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powerpc/iommu: bypass DMA APIs for coherent allocations for pre-mapped memory

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Leverage ARCH_HAS_DMA_MAP_DIRECT config option for coherent allocations as
well. This will bypass DMA ops for memory allocations that have been
pre-mapped.

Always set device bus_dma_limit when memory is pre-mapped. In some
architectures, like PowerPC, pmemory can be converted to regular memory via
daxctl command. This will gate the coherent allocations to pre-mapped RAM
only, by dma_coherent_ok().

Signed-off-by: Gaurav Batra <gbatra@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20251107161105.85999-1-gbatra@linux.ibm.com
This commit is contained in:
Gaurav Batra
2025-11-07 10:11:05 -06:00
committed by Madhavan Srinivasan
parent 20ab1d1126
commit 1471c517cf
4 changed files with 28 additions and 16 deletions
Download Patch File Download Diff File Expand all files Collapse all files

30
arch/powerpc/kernel/dma-iommu.c
View File

@@ -65,6 +65,21 @@ bool arch_dma_unmap_sg_direct(struct device *dev, struct scatterlist *sg,
return true;
}
bool arch_dma_alloc_direct(struct device *dev)
{
if (dev->dma_ops_bypass)
return true;
return false;
}
bool arch_dma_free_direct(struct device *dev, dma_addr_t dma_handle)
{
if (!dev->dma_ops_bypass)
return false;
return is_direct_handle(dev, dma_handle);
}
#endif /* CONFIG_ARCH_HAS_DMA_MAP_DIRECT */
/*
@@ -146,17 +161,12 @@ int dma_iommu_dma_supported(struct device *dev, u64 mask)
if (dev_is_pci(dev) && dma_iommu_bypass_supported(dev, mask)) {
/*
* dma_iommu_bypass_supported() sets dma_max when there is
* 1:1 mapping but it is somehow limited.
* ibm,pmemory is one example.
* fixed ops will be used for RAM. This is limited by
* bus_dma_limit which is set when RAM is pre-mapped.
*/
dev->dma_ops_bypass = dev->bus_dma_limit == 0;
if (!dev->dma_ops_bypass)
dev_warn(dev,
"iommu: 64-bit OK but direct DMA is limited by %llx\n",
dev->bus_dma_limit);
else
dev_dbg(dev, "iommu: 64-bit OK, using fixed ops\n");
dev->dma_ops_bypass = true;
dev_info(dev, "iommu: 64-bit OK but direct DMA is limited by %llx\n",
dev->bus_dma_limit);
return 1;
}

6
arch/powerpc/platforms/pseries/iommu.c
View File

@@ -1769,10 +1769,8 @@ out_failed:
out_unlock:
mutex_unlock(&dma_win_init_mutex);
/* If we have persistent memory and the window size is not big enough
* to directly map both RAM and vPMEM, then we need to set DMA limit.
*/
if (pmem_present && direct_mapping && len != MAX_PHYSMEM_BITS)
/* For pre-mapped memory, set bus_dma_limit to the max RAM */
if (direct_mapping)
dev->dev.bus_dma_limit = dev->dev.archdata.dma_offset +
(1ULL << max_ram_len);

4
include/linux/dma-map-ops.h
View File

@@ -395,11 +395,15 @@ bool arch_dma_map_sg_direct(struct device *dev, struct scatterlist *sg,
int nents);
bool arch_dma_unmap_sg_direct(struct device *dev, struct scatterlist *sg,
int nents);
bool arch_dma_alloc_direct(struct device *dev);
bool arch_dma_free_direct(struct device *dev, dma_addr_t dma_handle);
#else
#define arch_dma_map_phys_direct(d, a) (false)
#define arch_dma_unmap_phys_direct(d, a) (false)
#define arch_dma_map_sg_direct(d, s, n) (false)
#define arch_dma_unmap_sg_direct(d, s, n) (false)
#define arch_dma_alloc_direct(d) (false)
#define arch_dma_free_direct(d, a) (false)
#endif
#ifdef CONFIG_ARCH_HAS_SETUP_DMA_OPS

4
kernel/dma/mapping.c
View File

@@ -638,7 +638,7 @@ void *dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle,
/* let the implementation decide on the zone to allocate from: */
flag &= ~(__GFP_DMA | __GFP_DMA32 | __GFP_HIGHMEM);
if (dma_alloc_direct(dev, ops)) {
if (dma_alloc_direct(dev, ops) || arch_dma_alloc_direct(dev)) {
cpu_addr = dma_direct_alloc(dev, size, dma_handle, flag, attrs);
} else if (use_dma_iommu(dev)) {
cpu_addr = iommu_dma_alloc(dev, size, dma_handle, flag, attrs);
@@ -679,7 +679,7 @@ void dma_free_attrs(struct device *dev, size_t size, void *cpu_addr,
return;
debug_dma_free_coherent(dev, size, cpu_addr, dma_handle);
if (dma_alloc_direct(dev, ops))
if (dma_alloc_direct(dev, ops) || arch_dma_free_direct(dev, dma_handle))
dma_direct_free(dev, size, cpu_addr, dma_handle, attrs);
else if (use_dma_iommu(dev))
iommu_dma_free(dev, size, cpu_addr, dma_handle, attrs);