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

From: Nicolin Chen <nicolinc@nvidia.com>
To: Will Deacon <will@kernel.org>
Cc: zhurui <zhurui3@huawei.com>,
	<linux-arm-kernel@lists.infradead.org>, <iommu@lists.linux.dev>,
	<linux-kernel@vger.kernel.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Joerg Roedel <joro@8bytes.org>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	Yicong Yang <yangyicong@hisilicon.com>,
	Tomas Krcka <krckatom@amazon.de>,
	"Jean-Philippe Brucker" <jean-philippe@linaro.org>
Subject: Re: [PATCH v2 1/1] iommu/arm-smmu-v3: Fix error case of range command
Date: Fri, 4 Aug 2023 11:30:03 -0700	[thread overview]
Message-ID: <ZM1DqxXcBT2SOs8/@Asurada-Nvidia> (raw)
In-Reply-To: <20230804165225.GF30679@willie-the-truck>

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

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