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From: Al Viro <viro@zeniv.linux.org.uk>
To: Doug Anderson <dianders@chromium.org>
Cc: Christian Brauner <brauner@kernel.org>,
	Eric Biederman <ebiederm@xmission.com>, Jan Kara <jack@suse.cz>,
	Kees Cook <keescook@chromium.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, Oleg Nesterov <oleg@redhat.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] regset: use vmalloc() for regset_get_alloc()
Date: Fri, 2 Feb 2024 16:55:24 +0000	[thread overview]
Message-ID: <20240202165524.GD2087318@ZenIV> (raw)
In-Reply-To: <20240202164947.GC2087318@ZenIV>

On Fri, Feb 02, 2024 at 04:49:47PM +0000, Al Viro wrote:
> > +folks from `./scripts/get_maintainer.pl -f arch/arm64/kernel/ptrace.c`
> > 
> > Trying to follow the macros to see where "n" comes from is a maze of
> > twisty little passages, all alike. Hopefully someone from the ARM
> > world can help tell if the value of 17474 for n here is correct or if
> > something is wonky.
> 
> It might be interesting to have it print the return value of __regset_get()
> in those cases; if *that* is huge, we really have a problem.  If it ends up
> small enough to fit into few pages, OTOH...
> 
> SVE_VQ_MAX is defined as 255; is that really in units of 128 bits?  IOW,
> do we really expect to support 32Kbit registers?  That would drive the
> size into that range, all right, but it would really suck on context
> switches.
> 
> I could be misreading it, though - the macros in there are not easy to
> follow and I've never dealt with SVE before, so take the above with
> a cartload of salt.

Worse - it's SVE_VQ_MAX is 512; sorry about the confusion.  OK, that would
certainly explain the size (header + 32 registers, each up to 512 * 16 bytes),
but... ouch.

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WARNING: multiple messages have this Message-ID (diff)
From: Al Viro <viro@zeniv.linux.org.uk>
To: Doug Anderson <dianders@chromium.org>
Cc: Christian Brauner <brauner@kernel.org>,
	Eric Biederman <ebiederm@xmission.com>, Jan Kara <jack@suse.cz>,
	Kees Cook <keescook@chromium.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, Oleg Nesterov <oleg@redhat.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] regset: use vmalloc() for regset_get_alloc()
Date: Fri, 2 Feb 2024 16:55:24 +0000	[thread overview]
Message-ID: <20240202165524.GD2087318@ZenIV> (raw)
In-Reply-To: <20240202164947.GC2087318@ZenIV>

On Fri, Feb 02, 2024 at 04:49:47PM +0000, Al Viro wrote:
> > +folks from `./scripts/get_maintainer.pl -f arch/arm64/kernel/ptrace.c`
> > 
> > Trying to follow the macros to see where "n" comes from is a maze of
> > twisty little passages, all alike. Hopefully someone from the ARM
> > world can help tell if the value of 17474 for n here is correct or if
> > something is wonky.
> 
> It might be interesting to have it print the return value of __regset_get()
> in those cases; if *that* is huge, we really have a problem.  If it ends up
> small enough to fit into few pages, OTOH...
> 
> SVE_VQ_MAX is defined as 255; is that really in units of 128 bits?  IOW,
> do we really expect to support 32Kbit registers?  That would drive the
> size into that range, all right, but it would really suck on context
> switches.
> 
> I could be misreading it, though - the macros in there are not easy to
> follow and I've never dealt with SVE before, so take the above with
> a cartload of salt.

Worse - it's SVE_VQ_MAX is 512; sorry about the confusion.  OK, that would
certainly explain the size (header + 32 registers, each up to 512 * 16 bytes),
but... ouch.

  reply	other threads:[~2024-02-02 16:56 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-02-02  1:12 [PATCH] regset: use vmalloc() for regset_get_alloc() Douglas Anderson
2024-02-02  1:22 ` Al Viro
2024-02-02  2:54   ` Doug Anderson
2024-02-02  3:04     ` Al Viro
2024-02-02  3:15       ` Doug Anderson
2024-02-02  3:49         ` Al Viro
2024-02-02  4:05           ` Al Viro
2024-02-02 16:24             ` Doug Anderson
2024-02-02 16:24               ` Doug Anderson
2024-02-02 16:49               ` Al Viro
2024-02-02 16:49                 ` Al Viro
2024-02-02 16:55                 ` Al Viro [this message]
2024-02-02 16:55                   ` Al Viro
2024-02-02 18:07                   ` Dave Martin
2024-02-02 18:07                     ` Dave Martin
2024-02-02 19:13                     ` Doug Anderson
2024-02-02 19:13                       ` Doug Anderson
2024-02-02 19:42                     ` Mark Brown
2024-02-02 19:42                       ` Mark Brown
2024-02-02 20:38                       ` Doug Anderson
2024-02-02 20:38                         ` Doug Anderson
2024-02-02 17:48           ` Mark Brown
2024-02-02  1:24 ` Matthew Wilcox
2024-02-02  2:58   ` Doug Anderson

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