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SubjectRE: [PATCH 1/1] mm: Fix struct page layout on 32-bit systems
Date
From: Matthew Wilcox
> Sent: 16 April 2021 16:28
>
> On Thu, Apr 15, 2021 at 08:08:32PM +0200, Jesper Dangaard Brouer wrote:
> > See below patch. Where I swap32 the dma address to satisfy
> > page->compound having bit zero cleared. (It is the simplest fix I could
> > come up with).
>
> I think this is slightly simpler, and as a bonus code that assumes the
> old layout won't compile.

Always a good plan.

...
> static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
> {
> - return page->dma_addr;
> + dma_addr_t ret = page->dma_addr[0];
> + if (sizeof(dma_addr_t) > sizeof(unsigned long))
> + ret |= (dma_addr_t)page->dma_addr[1] << 32;
> + return ret;
> +}

Won't some compiler/option combinations generate an
error for the '<< 32' when dma_addr_t is 32bit?

You might need to use a (u64) cast.

David

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