linux-kernel - Re: [v2 PATCH] iommu/arm-smmu-v3: Fix L1 stream table index calculation for 32-bit sid size

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Message-ID: <20241002181458.GK1369530@ziepe.ca>
Date: Wed, 2 Oct 2024 15:14:58 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Yang Shi <yang@...amperecomputing.com>
Cc: nicolinc@...dia.com, james.morse@....com, will@...nel.org,
	robin.murphy@....com, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH] iommu/arm-smmu-v3: Fix L1 stream table index
 calculation for 32-bit sid size

On Wed, Oct 02, 2024 at 10:55:14AM -0700, Yang Shi wrote:

> Using 64 bit immediate when doing shift can solve the problem.  The
> disassembly after the fix looks like:
>     ldr     w20, [x19, 828] //, smmu_7(D)->sid_bits
>     mov     x0, 1
>     lsl     x0, x0, x20
> 
> There are a couple of problematic places, extracted the shift into a helper.
> 
> [1] https://lore.kernel.org/lkml/d4b53bbb-333a-45b9-9eb0-23ddd0820a14@arm.com/
> Fixes: ce410410f1a7 ("iommu/arm-smmu-v3: Add arm_smmu_strtab_l1/2_idx()")
> Tested-by: James Morse <james.morse@....com>
> Signed-off-by: Yang Shi <yang@...amperecomputing.com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 8 +++++---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 5 +++++
>  2 files changed, 10 insertions(+), 3 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason