Thread (19 messages) 19 messages, 4 authors, 2021-06-17

Re: [PATCH v12 06/12] swiotlb: Use is_swiotlb_force_bounce for swiotlb data bouncing

From: Stefano Stabellini <sstabellini@kernel.org>
Date: 2021-06-17 00:47:12
Also in: dri-devel, intel-gfx, linux-devicetree, linux-iommu, linux-pci, lkml, xen-devel

On Wed, 16 Jun 2021, Claire Chang wrote:
quoted hunk ↗ jump to hunk
Propagate the swiotlb_force into io_tlb_default_mem->force_bounce and
use it to determine whether to bounce the data or not. This will be
useful later to allow for different pools.

Signed-off-by: Claire Chang <redacted>
---
 include/linux/swiotlb.h | 11 +++++++++++
 kernel/dma/direct.c     |  2 +-
 kernel/dma/direct.h     |  2 +-
 kernel/dma/swiotlb.c    |  4 ++++
 4 files changed, 17 insertions(+), 2 deletions(-)
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index dd1c30a83058..8d8855c77d9a 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -84,6 +84,7 @@ extern enum swiotlb_force swiotlb_force;
  *		unmap calls.
  * @debugfs:	The dentry to debugfs.
  * @late_alloc:	%true if allocated using the page allocator
+ * @force_bounce: %true if swiotlb bouncing is forced
  */
 struct io_tlb_mem {
 	phys_addr_t start;
@@ -94,6 +95,7 @@ struct io_tlb_mem {
 	spinlock_t lock;
 	struct dentry *debugfs;
 	bool late_alloc;
+	bool force_bounce;
 	struct io_tlb_slot {
 		phys_addr_t orig_addr;
 		size_t alloc_size;
@@ -109,6 +111,11 @@ static inline bool is_swiotlb_buffer(struct device *dev, phys_addr_t paddr)
 	return mem && paddr >= mem->start && paddr < mem->end;
 }
 
+static inline bool is_swiotlb_force_bounce(struct device *dev)
+{
+	return dev->dma_io_tlb_mem->force_bounce;
+}
 void __init swiotlb_exit(void);
 unsigned int swiotlb_max_segment(void);
 size_t swiotlb_max_mapping_size(struct device *dev);
@@ -120,6 +127,10 @@ static inline bool is_swiotlb_buffer(struct device *dev, phys_addr_t paddr)
 {
 	return false;
 }
+static inline bool is_swiotlb_force_bounce(struct device *dev)
+{
+	return false;
+}
 static inline void swiotlb_exit(void)
 {
 }
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 7a88c34d0867..a92465b4eb12 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -496,7 +496,7 @@ size_t dma_direct_max_mapping_size(struct device *dev)
 {
 	/* If SWIOTLB is active, use its maximum mapping size */
 	if (is_swiotlb_active(dev) &&
-	    (dma_addressing_limited(dev) || swiotlb_force == SWIOTLB_FORCE))
+	    (dma_addressing_limited(dev) || is_swiotlb_force_bounce(dev)))
 		return swiotlb_max_mapping_size(dev);
 	return SIZE_MAX;
 }
diff --git a/kernel/dma/direct.h b/kernel/dma/direct.h
index 13e9e7158d94..4632b0f4f72e 100644
--- a/kernel/dma/direct.h
+++ b/kernel/dma/direct.h
@@ -87,7 +87,7 @@ static inline dma_addr_t dma_direct_map_page(struct device *dev,
 	phys_addr_t phys = page_to_phys(page) + offset;
 	dma_addr_t dma_addr = phys_to_dma(dev, phys);
 
-	if (unlikely(swiotlb_force == SWIOTLB_FORCE))
+	if (is_swiotlb_force_bounce(dev))
 		return swiotlb_map(dev, phys, size, dir, attrs);

 	if (unlikely(!dma_capable(dev, dma_addr, size, true))) {
Should we also make the same change in
drivers/xen/swiotlb-xen.c:xen_swiotlb_map_page ?

If I make that change, I can see that everything is working as
expected for a restricted-dma device with Linux running as dom0 on Xen.
However, is_swiotlb_force_bounce returns non-zero even for normal
non-restricted-dma devices. That shouldn't happen, right?

It looks like struct io_tlb_slot is not zeroed on allocation.
Adding memset(mem, 0x0, struct_size) in swiotlb_late_init_with_tbl
solves the issue.

With those two changes, the series passes my tests and you can add my
tested-by.
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