Commit e9696d25 authored Oct 26, 2020 by Stefano Stabellini Committed by Konrad Rzeszutek Wilk Nov 02, 2020

swiotlb: fix "x86: Don't panic if can not alloc buffer for swiotlb"



kernel/dma/swiotlb.c:swiotlb_init gets called first and tries to
allocate a buffer for the swiotlb. It does so by calling

  memblock_alloc_low(PAGE_ALIGN(bytes), PAGE_SIZE);

If the allocation must fail, no_iotlb_memory is set.

Later during initialization swiotlb-xen comes in
(drivers/xen/swiotlb-xen.c:xen_swiotlb_init) and given that io_tlb_start
is != 0, it thinks the memory is ready to use when actually it is not.

When the swiotlb is actually needed, swiotlb_tbl_map_single gets called
and since no_iotlb_memory is set the kernel panics.

Instead, if swiotlb-xen.c:xen_swiotlb_init knew the swiotlb hadn't been
initialized, it would do the initialization itself, which might still
succeed.

Fix the panic by setting io_tlb_start to 0 on swiotlb initialization
failure, and also by setting no_iotlb_memory to false on swiotlb
initialization success.

Fixes: ac2cbab2 ("x86: Don't panic if can not alloc buffer for swiotlb")

Reported-by: Elliott Mitchell <ehem+xen@m5p.com>
Tested-by: Elliott Mitchell <ehem+xen@m5p.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

parent 3650b228

kernel/dma/swiotlb.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -229,6 +229,7 @@ int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
		io_tlb_orig_addr[i] = INVALID_PHYS_ADDR;
		}
		io_tlb_index = 0;
		no_iotlb_memory = false;

		if (verbose)
		swiotlb_print_info();
		@@ -260,9 +261,11 @@ swiotlb_init(int verbose)
		if (vstart && !swiotlb_init_with_tbl(vstart, io_tlb_nslabs, verbose))
		return;

		if (io_tlb_start)
		if (io_tlb_start) {
		memblock_free_early(io_tlb_start,
		PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT));
		io_tlb_start = 0;
		}
		pr_warn("Cannot allocate buffer");
		no_iotlb_memory = true;
		}
		@@ -360,6 +363,7 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
		io_tlb_orig_addr[i] = INVALID_PHYS_ADDR;
		}
		io_tlb_index = 0;
		no_iotlb_memory = false;

		swiotlb_print_info();

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