linux-kernel - Re: [PATCH v2] scsi: libsas: Allocation SMP request is aligned to ARCH_DMA

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Message-ID: <5b5b9392-7fd2-4c87-8e41-5e54adf20003@kernel.org>
Date: Tue, 26 Mar 2024 22:14:11 +0900
From: Damien Le Moal <dlemoal@...nel.org>
To: Yihang Li <liyihang9@...wei.com>, john.g.garry@...cle.com,
 yanaijie@...wei.com, jejb@...ux.ibm.com, martin.petersen@...cle.com,
 chenxiang66@...ilicon.com
Cc: linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
 linuxarm@...wei.com, prime.zeng@...wei.com, yangxingui@...wei.com
Subject: Re: [PATCH v2] scsi: libsas: Allocation SMP request is aligned to
 ARCH_DMA_MINALIGN

On 3/26/24 21:43, 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@...wei.com>
> ---
> Changes since v1:
> - Directly modify alloc_smp_req() instead of using handler callback.
> ---
>  drivers/scsi/libsas/sas_expander.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/libsas/sas_expander.c b/drivers/scsi/libsas/sas_expander.c
> index a2204674b680..941abc7298df 100644
> --- a/drivers/scsi/libsas/sas_expander.c
> +++ b/drivers/scsi/libsas/sas_expander.c
> @@ -135,7 +135,10 @@ 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;
> +
> +	size = ALIGN(size, ARCH_DMA_MINALIGN);
> +	p = kzalloc(size, GFP_KERNEL);

Nit: why not:

	p = kzalloc(ALIGN(size, ARCH_DMA_MINALIGN), GFP_KERNEL);

>  	if (p)
>  		p[0] = SMP_REQUEST;
>  	return p;

Otherwise looks OK to me.

John,

Unrelated to this patch, but I wonder if the GFP_KERNEL used here shouldn't be
GFP_NOIO... Is this ever called in the IO path or error recovery ?

-- 
Damien Le Moal
Western Digital Research