From: Linus Walleij <linus.walleij@linaro.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Arnd Bergmann <arnd@kernel.org>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
linux-mm@kvack.org, linux-rt-devel@lists.linux.dev,
Ard Biesheuvel <ardb@kernel.org>,
Clark Williams <clrkwllms@kernel.org>,
Jason Baron <jbaron@akamai.com>,
Josh Poimboeuf <jpoimboe@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Matthew Wilcox <willy@infradead.org>,
Peter Zijlstra <peterz@infradead.org>,
Russell King <linux@armlinux.org.uk>,
Steven Rostedt <rostedt@goodmis.org>,
David Hildenbrand <david@redhat.com>
Subject: Re: [PATCH 2/4] ARM: Disable HIGHPTE on PREEMPT_RT kernels
Date: Fri, 13 Dec 2024 01:27:00 +0100 [thread overview]
Message-ID: <CACRpkdbYU=Txm0zUWDWvNXA0JHRNGpy1ccy0zQdiBb2Ya+UBFA@mail.gmail.com> (raw)
In-Reply-To: <20241211152257.Igx3aT2Y@linutronix.de>
On Wed, Dec 11, 2024 at 4:22 PM Sebastian Andrzej Siewior
<bigeasy@linutronix.de> wrote:
> On 2024-12-11 14:29:29 [+0100], Linus Walleij wrote:
> > So fast GUP is supposed to be lockless, and should just not
> > have this problem. So it can't be addressing gup_fast_pgd_range()
> > right?
> …
> > I'm more asking if HIGHPTE even acquires a spinlock anymore
> > as it is supposed to be "fast"/lockless. If it does, it is clearly violating
> > the "fast" promise of the fast GUP API and should not exist.
>
> This is lockless on x86. The problem is ARM's
> arch_kmap_local_high_get(). This is where the lock is from.
Aha that calls down to kmap_high_get() that that issues
lock_kmap_any(flags).
But is it really sound that the "fast" API does this? It feels
like a violation of the whole design of the fast stuff.
Yours,
Linus Walleij
next prev parent reply other threads:[~2024-12-13 0:27 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-12-10 16:05 [PATCH 0/4] ARM: towards 32-bit preempt-rt support Arnd Bergmann
2024-12-10 16:05 ` [PATCH 1/4] ARM: Disable jump-label on PREEMPT_RT Arnd Bergmann
2024-12-11 13:04 ` Linus Walleij
2024-12-11 13:26 ` Sebastian Andrzej Siewior
2024-12-10 16:05 ` [PATCH 2/4] ARM: Disable HIGHPTE on PREEMPT_RT kernels Arnd Bergmann
2024-12-11 13:29 ` Linus Walleij
2024-12-11 15:22 ` Sebastian Andrzej Siewior
2024-12-13 0:27 ` Linus Walleij [this message]
2024-12-13 9:11 ` Russell King (Oracle)
2024-12-14 22:11 ` Matthew Wilcox
2024-12-11 13:48 ` Sebastian Andrzej Siewior
2024-12-11 14:04 ` Sebastian Andrzej Siewior
2024-12-11 14:30 ` Arnd Bergmann
2024-12-11 15:55 ` Russell King (Oracle)
2024-12-20 14:37 ` Arnd Bergmann
2024-12-10 16:05 ` [PATCH 3/4] ARM: drop CONFIG_HIGHPTE support Arnd Bergmann
2024-12-11 13:32 ` Linus Walleij
2024-12-11 13:50 ` Russell King (Oracle)
2024-12-11 14:31 ` Linus Walleij
2024-12-11 14:25 ` Sebastian Andrzej Siewior
2024-12-14 18:40 ` David Laight
2024-12-20 13:10 ` Linus Walleij
2024-12-20 14:30 ` Arnd Bergmann
2024-12-10 16:05 ` [PATCH 4/4] mm: drop HIGHPTE support altogether Arnd Bergmann
2024-12-11 13:53 ` Linus Walleij
2024-12-11 14:29 ` Sebastian Andrzej Siewior
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