From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 82E7618A6B8 for ; Wed, 11 Dec 2024 15:23:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733930582; cv=none; b=IThofJiKB9DzqXh99M7CbnzH/QscnRbQYMcQebiXJHg89tGJIM/4+p4jht8sdTmfmXcrKikwX5N5ZB9fBi7oOJV/sTbe/5YusczNhaJm3dYoKddR1TUt0Gy812DMGXB07qE1iIBm3v+grJTPx65OcnZMihv54DMZBp/jIZMfoD8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733930582; c=relaxed/simple; bh=Bj3HLfAaTEgLybrOE17CqojJW6/IovPwqNCEJh+a3x8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ju4qIyIvnxQqGdYywRZXa0gbE7wshUUYHBo3mKDvqs8daTFj1yYTXjCPPJ1ZDFABUiBq+sEUPqvYG6p8oVGnzfI+lfQbf6ouOzYg5zuOSBlIzXxnGtC9Z//HNr0xXm69cu8n+GcEC3qw7UeVlyIn/X+OHtoAkVyMmL3RSkbpz6o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=jPnbSjYA; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=2CAw6C3I; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="jPnbSjYA"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="2CAw6C3I" Date: Wed, 11 Dec 2024 16:22:57 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1733930578; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Bj3HLfAaTEgLybrOE17CqojJW6/IovPwqNCEJh+a3x8=; b=jPnbSjYAsa/3sIBGYkpSL+Hfi0cotmj+NqQRjX4DYUGn8NA2Dv7MggsijYQ99IwrFB74T+ K8xRV5yft1JGhjyBEH3ObAy0L4yqTDuCFEMoNcVa76sj1lRTOK/iFuiL7gASoGENOwzdTV hwOwiZLw1sP4f3iWyIx/91rA0DRySeA7gdLeYSCkM+nlBHlAXltDBaA73jP6DdV406N2Xk 1+4CQwja+N77cYhux6O95ozJxvA1wARSq+kGfBF0LVPsk0RhoCZvCfTvHvMSL8Y8+fUUDw INuFoRhQeiJY4KK9u9xEWaq6Of5d+cljh99nfxZVkc0NPwJUsSNTnq7AqKARXQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1733930578; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Bj3HLfAaTEgLybrOE17CqojJW6/IovPwqNCEJh+a3x8=; b=2CAw6C3I9ByddGJoOgM225O/zgyu2W/7Ypk8MHxeGq8x/Shuiv2hVVY7QAANWiEVmyaF1u VXD6kQ4mJJ1TNfDQ== From: Sebastian Andrzej Siewior To: Linus Walleij 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 Subject: Re: [PATCH 2/4] ARM: Disable HIGHPTE on PREEMPT_RT kernels Message-ID: <20241211152257.Igx3aT2Y@linutronix.de> References: <20241210160556.2341497-1-arnd@kernel.org> <20241210160556.2341497-3-arnd@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: 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 violat= ing > 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. > Yours, > Linus Walleij Sebastian