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dma-direct: fix use of max_pfn

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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 <ptesarik@suse.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20260410113506.262579-1-ptesarik@suse.com
This commit is contained in:
Petr Tesarik 2026-04-10 13:35:06 +02:00 committed by Marek Szyprowski
parent 254f49634e
commit 22d0213e55
1 changed files with 2 additions and 2 deletions
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4
kernel/dma/direct.c
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@ -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