From 22d0213e55fbb723c2c00dd5aa855a6eaad95b23 Mon Sep 17 00:00:00 2001 From: Petr Tesarik Date: Fri, 10 Apr 2026 13:35:06 +0200 Subject: [PATCH] dma-direct: fix use of max_pfn Calculate the correct physical address of the last byte of memory. Since max_pfn is in fact "the PFN of the first page after the highest system RAM in physical address space", the highest address that might be used for a DMA buffer is one byte below max_pfn << PAGE_SHIFT. This fix is unlikely to make any difference in practice. It's just that the current formula is slightly confusing. Signed-off-by: Petr Tesarik Signed-off-by: Marek Szyprowski Link: https://lore.kernel.org/r/20260410113506.262579-1-ptesarik@suse.com --- kernel/dma/direct.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c index ec887f443741..583c5922bca2 100644 --- a/kernel/dma/direct.c +++ b/kernel/dma/direct.c @@ -39,7 +39,7 @@ static inline struct page *dma_direct_to_page(struct device *dev, u64 dma_direct_get_required_mask(struct device *dev) { - phys_addr_t phys = (phys_addr_t)(max_pfn - 1) << PAGE_SHIFT; + phys_addr_t phys = ((phys_addr_t)max_pfn << PAGE_SHIFT) - 1; u64 max_dma = phys_to_dma_direct(dev, phys); return (1ULL << (fls64(max_dma) - 1)) * 2 - 1; @@ -553,7 +553,7 @@ int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma, int dma_direct_supported(struct device *dev, u64 mask) { - u64 min_mask = (max_pfn - 1) << PAGE_SHIFT; + u64 min_mask = ((u64)max_pfn << PAGE_SHIFT) - 1; /* * Because 32-bit DMA masks are so common we expect every architecture