0100, Mark Rutland wrote:

> My preference overall is to keep the trampoline self-contained, and I'd
> prefer to keep the RET inline in the trampoline rather than trying to
> factor it out so that all the control-flow is clearly in one place.
> 
> So I'd prefer that we have the sequence as-is:
> 
> | 0:	.quad 0x0
> | 	bti	c
> | 	< insn >
> | 	ldr	x16, 0b
> | 	cbz	x16, 1f
> | 	br	x16
> | 1:	ret

OK, fair enough. In that case:

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Although I do think that function can use a comment to explain the magic
involved.

> If we knew these were only called with IRQs enabled (and so we can take
> an IPI to generate a context synchronization event), we could patch
> <insn> to a RET and point the literal back at the BTI, e.g.

Given the static_call() usage on x86 I'm pretty sure you'll want them
with IRQs disabled.

  reply	other threads:[~2021-10-26 10:46 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-25 12:20 [PATCH 0/4] arm64: Support dynamic preemption v2 Frederic Weisbecker
2021-10-25 12:20 ` [PATCH 1/4] sched/preempt: Prepare for supporting !CONFIG_GENERIC_ENTRY dynamic preemption 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 [this message]
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
2021-10-25 12:21 ` [PATCH 3/4] arm64: Implement IRQ exit preemption static call for dynamic preemption Frederic Weisbecker
2021-10-25 12:21 ` [PATCH 4/4] arm64: Implement HAVE_PREEMPT_DYNAMIC Frederic Weisbecker
  -- strict thread matches above, loose matches on Subject: below --
2021-09-20 23:32 [PATCH 0/4] arm64: Support dynamic preemption Frederic Weisbecker
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
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

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