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AJvYcCUJZnCi8LRatE9YTV26bOW9fh54ghLLF6vhUNGL4MTpCHe7jhDe8hK8V1vsDRnFIyxIZS7mQJp/Xw==@kvack.org X-Gm-Message-State: AOJu0YyGSzc3SbgbZSy+LLE3rUWCukt6blrHt/k+bHsZmy1OnXVfgo3U TlMAn720kYizDr+7+gmCQ7GoTO5uXYmQYvoXyCKPB9Z/Jauq/DELjD3U1ax9/lICnpL+u9EVxfi gbkOFf5i7Ijx/IOOKyUB/EvOLNtyD2A3pR91x9w== X-Gm-Gg: ASbGnctMN+cr8XQr9NRmTE93hCYQY2ByUAVYim/ZFQuf0U/ZRPc48Mi1Bm1dPoNjwYE aPwrG5jqnxigyOS80+hxt7lU0YAGopXVif7+p X-Google-Smtp-Source: AGHT+IERxfeFHnzWGjnXWaunMgWNYVqkpPBsLMjAfHFuRIKYyNJQAYs2iiNndqzYqxmZbY3OMdZCdjicGUrYBZW+yZ8= X-Received: by 2002:a05:6512:1053:b0:53e:bedb:867f with SMTP id 2adb3069b0e04-540905aacbfmr97792e87.41.1734049630826; Thu, 12 Dec 2024 16:27:10 -0800 (PST) MIME-Version: 1.0 References: <20241210160556.2341497-1-arnd@kernel.org> <20241210160556.2341497-3-arnd@kernel.org> <20241211152257.Igx3aT2Y@linutronix.de> In-Reply-To: <20241211152257.Igx3aT2Y@linutronix.de> From: Linus Walleij Date: Fri, 13 Dec 2024 01:27:00 +0100 Message-ID: Subject: Re: [PATCH 2/4] ARM: Disable HIGHPTE on PREEMPT_RT kernels To: Sebastian Andrzej Siewior Cc: Arnd Bergmann , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Arnd Bergmann , linux-mm@kvack.org, linux-rt-devel@lists.linux.dev, Ard Biesheuvel , Clark Williams , Jason Baron , Josh Poimboeuf , Mark Rutland , Matthew Wilcox , Peter Zijlstra , Russell King , Steven Rostedt , David Hildenbrand Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 83FDE2000F X-Rspam-User: X-Stat-Signature: 83ojkiawmanaqhkph7negew3pdykfq3n X-HE-Tag: 1734049621-899209 X-HE-Meta: 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 rST3Gqte DaYplG31AY/UB/qKP0V+zdbMhaUU8qmLLX2Eg/pHya8qbiOmdjnS4DAXY1TNN0I73b5divkUZidpm6qLkaHAxKJ3QrtkMqkjtZtlkjqwJp4lODqmZooGtuFZARu21KPUyd6NpHhTuo2iCzbjBrgaahqQgeKShEEKPtpUWYi/9wQ9sPJnktFw2y89aX8zo3EXauZYDBQzpTMsHTQff4VfHome2gHVY4A8qcSja97lXB+ryLOM= X-Bogosity: Ham, tests=bogofilter, spamicity=0.118786, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Dec 11, 2024 at 4:22=E2=80=AFPM Sebastian Andrzej Siewior 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? > =E2=80=A6 > > 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 viol= ating > > 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