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Subject: Re: [PATCH v4] scsi: libsas: Allocation SMP request is aligned to
 ARCH_DMA_MINALIGN
To: Yihang Li <liyihang9@huawei.com>, <john.g.garry@oracle.com>,
	<jejb@linux.ibm.com>, <martin.petersen@oracle.com>, <dlemoal@kernel.org>,
	<chenxiang66@hisilicon.com>
CC: <linux-scsi@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<linuxarm@huawei.com>, <prime.zeng@huawei.com>, <yangxingui@huawei.com>
References: <20240328090626.621147-1-liyihang9@huawei.com>
From: Jason Yan <yanaijie@huawei.com>
Message-ID: <bd975860-8872-8bf9-0bd6-da69c2f2973d@huawei.com>
Date: Thu, 28 Mar 2024 17:49:58 +0800
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On 2024/3/28 17:06, Yihang Li wrote:
> This series [1] reducing the kmalloc() minimum alignment on arm64 to 8
> (from 128). In libsas, this will cause SMP requests to be 8-byte-aligned
> through kmalloc() allocation. However, for the hisi_sas hardware, all
> commands address must be 16-byte-aligned. Otherwise, the commands fail to
> be executed.
> 
> ARCH_DMA_MINALIGN represents the minimum (static) alignment for safe DMA
> operations, so use ARCH_DMA_MINALIGN as the alignment for SMP request.
> 
> Link: https://lkml.kernel.org/r/20230612153201.554742-1-catalin.marinas@arm.com [1]
> Signed-off-by: Yihang Li <liyihang9@huawei.com>
> Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
> ---
> Changes since v3:
> - Still aligned to ARCH_DMA_MINALIGN for safe DMA operations.
> 
> Changes since v2:
> - Use 16B as alignment for SMP requests instead of ARCH_DMA_MINALIGN.
> 
> Changes since v1:
> - Directly modify alloc_smp_req() instead of using handler callback.
> ---
>   drivers/scsi/libsas/sas_expander.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/libsas/sas_expander.c b/drivers/scsi/libsas/sas_expander.c
> index a2204674b680..c989d182fc75 100644
> --- a/drivers/scsi/libsas/sas_expander.c
> +++ b/drivers/scsi/libsas/sas_expander.c
> @@ -135,7 +135,7 @@ static int smp_execute_task(struct domain_device *dev, void *req, int req_size,
>   
>   static inline void *alloc_smp_req(int size)
>   {
> -	u8 *p = kzalloc(size, GFP_KERNEL);
> +	u8 *p = kzalloc(ALIGN(size, ARCH_DMA_MINALIGN), GFP_KERNEL);
>   	if (p)
>   		p[0] = SMP_REQUEST;
>   	return p;
> 

Reviewed-by: Jason Yan <yanaijie@huawei.com>

Thanks,
Jason