Re: [PATCH v2] riscv: mm: still create swiotlb buffer for kmalloc() bouncing if required
From: Alexandre Ghiti
Date: Tue Jan 16 2024 - 04:07:35 EST
On 16/01/2024 09:47, Jisheng Zhang wrote:
On Tue, Jan 16, 2024 at 09:23:47AM +0100, Alexandre Ghiti wrote:
Hi Jisheng,
On 02/12/2023 14:42, Jisheng Zhang wrote:
After commit f51f7a0fc2f4 ("riscv: enable DMA_BOUNCE_UNALIGNED_KMALLOC
for !dma_coherent"), for non-coherent platforms with less than 4GB
memory, we rely on users to pass "swiotlb=mmnn,force" kernel parameters
to enable DMA bouncing for unaligned kmalloc() buffers. Now let's go
further: If no bouncing needed for ZONE_DMA, let kernel automatically
allocate 1MB swiotlb buffer per 1GB of RAM for kmalloc() bouncing on
non-coherent platforms, so that no need to pass "swiotlb=mmnn,force"
any more.
IIUC, DMA_BOUNCE_UNALIGNED_KMALLOC is enabled for all non-coherent
platforms, even those with less than 4GB of memory. But the DMA bouncing
(which is necessary to enable kmalloc-8/16/32/96...) was not enabled unless
the user specified "swiotlb=mmnn,force" on the kernel command line. But does
that mean that if the user did not specify "swiotlb=mmnn,force", the
kmalloc-8/16/32/96 were enabled anyway and the behaviour was wrong (by lack
of DMA bouncing)?
Hi Alex,
For coherent platforms, kmalloc-8/16/32/96 was enabled.
For non-coherent platforms, if memory is more than 4GB, kmalloc-8/16/32/96 was enabled.
For non-coherent platforms, if memory is less than 4GB, kmalloc-8/16/32/96 was not
enabled. If users want kmalloc-8/16/32/96, we rely on users to pass "swiotlb=mmnn,force"
That's what I was unsure of :)
This patch tries to remove the "swiotlb=mmnn,force" requirement for the
last case. After this patch, kernel automatically uses "1MB swiotlb buffer per
1GB of RAM for kmalloc() bouncing" by default.
So this is an enhancement.
Great, so you can add:
Reviewed-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
Thanks,
Alex
Thanks
I'm trying to understand if that's a fix or an enhancement.
Thanks,
Alex
The math of "1MB swiotlb buffer per 1GB of RAM for kmalloc() bouncing"
is taken from arm64. Users can still force smaller swiotlb buffer by
passing "swiotlb=mmnn".
Signed-off-by: Jisheng Zhang <jszhang@xxxxxxxxxx>
---
since v2:
- fix build error if CONFIG_RISCV_DMA_NONCOHERENT=n
arch/riscv/include/asm/cache.h | 2 +-
arch/riscv/mm/init.c | 16 +++++++++++++++-
2 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/arch/riscv/include/asm/cache.h b/arch/riscv/include/asm/cache.h
index 2174fe7bac9a..570e9d8acad1 100644
--- a/arch/riscv/include/asm/cache.h
+++ b/arch/riscv/include/asm/cache.h
@@ -26,8 +26,8 @@
#ifndef __ASSEMBLY__
-#ifdef CONFIG_RISCV_DMA_NONCOHERENT
extern int dma_cache_alignment;
+#ifdef CONFIG_RISCV_DMA_NONCOHERENT
#define dma_get_cache_alignment dma_get_cache_alignment
static inline int dma_get_cache_alignment(void)
{
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 2e011cbddf3a..cbcb9918f721 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -162,11 +162,25 @@ static void print_vm_layout(void) { }
void __init mem_init(void)
{
+ bool swiotlb = max_pfn > PFN_DOWN(dma32_phys_limit);
#ifdef CONFIG_FLATMEM
BUG_ON(!mem_map);
#endif /* CONFIG_FLATMEM */
- swiotlb_init(max_pfn > PFN_DOWN(dma32_phys_limit), SWIOTLB_VERBOSE);
+ if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) && !swiotlb &&
+ dma_cache_alignment != 1) {
+ /*
+ * If no bouncing needed for ZONE_DMA, allocate 1MB swiotlb
+ * buffer per 1GB of RAM for kmalloc() bouncing on
+ * non-coherent platforms.
+ */
+ unsigned long size =
+ DIV_ROUND_UP(memblock_phys_mem_size(), 1024);
+ swiotlb_adjust_size(min(swiotlb_size_or_default(), size));
+ swiotlb = true;
+ }
+
+ swiotlb_init(swiotlb, SWIOTLB_VERBOSE);
memblock_free_all();
print_vm_layout();