linux-kernel - Re: [PATCH] iommu/arm-smmu-v3: Fix L1 stream table index calculation for AmpereOne

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Message-ID: <d4b53bbb-333a-45b9-9eb0-23ddd0820a14@arm.com>
Date: Wed, 2 Oct 2024 17:58:09 +0100
From: James Morse <james.morse@....com>
To: Yang Shi <yang@...amperecomputing.com>, jgg@...pe.ca,
 nicolinc@...dia.com, will@...nel.org, robin.murphy@....com
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/arm-smmu-v3: Fix L1 stream table index calculation
 for AmpereOne

Hello!

On 01/10/2024 19:03, Yang Shi wrote:
> The commit ce410410f1a7 ("iommu/arm-smmu-v3: Add arm_smmu_strtab_l1/2_idx()")
> calculated the last index of L1 stream table by 1 << smmu->sid_bits. 1
> is 32 bit value.
> However AmpereOne has 32-bit stream id size.  This resulted in
> ouf-of-bound shift.  The disassembly of shift is:
> 
>     ldr     w2, [x19, 828]  //, smmu_7(D)->sid_bits
>     mov     w20, 1
>     lsl     w20, w20, w2
> 
> According to ARM spec, if the registers are 32 bit, the instruction actually
> does:
>     dest = src << (shift % 32)
> 
> So it actually shifted by zero bit.
> 
> This caused v6.12-rc1 failed to boot on AmpereOne

Same here - one of arm's reference designs prints 1 giga-tonne of:
| arm-smmu-v3 arm-smmu-v3.5.auto: event 0x02 received:
| arm-smmu-v3 arm-smmu-v3.5.auto:  0x0000c90000000002
| arm-smmu-v3 arm-smmu-v3.5.auto:  0x0000000000000000
| arm-smmu-v3 arm-smmu-v3.5.auto:  0x0000000000000000
| arm-smmu-v3 arm-smmu-v3.5.auto:  0x0000000000000000

during boot - then fails to find the nvme.
Bisect points to ce410410f1a7, and the below diff fixes it.

> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index 737c5b882355..01a2faee04bc 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -3625,7 +3625,7 @@ static int arm_smmu_init_strtab_2lvl(struct arm_smmu_device *smmu)
>  	u32 l1size;
>  	struct arm_smmu_strtab_cfg *cfg = &smmu->strtab_cfg;
>  	unsigned int last_sid_idx =
> -		arm_smmu_strtab_l1_idx((1 << smmu->sid_bits) - 1);
> +		arm_smmu_strtab_l1_idx((1UL << smmu->sid_bits) - 1);
>  
>  	/* Calculate the L1 size, capped to the SIDSIZE. */
>  	cfg->l2.num_l1_ents = min(last_sid_idx + 1, STRTAB_MAX_L1_ENTRIES);


Tested-by: James Morse <james.morse@....com>


Thanks,

James