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 8BEB2C43458 for ; Fri, 3 Jul 2026 14:30:52 +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:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=LOmRARbfHQRat7CY7N1DEP0Wd4q+JhZjRA94tD7uHkw=; b=VpXqF+Eev0pYjWxiwQekYzJOt2 sl7NHdL2kMH3khYu7sIa0kUf553pQ7Qk3gVxLNyWsj5CMGKhFEXQF7VhFxYnkAnDJ1d6AYXEPeSQ2 WzW5gg40Qo4De2s7U9BiVIu+2IpfVPSoH+LzpwawEc0NhBWuobgXMOXQUGk2WRIgdVgRJOa7PLeMx N07dZQbTntQT9FJ19FbxrD3atnJmIO3bk/qwoNQDfzCWdbh0mHnK5z77gd1qelfK83+aUhgPBt8pi kGqfvp/OGOi/9+0TbUuk/e3nPUXfBnolTqQAiBJ7tNXjTdLUTBMURz2xxXxFHQVEAjwNpu7LbTKkw WJW4+EEg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wfeuj-00000007Gku-2MKi; Fri, 03 Jul 2026 14:30:45 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wfeug-00000007GhT-2byP for linux-arm-kernel@lists.infradead.org; Fri, 03 Jul 2026 14:30:43 +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 8EB311EA6; Fri, 3 Jul 2026 07:30:37 -0700 (PDT) Received: from [10.1.29.35] (e122027.cambridge.arm.com [10.1.29.35]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1BD453F905; Fri, 3 Jul 2026 07:30:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1783089041; bh=OBodCYctTbXb2+xwe93dlNahekq1513+ys1RFuz3eN4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=LXkQlguHetum0QO+O0cg3QkU4xSAhPNX0ZTaRykp89mAmzE2/HR9f+dXlRFJJHxWu 2RAXIOZvA5wWON6YKdX5vbGXmB/ZASaOiE1IF0xqQSBwFojq0rlUQRiXU+DurxzGOf UZs2EJhidnN1qFKfzSrXtxqwLeKBgsvnxayZFcG4= Message-ID: Date: Fri, 3 Jul 2026 15:30:37 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] virt: arm-cca-guest: use migrate_disable() for attestation token requests To: Kohei Enju , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: Catalin Marinas , Will Deacon , Suzuki K Poulose , Sami Mujawar , Gavin Shan References: <20260612111007.49434-1-enju.kohei@fujitsu.com> From: Steven Price Content-Language: en-GB In-Reply-To: <20260612111007.49434-1-enju.kohei@fujitsu.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260703_073042_748731_DB8E428F X-CRM114-Status: GOOD ( 42.05 ) 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 12/06/2026 12:09, Kohei Enju wrote: > The RSI attestation token init and continue calls must be issued from > the same CPU. arm_cca_report_new() currently snapshots the CPU number > and uses smp_call_function_single() to issue those calls on that CPU. > > With CONFIG_DEBUG_PREEMPT=y, the smp_processor_id() call used for the > snapshot triggers a debug splat [0] because it runs in preemptible > context. The snapshot does not pin the task to that CPU; it is only used > to choose the target CPU for smp_call_function_single(), which can fail > if that CPU is no longer available. > > Use migrate_disable() and issue the token init and continue operations > directly, without the smp_call_function_single() callbacks. This keeps > the token request sequence on the same CPU while preserving a sleepable > context for the GFP_KERNEL allocations needed after the init call. > > [0] > BUG: using smp_processor_id() in preemptible [00000000] code: cca-workload-at/264 > caller is debug_smp_processor_id+0x20/0x30 > CPU: 0 UID: 0 PID: 264 Comm: cca-workload-at Not tainted 7.1.0-rc1-00044-g55542ab273f2 #80 PREEMPT(lazy) > Hardware name: linux,dummy-virt (DT) > Call trace: > [...] > check_preemption_disabled+0xd8/0xf8 > debug_smp_processor_id+0x20/0x30 > arm_cca_report_new+0x48/0x278 > tsm_report_read+0x154/0x1f8 > tsm_report_outblob_read+0x20/0x38 > configfs_bin_read_iter+0x118/0x208 > vfs_read+0x220/0x318 > [...] > > Fixes: 7999edc484ca ("virt: arm-cca-guest: TSM_REPORT support for realms") > Signed-off-by: Kohei Enju LGTM Reviewed-by: Steven Price > --- > Changes: > v3: > - Switch to migrate_disable() and call RSI directly, removing > smp_call_function_single() (Will, Suzuki) > - Remove arm_cca_attestation_init() helper and unused fields from > arm_cca_token_info > - Drop Reviewed-by tags since the approach changed from v2 > v2: https://lore.kernel.org/linux-arm-kernel/20260519101217.155740-1-enju.kohei@fujitsu.com/ > - Add comment about why this path doesn't use migrate_disable() > v1: https://lore.kernel.org/linux-arm-kernel/20260518033157.1865498-1-enju.kohei@fujitsu.com/ > --- > .../virt/coco/arm-cca-guest/arm-cca-guest.c | 97 +++++++------------ > 1 file changed, 36 insertions(+), 61 deletions(-) > > 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 66d00b6ceb78..a38df08da6fa 100644 > --- a/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c > +++ b/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c > @@ -16,54 +16,38 @@ > > /** > * struct arm_cca_token_info - a descriptor for the token buffer. > - * @challenge: Pointer to the challenge data > - * @challenge_size: Size of the challenge data > * @granule: PA of the granule to which the token will be written > * @offset: Offset within granule to start of buffer in bytes > - * @result: result of rsi_attestation_token_continue operation > */ > struct arm_cca_token_info { > - void *challenge; > - unsigned long challenge_size; > phys_addr_t granule; > unsigned long offset; > - unsigned long result; > }; > > -static void arm_cca_attestation_init(void *param) > -{ > - struct arm_cca_token_info *info; > - > - info = (struct arm_cca_token_info *)param; > - > - info->result = rsi_attestation_token_init(info->challenge, > - info->challenge_size); > -} > - > /** > * arm_cca_attestation_continue - Retrieve the attestation token data. > * > - * @param: pointer to the arm_cca_token_info > + * @info: pointer to the arm_cca_token_info > * > * Attestation token generation is a long running operation and therefore > * the token data may not be retrieved in a single call. Moreover, the > * token retrieval operation must be requested on the same CPU on which the > * attestation token generation was initialised. > - * This helper function is therefore scheduled on the same CPU multiple > + * This helper function must therefore be executed on the same CPU multiple > * times until the entire token data is retrieved. > */ > -static void arm_cca_attestation_continue(void *param) > +static unsigned long > +arm_cca_attestation_continue(struct arm_cca_token_info *info) > { > + unsigned long ret; > unsigned long len; > unsigned long size; > - struct arm_cca_token_info *info; > - > - info = (struct arm_cca_token_info *)param; > > size = RSI_GRANULE_SIZE - info->offset; > - info->result = rsi_attestation_token_continue(info->granule, > - info->offset, size, &len); > + ret = rsi_attestation_token_continue(info->granule, info->offset, size, > + &len); > info->offset += len; > + return ret; > } > > /** > @@ -74,8 +58,8 @@ static void arm_cca_attestation_continue(void *param) > * > * Initialise the attestation token generation using the challenge data > * passed in the TSM descriptor. Allocate memory for the attestation token > - * and schedule calls to retrieve the attestation token on the same CPU > - * on which the attestation token generation was initialised. > + * and retrieve the attestation token on the same CPU on which the > + * attestation token generation was initialised. > * > * The challenge data must be at least 32 bytes and no more than 64 bytes. If > * less than 64 bytes are provided it will be zero padded to 64 bytes. > @@ -85,12 +69,11 @@ static void arm_cca_attestation_continue(void *param) > * * %-EINVAL - A parameter was not valid. > * * %-ENOMEM - Out of memory. > * * %-EFAULT - Failed to get IPA for memory page(s). > - * * A negative status code as returned by smp_call_function_single(). > */ > static int arm_cca_report_new(struct tsm_report *report, void *data) > { > - int ret; > - int cpu; > + int ret = 0; > + unsigned long rsi_result; > long max_size; > unsigned long token_size = 0; > struct arm_cca_token_info info; > @@ -103,37 +86,33 @@ static int arm_cca_report_new(struct tsm_report *report, void *data) > > /* > * The attestation token 'init' and 'continue' calls must be > - * performed on the same CPU. smp_call_function_single() is used > - * instead of simply calling get_cpu() because of the need to > - * allocate outblob based on the returned value from the 'init' > - * call and that cannot be done in an atomic context. > + * performed on the same CPU, so disable CPU migration around > + * those operations. > */ > - cpu = smp_processor_id(); > + migrate_disable(); > > - info.challenge = desc->inblob; > - info.challenge_size = desc->inblob_len; > - > - ret = smp_call_function_single(cpu, arm_cca_attestation_init, > - &info, true); > - if (ret) > - return ret; > - max_size = info.result; > - > - if (max_size <= 0) > - return -EINVAL; > + max_size = rsi_attestation_token_init(desc->inblob, desc->inblob_len); > + if (max_size <= 0) { > + ret = -EINVAL; > + goto exit_migrate_enable; > + } > > /* Allocate outblob */ > token = kvzalloc(max_size, GFP_KERNEL); > - if (!token) > - return -ENOMEM; > + if (!token) { > + ret = -ENOMEM; > + goto exit_migrate_enable; > + } > > /* > * Since the outblob may not be physically contiguous, use a page > * to bounce the buffer from RMM. > */ > buf = alloc_pages_exact(RSI_GRANULE_SIZE, GFP_KERNEL); > - if (!buf) > - return -ENOMEM; > + if (!buf) { > + ret = -ENOMEM; > + goto exit_migrate_enable; > + } > > /* Get the PA of the memory page(s) that were allocated */ > info.granule = (unsigned long)virt_to_phys(buf); > @@ -144,21 +123,15 @@ static int arm_cca_report_new(struct tsm_report *report, void *data) > info.offset = 0; > do { > /* > - * Schedule a call to retrieve a sub-granule chunk > - * of data per loop iteration. > + * Retrieve a sub-granule chunk of data per loop > + * iteration. > */ > - ret = smp_call_function_single(cpu, > - arm_cca_attestation_continue, > - (void *)&info, true); > - if (ret != 0) { > - token_size = 0; > - goto exit_free_granule_page; > - } > - } while (info.result == RSI_INCOMPLETE && > + rsi_result = arm_cca_attestation_continue(&info); > + } while (rsi_result == RSI_INCOMPLETE && > info.offset < RSI_GRANULE_SIZE); > > /* Break out in case of failure */ > - if (info.result != RSI_SUCCESS && info.result != RSI_INCOMPLETE) { > + if (rsi_result != RSI_SUCCESS && rsi_result != RSI_INCOMPLETE) { > ret = -ENXIO; > token_size = 0; > goto exit_free_granule_page; > @@ -173,12 +146,14 @@ static int arm_cca_report_new(struct tsm_report *report, void *data) > break; > memcpy(&token[token_size], buf, info.offset); > token_size += info.offset; > - } while (info.result == RSI_INCOMPLETE); > + } while (rsi_result == RSI_INCOMPLETE); > > report->outblob = no_free_ptr(token); > exit_free_granule_page: > report->outblob_len = token_size; > free_pages_exact(buf, RSI_GRANULE_SIZE); > +exit_migrate_enable: > + migrate_enable(); > return ret; > } >