linux-kernel - Re: [PATCH v2 1/1] iommu/arm-smmu-v3: Fix error case of range command

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Date:   Tue, 8 Aug 2023 17:12:09 +0100
From:   Will Deacon <will@...nel.org>
To:     zhurui <zhurui3@...wei.com>
Cc:     Nicolin Chen <nicolinc@...dia.com>,
        linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Yicong Yang <yangyicong@...ilicon.com>,
        Tomas Krcka <krckatom@...zon.de>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [PATCH v2 1/1] iommu/arm-smmu-v3: Fix error case of range command

On Sun, Aug 06, 2023 at 01:28:04PM +0800, 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.

Yes, thanks, you're quite right. I'm not sure what I was thinking!

Will