Patch "swiotlb: reduce the swiotlb buffer size on allocation failure" has been added to the 6.1-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    swiotlb: reduce the swiotlb buffer size on allocation failure

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     swiotlb-reduce-the-swiotlb-buffer-size-on-allocation.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit fa5816c6a9d111dad466bebe4c8d8f115019c375
Author: Alexey Kardashevskiy <aik@xxxxxxx>
Date:   Mon Oct 31 19:13:27 2022 +1100

    swiotlb: reduce the swiotlb buffer size on allocation failure
    
    [ Upstream commit 8d58aa484920c4f9be4834a7aeb446cdced21a37 ]
    
    At the moment the AMD encrypted platform reserves 6% of RAM for SWIOTLB
    or 1GB, whichever is less. However it is possible that there is no block
    big enough in the low memory which make SWIOTLB allocation fail and
    the kernel continues without DMA. In such case a VM hangs on DMA.
    
    This moves alloc+remap to a helper and calls it from a loop where
    the size is halved on each iteration.
    
    This updates default_nslabs on successful allocation which looks like
    an oversight as not doing so should have broken callers of
    swiotlb_size_or_default().
    
    Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxx>
    Reviewed-by: Pankaj Gupta <pankaj.gupta@xxxxxxx>
    Signed-off-by: Christoph Hellwig <hch@xxxxxx>
    Stable-dep-of: 8ac04063354a ("swiotlb: reduce the number of areas to match actual memory pool size")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 3961065412542..cc0c55ed20429 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -307,6 +307,37 @@ static void swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,
 	return;
 }
 
+static void *swiotlb_memblock_alloc(unsigned long nslabs, unsigned int flags,
+		int (*remap)(void *tlb, 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
+		tlb = memblock_alloc_low(bytes, PAGE_SIZE);
+
+	if (!tlb) {
+		pr_warn("%s: Failed to allocate %zu bytes tlb structure\n",
+			__func__, bytes);
+		return NULL;
+	}
+
+	if (remap && remap(tlb, nslabs) < 0) {
+		memblock_free(tlb, PAGE_ALIGN(bytes));
+		pr_warn("%s: Failed to remap %zu bytes\n", __func__, bytes);
+		return NULL;
+	}
+
+	return tlb;
+}
+
 /*
  * Statically reserve bounce buffer space and initialize bounce buffer data
  * structures for the software IO TLB used to implement the DMA API.
@@ -317,7 +348,6 @@ void __init swiotlb_init_remap(bool addressing_limit, unsigned int flags,
 	struct io_tlb_mem *mem = &io_tlb_default_mem;
 	unsigned long nslabs;
 	size_t alloc_size;
-	size_t bytes;
 	void *tlb;
 
 	if (!addressing_limit && !swiotlb_force_bounce)
@@ -329,31 +359,16 @@ void __init swiotlb_init_remap(bool addressing_limit, unsigned int flags,
 		swiotlb_adjust_nareas(num_possible_cpus());
 
 	nslabs = default_nslabs;
-	/*
-	 * By default allocate the bounce buffer memory from low memory, but
-	 * allow to pick a location everywhere for hypervisors with guest
-	 * memory encryption.
-	 */
-retry:
-	bytes = PAGE_ALIGN(nslabs << IO_TLB_SHIFT);
-	if (flags & SWIOTLB_ANY)
-		tlb = memblock_alloc(bytes, PAGE_SIZE);
-	else
-		tlb = memblock_alloc_low(bytes, PAGE_SIZE);
-	if (!tlb) {
-		pr_warn("%s: failed to allocate tlb structure\n", __func__);
-		return;
-	}
-
-	if (remap && remap(tlb, nslabs) < 0) {
-		memblock_free(tlb, PAGE_ALIGN(bytes));
-
+	while ((tlb = swiotlb_memblock_alloc(nslabs, flags, remap)) == NULL) {
+		if (nslabs <= IO_TLB_MIN_SLABS)
+			return;
 		nslabs = ALIGN(nslabs >> 1, IO_TLB_SEGSIZE);
-		if (nslabs >= IO_TLB_MIN_SLABS)
-			goto retry;
+	}
 
-		pr_warn("%s: Failed to remap %zu bytes\n", __func__, bytes);
-		return;
+	if (default_nslabs != nslabs) {
+		pr_info("SWIOTLB bounce buffer size adjusted %lu -> %lu slabs",
+			default_nslabs, nslabs);
+		default_nslabs = nslabs;
 	}
 
 	alloc_size = PAGE_ALIGN(array_size(sizeof(*mem->slots), nslabs));