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From: David Laight <David.Laight@ACULAB.COM>
To: 'Mathieu Desnoyers' <mathieu.desnoyers@efficios.com>
Cc: Christian Brauner <christian.brauner@ubuntu.com>,
	Christian Brauner <brauner@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	paulmck <paulmck@kernel.org>, Boqun Feng <boqun.feng@gmail.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Paul Turner <pjt@google.com>,
	linux-api <linux-api@vger.kernel.org>,
	Florian Weimer <fw@deneb.enyo.de>, carlos <carlos@redhat.com>
Subject: RE: [RFC PATCH v2 1/2] rseq: x86: implement abort-at-ip extension
Date: Wed, 12 Jan 2022 15:15:27 +0000	[thread overview]
Message-ID: <0088806280f54211b3f90b2c1a82a140@AcuMS.aculab.com> (raw)
In-Reply-To: <1953851780.24610.1641999934047.JavaMail.zimbra@efficios.com>

From: Mathieu Desnoyers
> Sent: 12 January 2022 15:06
> 
> ----- On Jan 12, 2022, at 9:58 AM, David Laight David.Laight@ACULAB.COM wrote:
> 
> >>  * [*] The openrisc, powerpc64 and x86-64 architectures define a "redzone" as a
> >>  *     stack area beyond the stack pointer which can be used by the compiler
> >>  *     to store local variables in leaf functions.
> >
> > I wonder if that is really worth the trouble it causes!
> > By the time a function is spilling values to stack the cost
> > of a %sp update is almost certainly noise.
> >
> > Someone clearly thought it was a 'good idea (tm)'.
> 
> I must admit that I've been surprised to learn about these redzones. Thanks for
> pointing them out to me, it was clearly a blind spot. I suspect it would be useful
> to introduce per-architecture KERNEL_REDZONE, USER_REDZONE and COMPAT_USER_REDZONE
> with a asm-generic version defining them to 0, with proper documentation. It would
> make it clearer to kernel developers working on stuff similar to signal handler
> delivery that they need to consider these carefully.

They can never be used in kernel - any ISR would overwrite them.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

  reply	other threads:[~2022-01-12 15:15 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-10 17:16 [RFC PATCH v2 1/2] rseq: x86: implement abort-at-ip extension Mathieu Desnoyers
2022-01-10 17:16 ` [RFC PATCH v2 2/2] selftests: rseq: test abort-at-ip extension on x86 Mathieu Desnoyers
2022-01-11  5:31 ` [RFC PATCH v2 1/2] rseq: x86: implement abort-at-ip extension kernel test robot
2022-01-11 11:05 ` Christian Brauner
2022-01-11 17:43   ` Mathieu Desnoyers
2022-01-12  8:46     ` Christian Brauner
2022-01-12 14:47       ` Mathieu Desnoyers
2022-01-12 14:55         ` Christian Brauner
2022-01-12 14:58         ` David Laight
2022-01-12 15:05           ` Mathieu Desnoyers
2022-01-12 15:15             ` David Laight [this message]
2022-01-12 15:24               ` Mathieu Desnoyers
2022-01-12 15:34               ` Peter Zijlstra
2022-01-12 15:53                 ` David Laight
2022-01-12 19:03 ` kernel test robot
2022-01-12 19:03   ` kernel test robot

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