On 2021-07-06 14:24, Will Deacon wrote:
On Tue, Jul 06, 2021 at 06:48:48AM +0200, Christoph Hellwig wrote:
On Mon, Jul 05, 2021 at 08:03:52PM +0100, Will Deacon wrote:
So at this point, the AMD IOMMU driver does:
swiotlb = (iommu_default_passthrough() || sme_me_mask) ? 1 : 0;
where 'swiotlb' is a global variable indicating whether or not swiotlb is in use. It's picked up a bit later on by pci_swiotlb_late_init(), which will call swiotlb_exit() if 'swiotlb' is false.
Now, that used to work fine, because swiotlb_exit() clears 'io_tlb_default_mem' to NULL, but now with the restricted DMA changes, I think that all the devices which have successfully probed beforehand will have stale pointers to the freed structure in their 'dev->dma_io_tlb_mem' field.
Yeah. I don't think we can do that anymore, and I also think it is a bad idea to start with.
I've had a crack at reworking things along the following lines:
io_tlb_default_mem now lives in the BSS, the flexible array member is now a pointer and that part is allocated dynamically (downside of this is an extra indirection to get at the slots).
io_tlb_default_mem.nslabs tells you whether the thing is valid
swiotlb_exit() frees the slots array and clears the rest of the structure to 0. I also extended it to free the actual slabs, but I'm not sure why it wasn't doing that before.
So a non-NULL dev->dma_io_tlb_mem should always be valid to follow.
FWIW I was pondering the question of whether to do something along those lines or just scrap the default assignment entirely, so since I hadn't got round to saying that I've gone ahead and hacked up the alternative (similarly untested) for comparison :)
TBH I'm still not sure which one I prefer...
Robin.
----->8----- diff --git a/drivers/base/core.c b/drivers/base/core.c index ea5b85354526..394abf184c1a 100644 --- a/drivers/base/core.c +++ b/drivers/base/core.c @@ -2847,9 +2847,6 @@ void device_initialize(struct device *dev) defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL) dev->dma_coherent = dma_default_coherent; #endif -#ifdef CONFIG_SWIOTLB - dev->dma_io_tlb_mem = io_tlb_default_mem; -#endif } EXPORT_SYMBOL_GPL(device_initialize);
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h index 39284ff2a6cd..620f16d89a98 100644 --- a/include/linux/swiotlb.h +++ b/include/linux/swiotlb.h @@ -107,16 +107,21 @@ struct io_tlb_mem { }; extern struct io_tlb_mem *io_tlb_default_mem;
+static inline struct io_tlb_mem *dev_iotlb_mem(struct device *dev) +{ + return dev->dma_io_tlb_mem ?: io_tlb_default_mem; +} + static inline bool is_swiotlb_buffer(struct device *dev, phys_addr_t paddr) { - struct io_tlb_mem *mem = dev->dma_io_tlb_mem; + struct io_tlb_mem *mem = dev_iotlb_mem(dev);
return mem && paddr >= mem->start && paddr < mem->end; }
static inline bool is_swiotlb_force_bounce(struct device *dev) { - struct io_tlb_mem *mem = dev->dma_io_tlb_mem; + struct io_tlb_mem *mem = dev_iotlb_mem(dev);
return mem && mem->force_bounce; } @@ -167,7 +172,7 @@ bool swiotlb_free(struct device *dev, struct page *page, size_t size);
static inline bool is_swiotlb_for_alloc(struct device *dev) { - return dev->dma_io_tlb_mem->for_alloc; + return dev_iotlb_mem(dev)->for_alloc; } #else static inline struct page *swiotlb_alloc(struct device *dev, size_t size) diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index b7f76bca89bf..f4942149f87d 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -359,7 +359,7 @@ static unsigned int swiotlb_align_offset(struct device *dev, u64 addr) static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size, enum dma_data_direction dir) { - struct io_tlb_mem *mem = dev->dma_io_tlb_mem; + struct io_tlb_mem *mem = dev_iotlb_mem(dev); int index = (tlb_addr - mem->start) >> IO_TLB_SHIFT; phys_addr_t orig_addr = mem->slots[index].orig_addr; size_t alloc_size = mem->slots[index].alloc_size; @@ -440,7 +440,7 @@ static unsigned int wrap_index(struct io_tlb_mem *mem, unsigned int index) static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr, size_t alloc_size) { - struct io_tlb_mem *mem = dev->dma_io_tlb_mem; + struct io_tlb_mem *mem = dev_iotlb_mem(dev); unsigned long boundary_mask = dma_get_seg_boundary(dev); dma_addr_t tbl_dma_addr = phys_to_dma_unencrypted(dev, mem->start) & boundary_mask; @@ -522,7 +522,7 @@ phys_addr_t swiotlb_tbl_map_single(struct device *dev, phys_addr_t orig_addr, size_t mapping_size, size_t alloc_size, enum dma_data_direction dir, unsigned long attrs) { - struct io_tlb_mem *mem = dev->dma_io_tlb_mem; + struct io_tlb_mem *mem = dev_iotlb_mem(dev); unsigned int offset = swiotlb_align_offset(dev, orig_addr); unsigned int i; int index; @@ -565,7 +565,7 @@ phys_addr_t swiotlb_tbl_map_single(struct device *dev, phys_addr_t orig_addr,
static void swiotlb_release_slots(struct device *dev, phys_addr_t tlb_addr) { - struct io_tlb_mem *mem = dev->dma_io_tlb_mem; + struct io_tlb_mem *mem = dev_iotlb_mem(dev); unsigned long flags; unsigned int offset = swiotlb_align_offset(dev, tlb_addr); int index = (tlb_addr - offset - mem->start) >> IO_TLB_SHIFT; @@ -682,7 +682,7 @@ size_t swiotlb_max_mapping_size(struct device *dev)
bool is_swiotlb_active(struct device *dev) { - return dev->dma_io_tlb_mem != NULL; + return dev_iotlb_mem(dev) != NULL; } EXPORT_SYMBOL_GPL(is_swiotlb_active);
@@ -729,7 +729,7 @@ static void rmem_swiotlb_debugfs_init(struct reserved_mem *rmem)
struct page *swiotlb_alloc(struct device *dev, size_t size) { - struct io_tlb_mem *mem = dev->dma_io_tlb_mem; + struct io_tlb_mem *mem = dev_iotlb_mem(dev); phys_addr_t tlb_addr; int index;
@@ -792,7 +792,7 @@ static int rmem_swiotlb_device_init(struct reserved_mem *rmem, static void rmem_swiotlb_device_release(struct reserved_mem *rmem, struct device *dev) { - dev->dma_io_tlb_mem = io_tlb_default_mem; + dev->dma_io_tlb_mem = NULL; }
static const struct reserved_mem_ops rmem_swiotlb_ops = {