This is a note to let you know that I've just added the patch titled swiotlb: fix "x86: Don't panic if can not alloc buffer for swiotlb" to the 5.9-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-fix-x86-don-t-panic-if-can-not-alloc-buffer-for-swiotlb.patch and it can be found in the queue-5.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From e9696d259d0fb5d239e8c28ca41089838ea76d13 Mon Sep 17 00:00:00 2001 From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx> Date: Mon, 26 Oct 2020 17:02:14 -0700 Subject: swiotlb: fix "x86: Don't panic if can not alloc buffer for swiotlb" From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx> commit e9696d259d0fb5d239e8c28ca41089838ea76d13 upstream. 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: ac2cbab21f31 ("x86: Don't panic if can not alloc buffer for swiotlb") Reported-by: Elliott Mitchell <ehem+xen@xxxxxxx> Tested-by: Elliott Mitchell <ehem+xen@xxxxxxx> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/dma/swiotlb.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -231,6 +231,7 @@ int __init swiotlb_init_with_tbl(char *t io_tlb_orig_addr[i] = INVALID_PHYS_ADDR; } io_tlb_index = 0; + no_iotlb_memory = false; if (verbose) swiotlb_print_info(); @@ -262,9 +263,11 @@ 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; } @@ -362,6 +365,7 @@ swiotlb_late_init_with_tbl(char *tlb, un io_tlb_orig_addr[i] = INVALID_PHYS_ADDR; } io_tlb_index = 0; + no_iotlb_memory = false; swiotlb_print_info(); Patches currently in stable-queue which might be from stefano.stabellini@xxxxxxxxxx are queue-5.9/swiotlb-fix-x86-don-t-panic-if-can-not-alloc-buffer-for-swiotlb.patch