Re: [PATCH v5 6/6] dma: swiotlb: Remove SWIOTLB_ANY

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
  Documentation/core-api/swiotlb.rst |  8 ++++----
  arch/powerpc/mm/mem.c              |  6 ++++--
  arch/riscv/mm/init.c               | 16 ----------------
  arch/s390/mm/init.c                |  2 +-
  arch/x86/kernel/pci-dma.c          |  2 +-
  include/linux/swiotlb.h            |  7 +++----
  kernel/dma/swiotlb.c               | 17 ++++++-----------
  7 files changed, 19 insertions(+), 39 deletions(-)

diff --git a/Documentation/core-api/swiotlb.rst b/Documentation/core-api/swiotlb.rst
index 71b4e4c27eb5..06d9f88fdf7b 100644
--- a/Documentation/core-api/swiotlb.rst
+++ b/Documentation/core-api/swiotlb.rst

@@ -148,10 +148,10 @@ may also be adjusted
  due to other conditions, such as running in a CoCo VM, as described above. If
  CONFIG_SWIOTLB_DYNAMIC is enabled, additional pools may be allocated later in
  the life of the system. Each pool must be a contiguous range of physical
-memory. The default pool is allocated below the 4 GiB physical address line so
-it works for devices that can only address 32-bits of physical memory (unless
-architecture-specific code provides the SWIOTLB_ANY flag). In a CoCo VM, the
-pool memory must be decrypted before swiotlb is used.
+memory. The default pool is allocated below the architecture's low address
+limit when it is needed for devices with limited DMA addressing. Otherwise,
+it may be allocated anywhere in directly mapped memory. In a CoCo VM, the pool
+memory must be decrypted before swiotlb is used.
  
  Each pool is divided into "slots" of size IO_TLB_SIZE, which is 2 KiB with
  current definitions. IO_TLB_SEGSIZE contiguous slots (128 slots) constitute

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 006ed41097e9..1bdea6c03848 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c

@@ -295,9 +295,11 @@ void __init arch_mm_preinit(void)
  		/*
  		 * Since the guest memory is inaccessible to the host,
  		 * devices always need to use the SWIOTLB buffer for DMA
-		 * even if dma_capable() says otherwise.
+		 * even if dma_capable() says otherwise. The hypervisor has
+		 * no addressing limitation, so the buffer may be allocated
+		 * anywhere.
  		 */
-		ppc_swiotlb_flags |= SWIOTLB_ANY;
+		ppc_swiotlb_flags &= ~SWIOTLB_INIT_ADDRESSING_LIMIT;
  	}
  
  	/*

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 96856114b387..734712230f35 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c

@@ -165,27 +165,11 @@ static void print_vm_layout(void) { }
  
  void __init arch_mm_preinit(void)
  {
-	bool swiotlb = max_pfn > PFN_DOWN(dma32_phys_limit) &&
-		       memblock_start_of_DRAM() < dma32_phys_limit;
  	unsigned int swiotlb_flags = SWIOTLB_VERBOSE;
  #ifdef CONFIG_FLATMEM
  	BUG_ON(!mem_map);
  #endif /* CONFIG_FLATMEM */
  
-	if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) && !swiotlb &&
-	    dma_cache_alignment != 1) {
-		/*
-		 * No 32-bit DMA bouncing needed (either all DRAM is within
-		 * the 32-bit limit, or it all starts above it), but
-		 * kmalloc() buffers whose sizes are not cache-line-aligned
-		 * still require bouncing for non-coherent DMA.  Use
-		 * SWIOTLB_ANY so that the buffer can be allocated from high
-		 * memory when DRAM starts above dma32_phys_limit.  Allocate
-		 * ~1 MB per 1 GB of RAM.
-		 */
-		swiotlb_flags |= SWIOTLB_ANY;
-	}
-
  	if ((max_pfn > PFN_DOWN(dma32_phys_limit)) &&
  	     (memblock_start_of_DRAM() < dma32_phys_limit))
  		swiotlb_flags |= SWIOTLB_INIT_ADDRESSING_LIMIT;

diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 78f507e24ceb..ce10292447f1 100644
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c

@@ -166,7 +166,7 @@ static void __init pv_init(void)
  	virtio_set_mem_acc_cb(virtio_require_restricted_mem_acc);
  
  	/* make sure bounce buffers are shared */
-	swiotlb_init(SWIOTLB_VERBOSE | SWIOTLB_ANY);
+	swiotlb_init(SWIOTLB_VERBOSE);
  	swiotlb_update_mem_attributes();
  }
  

diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index ce257b20ea9c..74e92b457758 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c

@@ -90,7 +90,7 @@ static void __init pci_xen_swiotlb_init(void)
  	/* Xen can use a SWIOTLB pool anywhere in directly mapped memory. */
  	x86_swiotlb_flags &= ~(SWIOTLB_INIT_ADDRESSING_LIMIT |
  			       SWIOTLB_INIT_DEFAULT_OFF);
-	x86_swiotlb_flags |= SWIOTLB_INIT_REMAP | SWIOTLB_ANY;
+	x86_swiotlb_flags |= SWIOTLB_INIT_REMAP;
  	swiotlb_init_remap(x86_swiotlb_flags, xen_swiotlb_fixup);
  	dma_ops = &xen_swiotlb_dma_ops;
  	if (IS_ENABLED(CONFIG_PCI))

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 466c33795db0..503e1446e0d8 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h

@@ -15,13 +15,12 @@ struct page;
  struct scatterlist;
  
  #define SWIOTLB_VERBOSE	(1 << 0) /* verbose initialization */
-#define SWIOTLB_ANY	(1 << 1) /* allow any memory for the buffer */
  /* Initialize a default-sized pool for devices with limited DMA addressing. */
-#define SWIOTLB_INIT_ADDRESSING_LIMIT	(1 << 2)
+#define SWIOTLB_INIT_ADDRESSING_LIMIT	(1 << 1)
  /* Initialize a default-sized pool that requires architecture remapping. */
-#define SWIOTLB_INIT_REMAP		(1 << 3)
+#define SWIOTLB_INIT_REMAP		(1 << 2)
  /* Do not initialize a pool unless SWIOTLB is explicitly required. */
-#define SWIOTLB_INIT_DEFAULT_OFF		(1 << 4)
+#define SWIOTLB_INIT_DEFAULT_OFF	(1 << 3)
  
  /*
   * Maximum allowable number of contiguous slabs to map,

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 46b789eb0806..77d7c320de28 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c

@@ -450,15 +450,10 @@ static void __init *swiotlb_memblock_alloc(unsigned long nslabs,
  	size_t bytes = PAGE_ALIGN(nslabs << IO_TLB_SHIFT);
  	void *tlb;
  
-	/*
-	 * By default allocate the bounce buffer memory from low memory, but
-	 * allow to pick a location everywhere for hypervisors with guest
-	 * memory encryption.
-	 */
-	if (flags & SWIOTLB_ANY)
-		tlb = memblock_alloc(bytes, PAGE_SIZE);
-	else
+	if (flags & SWIOTLB_INIT_ADDRESSING_LIMIT)
  		tlb = memblock_alloc_low(bytes, PAGE_SIZE);
+	else
+		tlb = memblock_alloc(bytes, PAGE_SIZE);
  
  	if (!tlb) {
  		pr_warn("%s: Failed to allocate %zu bytes tlb structure\n",

@@ -604,10 +599,10 @@ void __init swiotlb_init_remap(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
+	if (flags & SWIOTLB_INIT_ADDRESSING_LIMIT)
  		io_tlb_default_mem.phys_limit = ARCH_LOW_ADDRESS_LIMIT;
+	else
+		io_tlb_default_mem.phys_limit = virt_to_phys(high_memory - 1);
  #endif
  
  	/* if we have host or guest memory encryption */