swiotlb: determine potential physical address limit

The value returned by default_swiotlb_limit() should be constant, because
it is used to decide whether DMA can be used. To allow allocating memory
pools on the fly, use the maximum possible physical address rather than the
highest address used by the default pool.

For swiotlb_init_remap(), this is either an arch-specific limit used by
memblock_alloc_low(), or the highest directly mapped physical address if
the initialization flags include SWIOTLB_ANY. For swiotlb_init_late(), the
highest address is determined by the GFP flags.

Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Author: Petr Tesarik

include/linux/swiotlb.h

@@ -109,6 +109,7 @@ struct io_tlb_pool {
  * @force_bounce: %true if swiotlb bouncing is forced
  * @for_alloc:  %true if the pool is used for memory allocation
  * @can_grow:	%true if more pools can be allocated dynamically.
+ * @phys_limit:	Maximum allowed physical address.
  * @total_used:	The total number of slots in the pool that are currently used
  *		across all areas. Used only for calculating used_hiwater in
  *		debugfs.
@@ -123,6 +124,7 @@ struct io_tlb_mem {
 	bool for_alloc;
 #ifdef CONFIG_SWIOTLB_DYNAMIC
 	bool can_grow;
+	u64 phys_limit;
 #endif
 #ifdef CONFIG_DEBUG_FS
 	atomic_long_t total_used;

kernel/dma/swiotlb.c

@@ -334,6 +334,10 @@ void __init swiotlb_init_remap(bool addressing_limit, unsigned int flags,
 #ifdef CONFIG_SWIOTLB_DYNAMIC
 	if (!remap)
 		io_tlb_default_mem.can_grow = true;
+	if (flags & SWIOTLB_ANY)
+		io_tlb_default_mem.phys_limit = virt_to_phys(high_memory - 1);
+	else
+		io_tlb_default_mem.phys_limit = ARCH_LOW_ADDRESS_LIMIT;
 #endif
 
 	if (!default_nareas)
@@ -409,6 +413,12 @@ int swiotlb_init_late(size_t size, gfp_t gfp_mask,
 #ifdef CONFIG_SWIOTLB_DYNAMIC
 	if (!remap)
 		io_tlb_default_mem.can_grow = true;
+	if (IS_ENABLED(CONFIG_ZONE_DMA) && (gfp_mask & __GFP_DMA))
+		io_tlb_default_mem.phys_limit = DMA_BIT_MASK(zone_dma_bits);
+	else if (IS_ENABLED(CONFIG_ZONE_DMA32) && (gfp_mask & __GFP_DMA32))
+		io_tlb_default_mem.phys_limit = DMA_BIT_MASK(32);
+	else
+		io_tlb_default_mem.phys_limit = virt_to_phys(high_memory - 1);
 #endif
 
 	if (!default_nareas)
@@ -1397,7 +1407,11 @@ phys_addr_t default_swiotlb_base(void)
  */
 phys_addr_t default_swiotlb_limit(void)
 {
+#ifdef CONFIG_SWIOTLB_DYNAMIC
+	return io_tlb_default_mem.phys_limit;
+#else
 	return io_tlb_default_mem.defpool.end - 1;
+#endif
 }
 
 #ifdef CONFIG_DEBUG_FS