linux-kernel - Re: [PATCH] iommu/arm-smmu-v3: Fix incorrect fields being passed to prefetch command

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Message-ID: <20190628095250.bzq4aqyuczt47y4i@willie-the-truck>
Date:   Fri, 28 Jun 2019 10:52:51 +0100
From:   Will Deacon <will@...nel.org>
To:     Pratyush Yadav <p-yadav1@...com>
Cc:     robin.murphy@....com, joro@...tes.org,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        wmills@...com, nsekhar@...com, lokeshvutla@...com
Subject: Re: [PATCH] iommu/arm-smmu-v3: Fix incorrect fields being passed to
 prefetch command

On Fri, Jun 28, 2019 at 02:39:53PM +0530, Pratyush Yadav wrote:
> According to the SMMUv3 spec [0] section 4.2.1, command 0x1
> (CMD_PREFETCH_CONFIG) does not take address and size as parameters. It
> only takes  StreamID, SSec, SubstreamID, and SSV. Address and Size are
> parameters for command 0x2 (CMD_PREFETCH_ADDR).
> 
> Tested on kernel 4.19 on TI J721E SOC.
> 
> [0] https://static.docs.arm.com/ihi0070/a/IHI_0070A_SMMUv3.pdf
> 
> Signed-off-by: Pratyush Yadav <p-yadav1@...com>
> ---
>  drivers/iommu/arm-smmu-v3.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index 4d5a694f02c2..2d4dfd909436 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -413,6 +413,7 @@ struct arm_smmu_cmdq_ent {
>  	/* Command-specific fields */
>  	union {
>  		#define CMDQ_OP_PREFETCH_CFG	0x1
> +		#define CMDQ_OP_PREFETCH_ADDR	0x2
>  		struct {
>  			u32			sid;
>  			u8			size;
> @@ -805,10 +806,12 @@ static int arm_smmu_cmdq_build_cmd(u64 *cmd, struct arm_smmu_cmdq_ent *ent)
>  	case CMDQ_OP_TLBI_EL2_ALL:
>  	case CMDQ_OP_TLBI_NSNH_ALL:
>  		break;
> -	case CMDQ_OP_PREFETCH_CFG:
> -		cmd[0] |= FIELD_PREP(CMDQ_PREFETCH_0_SID, ent->prefetch.sid);
> +	case CMDQ_OP_PREFETCH_ADDR:
>  		cmd[1] |= FIELD_PREP(CMDQ_PREFETCH_1_SIZE, ent->prefetch.size);
>  		cmd[1] |= ent->prefetch.addr & CMDQ_PREFETCH_1_ADDR_MASK;
> +		/* Fallthrough */
> +	case CMDQ_OP_PREFETCH_CFG:
> +		cmd[0] |= FIELD_PREP(CMDQ_PREFETCH_0_SID, ent->prefetch.sid);

Hmm, but there's no issue here because the onus is on the caller not to
initialise size and addr if they are using PREFETCH_CFG (and this is
currently the case). Are you seeing a problem in practice?

I'm happy to take a patch adding support for PREFETCH_ADDR, but we'd need
a caller first.

Also -- fancy sending me a board? ;)

Will