From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 99816CD4F52 for ; Mon, 18 May 2026 12:33:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=ArlsmiOfKzo8EBsGIjgNNVOfRslHK0KLGN7eb26nmVw=; b=chNn/l4I7CnkfA9GvUSkj/LuTa wLE0rmvis1+LpNmjwLZS/UjLXdG3PvkjwcBRKf70rLc3IcRyd0fnMcV8xOyi2s5i2HxJtjNHfGp0B RG+Fb+aX/OtT5hwrfwejzUBq7nR/L1Sbr0iycZ7DGXxdVipDHkeOkXKFZC6rHU0z7iDYxVo6h9yB+ 2DjMTovMk7/poeLZfUMiV2CXP7+gN+kLoJKRUBzIrRp5i+isPiIix0pw90bF0qHnr7AqCdw6zcap2 yEgXzJpHhU3i1jhhUMM6e+oP6PL2LGC7Wam3hlevYD7CgTgU1SsVF9oieMk1RLIT0YQoTfwoqyGq+ pDJtTphQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wOx9t-0000000FeCX-2Q0M; Mon, 18 May 2026 12:33:21 +0000 Received: from casper.infradead.org ([2001:8b0:10b:1236::1]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wOx9s-0000000FeBn-0LbD for linux-arm-kernel@bombadil.infradead.org; Mon, 18 May 2026 12:33:20 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=ArlsmiOfKzo8EBsGIjgNNVOfRslHK0KLGN7eb26nmVw=; b=bYLpvamt21dwnJjdqFPuYrMcrS 0+fy+/acm38o0xVZSAjGGGQW1w460JrWOgxIyZ0vKoGbiZvCrXLzLrBNoXaOYcZWVNTqjTDAGTJSd qZGUAW/6cJfaZ03bH+1BDXNcb1O9V96vt+mMJmEyc5RUG3ylPIQgn+c/YlPdRNSvGzxliGioS3vMr nYGehCIVfk6OogiInylcW5n+NDGRPEwwkVFL9XaqDwbvc/15E1/U2Ya5vwZ2UOfV+gnd6Tzko1i/b 3kj+yfKyighkRjmtIgDLnzOqn07US5RHmPrsg7ZEDa9R8sUGOJvuv2RRs6P1jerGzw0zJG8NHRJa+ d5iuTeJA==; Received: from foss.arm.com ([217.140.110.172]) by casper.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wOx9n-00000004lUu-2RTR for linux-arm-kernel@lists.infradead.org; Mon, 18 May 2026 12:33:18 +0000 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 722CD2328; Mon, 18 May 2026 05:33:07 -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 8D4233F632; Mon, 18 May 2026 05:33:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1779107592; bh=xNPh5x7PUYf2b0+n2U0rK7b6u2aqB0hPpKpAY97oSLg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fxV9110zFT4QtYbjAKKw/u/WXWljCB9/fD8p/t3vV8MJurFeKElZJnwr8OE0wNL9+ rDbuhQfWsZYCRrkah6haXxGqI3cAZqgGi/gNxVc1uvrGhuSHoemIjYnfi7XIreIcNJ 3TgPNVpVqKZFF3Z9ekUgfa/XYHcrCcirN+9yuRxU= Date: Mon, 18 May 2026 13:33:09 +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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260518033157.1865498-1-enju.kohei@fujitsu.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260518_133315_923495_9732E4DC X-CRM114-Status: GOOD ( 23.07 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, May 18, 2026 at 12:31:31PM +0900, Kohei Enju wrote: > With CONFIG_DEBUG_PREEMPT=y, smp_processor_id() becomes an alias of > debug_smp_processor_id(). This debug function complains when certain > conditions that ensure CPU ID stability are not met, specifically when > it's called from a preemptible context. > > In arm_cca_report_new(), which runs in a preemptible context, > smp_processor_id() triggers a splat [0] due to this. > > However, the CPU ID obtained here is used as the target CPU for > smp_call_function_single() to designate a specific CPU for subsequent > operations, not to assert that the current thread will continue to > execute on the same CPU. Therefore, snapshotting the CPU ID itself is > correct, and thus there's no actual harm except for the splat. > > Use raw_smp_processor_id() instead, to directly retrieve the current CPU > ID without the debug checks, avoiding the unnecessary warning message > while preserving the correct functional behavior. > > [0] > BUG: using smp_processor_id() in preemptible [00000000] code: cca-workload-at/134 > caller is debug_smp_processor_id+0x20/0x2c > CPU: 0 UID: 0 PID: 134 Comm: cca-workload-at Not tainted 7.0.0-rc1-gc74a64d12073 #1 PREEMPT > Hardware name: linux,dummy-virt (DT) > Call trace: > [...] > check_preemption_disabled+0xf8/0x100 > debug_smp_processor_id+0x20/0x2c > arm_cca_report_new+0x54/0x230 > tsm_report_read+0x184/0x260 > tsm_report_outblob_read+0x18/0x38 > configfs_bin_read_iter+0xf4/0x1dc > vfs_read+0x230/0x31c > [...] > > Fixes: 7999edc484ca ("virt: arm-cca-guest: TSM_REPORT support for realms") > Signed-off-by: Kohei Enju > --- > drivers/virt/coco/arm-cca-guest/arm-cca-guest.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > 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. We should also look at the other unrelated findings in this function from Sashiko. -- Catalin