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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1781800852; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=xeiijMLpLKaaOkBdp35eM6zjfD+uzItWtXaFrZwEr/A=; b=YRN/MCBgQjjjy+x0E2HVms6+4UopRfdKkRjbBBd6raI83Ir4b0lNXN6gwHsucVI50zBlsY ui/ezbdRaiIBRz5V6y5LEvG4vT8e2PVUVtQtOUToeND8UuUp6XHPPBr3J1Zvy0p3QgLzJM w4Ep695ahAYnUkrvERLu5oC9iUgO3Gc= From: Usama Arif To: Rik van Riel Cc: Usama Arif , linux-kernel@vger.kernel.org, x86@kernel.org, linux-mm@kvack.org, "Thomas Gleixner" , "Ingo Molnar" , "Dmitry Ilvokhin" , "Borislav Petkov" , "Dave Hansen" , "Andrew Morton" , "David Hildenbrand" , "Lorenzo Stoakes" , "Liam R. Howlett" , "Vlastimil Babka" , "Suren Baghdasaryan" Subject: Re: [PATCH 1/3] x86/mm: use READ_ONCE/WRITE_ONCE for mm->context.untag_mask Date: Thu, 18 Jun 2026 09:40:42 -0700 Message-ID: <20260618164043.784764-1-usama.arif@linux.dev> In-Reply-To: <20260616190300.1509639-2-riel@surriel.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 0EE07A0005 X-Rspam-User: X-Stat-Signature: 6e9pqm1pccr4a4qif1gzhzykjrrts1ck X-HE-Tag: 1781800854-205940 X-HE-Meta: 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 NJeWuV8x 5yvr4WdxAK1kAozqq19bUrkWD8ULmpjva5Yplvu5kiRQPPDgQ41NbpAmEfp6XhYyaC5WbVGpfFhf8wxBPg39+OsR+TuRCQ7tyMaG36ZwT0M6/aM11IwIFUOg1lnGUatW56GdH0RkjRGWv5pInvRGd4O8G6aXoY1hf01D/f8siCVVj+ubeu+xM8ronraLG1jzdV/QQzFXAdY0aQ+Sj3+btW5AT8GVqRbPibvV9uf8WaLp33ytbPXVG158IZOYytepwoJZAzW1li8RnmEiA6yRXrNDR5VDykRSjy4UM+o3KcRn7l2XikWZUUgpWBQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 16 Jun 2026 15:02:58 -0400 Rik van Riel wrote: > mm->context.untag_mask is written once, when LAM is enabled > (mm_enable_lam(), under mmap_write_lock and while the process is still > single-threaded), and is otherwise stable and never reverted. > untagged_addr_remote() reads it for a remote mm, and the new > untagged_addr_remote_unlocked() (used by the per-VMA-lock > access_remote_vm() fast path) reads it without the mmap lock. > > The field is a single aligned word and cannot tear, but annotate the > reads and writes with READ_ONCE()/WRITE_ONCE() to make the lockless > access explicit and keep the compiler from reloading or tearing it. > > No functional change. > > Assisted-by: Claude:claude-opus-4-8 > Signed-off-by: Rik van Riel > --- > arch/x86/include/asm/mmu_context.h | 6 +++--- > arch/x86/include/asm/uaccess_64.h | 2 +- > arch/x86/kernel/process_64.c | 2 +- > 3 files changed, 5 insertions(+), 5 deletions(-) > Acked-by: Usama Arif