| Message ID | 20240326124358.2466259-1-liyihang9@huawei.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] scsi: libsas: Allocation SMP request is aligned to ARCH_DMA_MINALIGN | expand |
On 2024/3/28 14:35, Christoph Hellwig wrote: > On Tue, Mar 26, 2024 at 01:32:09PM +0000, John Garry wrote: >>>> + u8 *p; >>>> + >>>> + size = ALIGN(size, ARCH_DMA_MINALIGN); >> >> >> If this is a hisi_sas requirement, then why use ARCH_DMA_MINALIGN and not >> 16B as minimum alignment? >> >> Or are we really talking about an arch requirement? > > One thing is that we should never allocate unaligned memory for > anything DMA mapped, or data will be corrupted by non-coherent DMA. > So ARCH_DMA_MINALIGN needs to be here. If specific hardware has > further requirements we'll need to communicated it through a field > or op vector. Got it. Looks like it's still going to be aligned to ARCH_DMA_MINALIGN. Thanks, Yihang > > > . >
On Thu, Mar 28, 2024 at 04:23:22PM +0900, Damien Le Moal wrote: > But I thought that the original issue was that some arch have ARCH_DMA_MINALIGN > down to 8B but hisi driver needs at least 16 ? > > So in the end, you need something like: > > size = ALIGN(size, max(16, ARCH_DMA_MINALIGN)); > > no ? I don't think we ever have an 8 byte dma minalign. With 8-byte aligned addresses dma_mapping_error could run into problems.
On Thu, Mar 28, 2024 at 04:36:12PM +0900, Damien Le Moal wrote:
> My bad: it is kmalloc() that can return something aligned to 8B...
Yes, that's new on arm64, and possibly soon riscv.
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); if (p) p[0] = SMP_REQUEST; return p;
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> --- 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(-)