7.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Marek Szyprowski commit 911655ab1dfb9d526978a75df3b210132620d30a upstream. Commit ad96ce3252db ("swiotlb: determine potential physical address limit") changed default_swiotlb_limit() to return the maximum physical address that could ever be used by dynamically allocated pools, so that the value stays constant when CONFIG_SWIOTLB_DYNAMIC=y. However, io_tlb_default_mem.phys_limit is returned even when the default pool cannot grow, e.g. when swiotlb_init_remap() is called with a remap callback. This breaks Xen dom0 on x86: pci_xen_swiotlb_init() passes SWIOTLB_ANY and xen_swiotlb_fixup(), so phys_limit is set to the top of dom0 memory, although xen_swiotlb_fixup() makes the default pool below the 32-bit boundary. xen_swiotlb_dma_supported() then rejects 32-bit DMA masks, even though the bounce buffer is perfectly usable by such devices. Return phys_limit only if the default pool can actually grow, otherwise report the real end of the default pool, like in the !CONFIG_SWIOTLB_DYNAMIC case. Reported-by: Andreas Greve Reported-by: James Dingwall Fixes: ad96ce3252db ("swiotlb: determine potential physical address limit") Closes: https://lore.kernel.org/xen-devel/f74668db-52fd-4575-8372-7bfdf10d62ac@a-greve.de/ Cc: stable@vger.kernel.org Assisted-by: Claude Opus 5.5 (1M context) Tested-by: James Dingwall Link: https://lore.kernel.org/all/20261005070518.1590097-1-m.szyprowski@samsung.com/ Signed-off-by: Marek Szyprowski Signed-off-by: Greg Kroah-Hartman --- kernel/dma/swiotlb.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -1680,10 +1680,10 @@ 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; + if (io_tlb_default_mem.can_grow) + return io_tlb_default_mem.phys_limit; #endif + return io_tlb_default_mem.defpool.end - 1; } #ifdef CONFIG_DEBUG_FS