From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id C6F6A384250 for ; Mon, 18 May 2026 17:21:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779124898; cv=none; b=GIYyL8pfD1aKcetutYD6UhNbv9CEnvNLcyfJ/AirgS87SBwnvqbO3JwxDrE6RkP/u1+jfKeg90UEHrXaZIrmOgb8OwE8IJWg75O+s1wWgrRBS5OS/AY1kOIoFjGZHhz/BXdMI3Rt42UrxeUoq31KVhM0tytvN41GZrotIN7ErQY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779124898; c=relaxed/simple; bh=2Ad+b40QKOgmfGSGo1dsdGk4tJnXSxqznXpiRjuVOyk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=o8jSi3aqktJkUA4EZKO/hFVJSTp6jTj9yX+6bfGXQyKvh74nGDYNXmUBRzfRek3UwrKPwb1vgGeEugJZ8P1g0CMM+1KhYeeqsi/ct6ROkDYqHeyQgmAl4T9rCKCRS2yDHCXRZhM3M8EPgtOlZ8zIEvlyQZB4oI0UnMzedo8bRZ8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=f1G5aw8O; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="f1G5aw8O" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A7B80302D; Mon, 18 May 2026 10:21:30 -0700 (PDT) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 043033F7B4; Mon, 18 May 2026 10:21:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1779124895; bh=2Ad+b40QKOgmfGSGo1dsdGk4tJnXSxqznXpiRjuVOyk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=f1G5aw8O3BbozglFHYWcaZytNBlpNfwL+tPszrn8bRU6NzoZ86pjhSlwh7n6ndYN5 Lz0SSl8gp4UJVzInHX5ZC2Hhm/mHojV7DS2o9ujq5XJC4RtO+7xbn5dvY+JlvLXGnH GmYbu+5CPLnbrnYH8thBVWwZz+kgtyakaQUPSsm4= Date: Mon, 18 May 2026 18:21:26 +0100 From: Catalin Marinas To: Kohei Enju Cc: Will Deacon , Sami Mujawar , Gavin Shan , Steven Price , Suzuki K Poulose , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1] virt: arm-cca-guest: use raw variant of smp_processor_id() in arm_cca_report_new() Message-ID: References: <20260518033157.1865498-1-enju.kohei@fujitsu.com> 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=us-ascii Content-Disposition: inline In-Reply-To: Hi Kohei, On Mon, May 18, 2026 at 10:38:53PM +0900, Kohei Enju wrote: > On 05/18 13:33, Catalin Marinas wrote: > > On Mon, May 18, 2026 at 12:31:31PM +0900, Kohei Enju wrote: > > > diff --git a/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c b/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c > > > index 0c9ea24a200c..2d450caee3e4 100644 > > > --- a/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c > > > +++ b/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c > > > @@ -108,7 +108,7 @@ static int arm_cca_report_new(struct tsm_report *report, void *data) > > > * allocate outblob based on the returned value from the 'init' > > > * call and that cannot be done in an atomic context. > > > */ > > > - cpu = smp_processor_id(); > > > + cpu = raw_smp_processor_id(); > > > > That's just hiding the warning which might be genuine, irrespective of > > what the comment says. Sashiko has some good points: > > > > https://sashiko.dev/#/patchset/20260518033157.1865498-1-enju.kohei@fujitsu.com > > > > Basically what guarantees that the cpu won't go offline? Can we use > > migrate_disable() and ignore the smp_call_function_single() altogether? > > It looks like a hack anyway. [...] > You've raised a very valid point about raw_smp_processor_id() > potentially hiding a genuine issue. I agree this would be a concern in > most contexts. > > However, this implementation was intentionally designed not to block CPU > hotplug: > https://lore.kernel.org/linux-arm-kernel/7a83461d-40fd-4e61-8833-5dae2abaf82b@arm.com/ > > As mentioned in the thread above, the potential failure from the target > CPU going offline (resulting in -ENXIO) is an expected and tolerated > condition in this path. > Using migrate_disable() would go against the non-blocking design goal. > > Given the context, the debug warning looks false positive for our > specific use case to me, and I believe raw_smp_processor_id() correctly > reflects the design intent by simply acquiring a CPU number without > debug checks. Thanks, I wasn't aware of the old discussion. If user-space can tolerate, than it's fine. Would you mind updating the comment above the changed line? It talks about not allocating memory in atomic context, so migrate_disable() would solve this. Just mention that it can't block CPU hotplug events either and user-space can handle spurious errors. With that: Reviewed-by: Catalin Marinas