[PATCH v3] scsi: libsas: Allocation SMP request is aligned to 16B

[PATCH v3] scsi: libsas: Allocation SMP request is aligned to 16B

[Yihang Li]

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.

So use 16B 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>
---
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..5ddbd00d5c76 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, 16), GFP_KERNEL);
 	if (p)
 		p[0] = SMP_REQUEST;
 	return p;
-- 
2.33.0

Re: [PATCH v3] scsi: libsas: Allocation SMP request is aligned to 16B

[Damien Le Moal]

On 3/28/24 15:26, 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.
> 
> So use 16B 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>

Looks OK to me.

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

> ---
> 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..5ddbd00d5c76 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, 16), GFP_KERNEL);
>  	if (p)
>  		p[0] = SMP_REQUEST;
>  	return p;

-- 
Damien Le Moal
Western Digital Research

Re: [PATCH v3] scsi: libsas: Allocation SMP request is aligned to 16B

[Christoph Hellwig]

> +	u8 *p = kzalloc(ALIGN(size, 16), GFP_KERNEL);

No, a magic undocumented 16 here max no sense at all.  See the
discussion on the previous iteration.