[PATCH v4] scsi: libsas: Allocation SMP request is aligned to ARCH_DMA_MINALIGN

[PATCH v4] scsi: libsas: Allocation SMP request is aligned to ARCH_DMA_MINALIGN

[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.

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;
-- 
2.33.0

Re: [PATCH v4] scsi: libsas: Allocation SMP request is aligned to ARCH_DMA_MINALIGN

[John Garry]

On 28/03/2024 09:06, 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.

I'd say that we must align to at least ARCH_DMA_MINALIGN for memory 
which we want to map for DMA. ARCH_DMA_MINALIGN would never be less than 
the 16B requirement for hisi_sas, so just align to ARCH_DMA_MINALIGN.

> 
> Link: https://urldefense.com/v3/__https://lkml.kernel.org/r/20230612153201.554742-1-catalin.marinas@arm.com__;!!ACWV5N9M2RV99hQ!LbkCJSfklWds8mk0UGjtg0qRNpWuAc-ibudDMl7sI_Qip4Hd6WNqHZmRbuJfObd4fcZXj0sC8nGTs1UbA5PlCA$  [1]
> Signed-off-by: Yihang Li <liyihang9@huawei.com>
> Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

Reviewed-by: John Garry <john.g.garry@oracle.com>

> ---
> 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;

Re: [PATCH v4] scsi: libsas: Allocation SMP request is aligned to ARCH_DMA_MINALIGN

[Jason Yan]

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

Re: [PATCH v4] scsi: libsas: Allocation SMP request is aligned to ARCH_DMA_MINALIGN

[Martin K. Petersen]

On Thu, 28 Mar 2024 17:06:26 +0800, 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.
> 
> [...]

Applied to 6.9/scsi-fixes, thanks!

[1/1] scsi: libsas: Allocation SMP request is aligned to ARCH_DMA_MINALIGN
      https://git.kernel.org/mkp/scsi/c/e675a4fd6d1f

-- 
Martin K. Petersen	Oracle Linux Engineering