RE: [PATCH 1/1] mm: Fix struct page layout on 32-bit systems

[David Laight <David.Laight@ACULAB.COM>]

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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