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

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Date:   Fri, 4 Aug 2023 11:30:03 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Will Deacon <will@...nel.org>
CC:     zhurui <zhurui3@...wei.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 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;

Is "!cmd->tlbi.leaf" to be "leaf" or "non-leaf"?

IIUIC, this "num_pages == 1" implies "NUM == 0, SCALE == 0" while
the "!cmd->tlbi.leaf" implies "TTL = 0b00", which in combination
would result in a CERROR_ILL mentioned by the spec?

I feel this could be more clear by just checking the three fields
following the spec...

Thanks
Nicolin