linux-kernel - Is iommu_num

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Date:	Sun, 05 Aug 2012 10:16:56 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Joerg Roedel <joerg.roedel@....com>
Cc:	Anton Blanchard <anton@....ibm.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	linux-kernel@...r.kernel.org
Subject: Is iommu_num_pages() broken ?

Hi folks !

I stumbled upon this today:

static inline unsigned long iommu_num_pages(unsigned long addr,
					    unsigned long len,
					    unsigned long io_page_size)
{
	unsigned long size = (addr & (io_page_size - 1)) + len;

	return DIV_ROUND_UP(size, io_page_size);
}
 

That doesn't look right to me...

The powerpc iommu code at least uses that with an addr which may not be
page aligned (ie, result of sg_virt() which include the offset).

The above code will align the start before adding the len which is wrong
and will result in potentially missing a page or am I missing
something ?

Shouldn't it be something like

static inline unsigned long iommu_num_pages(unsigned long addr,
					    unsigned long len,
					    unsigned long io_page_size)
{
	unsigned long start = addr & (io_page_size - 1);
	unsigned long end = addr + len;

	return DIV_ROUND_UP(end - start, io_page_size);
}

?

Cheers,
Ben.


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