From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) (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 6F427613F for ; Wed, 9 Aug 2023 09:22:15 +0000 (UTC) Received: from canpemm500006.china.huawei.com (unknown [172.30.72.57]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4RLPcZ09HyzcdWm; Wed, 9 Aug 2023 17:18:38 +0800 (CST) Received: from [10.67.145.224] (10.67.145.224) by canpemm500006.china.huawei.com (7.192.105.130) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.27; Wed, 9 Aug 2023 17:22:06 +0800 Subject: Re: [PATCH v2 1/1] iommu/arm-smmu-v3: Fix error case of range command To: Robin Murphy , Will Deacon CC: Nicolin Chen , , , , Joerg Roedel , Lu Baolu , Jason Gunthorpe , Yicong Yang , Tomas Krcka , Jean-Philippe Brucker References: <1690784482-30028-1-git-send-email-wangwudi@hisilicon.com> <20230801085504.GA26130@willie-the-truck> <27c895b8-1fb0-be88-8bc3-878d754684c8@huawei.com> <20230804165225.GF30679@willie-the-truck> <015b4573-9d74-451b-8028-a1050ade7019@huawei.com> <661a7bb5-99e1-de16-d860-0cd17f7a0470@arm.com> <20230808162409.GB2890@willie-the-truck> <80ead8ee-4dbe-7b3c-44f5-944073a2a39d@arm.com> From: zhurui Message-ID: <412886be-644a-5b46-9bfa-1c9a358f9a5d@huawei.com> Date: Wed, 9 Aug 2023 17:22:06 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <80ead8ee-4dbe-7b3c-44f5-944073a2a39d@arm.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.145.224] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To canpemm500006.china.huawei.com (7.192.105.130) X-CFilter-Loop: Reflected On 2023/8/9 0:43, Robin Murphy wrote: > On 08/08/2023 5:24 pm, Will Deacon wrote: >> Hi Robin, >> >> On Mon, Aug 07, 2023 at 08:20:45PM +0100, Robin Murphy wrote: >>> On 2023-08-06 06:28, zhurui wrote: >>>> On 2023/8/5 2:30, Nicolin Chen wrote: >>>>> On Fri, Aug 04, 2023 at 05:52:25PM +0100, Will Deacon wrote: >>>>>> On Fri, Aug 04, 2023 at 05:31:20PM +0800, zhurui wrote: >>>>>>> When tg != 0 but ttl, scale, num all 0 in a range tlbi command, it >>>>>>> is reserved and will cause the CERROR_ILL error. This case means >>>>>>> that the size to be invalidated is only one page size, and the >>>>>>> range invalidation is meaningless here. So we set tg to 0 in this >>>>>>> case to do an non-range invalidation instead. >>>>> >>>>>>> @@ -1930,6 +1927,12 @@ static void __arm_smmu_tlb_inv_range(struct arm_smmu_cmdq_ent *cmd, >>>>>>>                           num = (num_pages >> scale) & CMDQ_TLBI_RANGE_NUM_MAX; >>>>>>>                           cmd->tlbi.num = num - 1; >>>>>>> >>>>>>> +                       /* Prevent error caused by one page tlbi with leaf 0 */ >>>>>>> +                       if (scale == 0 && num == 1 && cmd->tlbi.leaf == 0) >>>>>>> +                               cmd->tlbi.tg = 0; >>>>>> >>>>>> This should only be true for the last iteration, right (i.e. when num_pages >>>>>> == 1)? In which case, I'd prefer to leave the old code as-is and just add: >>>>>> >>>>>>           /* Single-page leaf invalidation requires a TG field of 0 */ >>>>>>           if (num_pages == 1 && !cmd->tlbi.leaf) >>>>>>                   cmd->tlbi.tg = 0;To Will and Nicolin, >>>> >>>> Not only the last iteration, it's the result of __ffs function. For example, if >>>> numpages is 33, then the value of __ffs(num_pages) is 0, so the value of scale >>>> is also 0. The value of num depends on CMDQ_TLBI_RANGE_NUM_MAX. That is, the >>>> maximum value of num is 31. Therefore, the final value of num is 1. >>>> So, if consider CMDQ_TLBI_RANGE_NUM_MAX, there will be some case not the last >>>> one page but the beginning pages. That's why I use scale and num as conditions, >>>> not num_pages. Then I should reassign tg based on the result. >>> >>> Yeah, I'd rather not downgrade to a non-range invalidate since that >>> complicates the reasoning for the errata affecting those. If the size of the >>> invalidation is equal to TG then it can only represent a single last-level >>> page, i.e. TTL=3, thus if it does warrant handling here then indeed >>> rearranging to base the condition on num_pages as well ought to suffice. >>> However, this is all still begging the question of where and why we're doing >>> a *non-leaf* invalidation that isn't aligned to the size of a table, because >>> that in itself doesn't make a whole heap of sense - my hunch is that that >>> wants figuring out and could probably be fixed at the source. >> >> Isn't that described above because we're using CMDQ_TLBI_RANGE_NUM_MAX >> to break up the range into separate commands? > > Not really, because if we're doing a genuine non-leaf invalidation of a table then it should be a block-aligned range that ought to fit in a single command and should certainly never involve a single-granule remainder. If we're doing non-leaf invalidations of things that logically don't need to be non-leaf, making them leaf would be the even better option. > I agree with Robin that if the caller is doing a genuine non-leaf invalidation of a table, it should not involve a single-granule tlbi. It seems that the caller only filter the block size, but not the address aligned or not maybe. >> Do you mind if I queue the patch as-is for now? I don't think the driver >> should be emitting illegal commands, and v2 of the patch does seem like >> the obvious thing to do. > > TBH I'd rather you just drop my patch if it's proven problematic, and I'll take another crack at it soon. The potential problems we introduce by using non-range invalidates on errata-affected MMU-700 revisions are worse than the almost-entirely-theoretical one I was trying to address. > If you all agree to roll back the problematic code, is the first patch be OK? Should I need to add some more descriptions to clarify this? Thanks, Zhurui.