[PATCH 2/4] iommu: add ARM LPAE page table allocator
will.deacon at arm.com
Mon Dec 15 09:20:40 PST 2014
On Mon, Dec 15, 2014 at 04:43:59PM +0000, Varun Sethi wrote:
> > Sure we can support 48-bit VAs with 64k pages. Why do you think we can't?
> > [varun] My concern was with respect to the bits per level, which is
> > uneven for the 64 K page sizes. Just wondering how would things work
> > with 64K pages when we do a 3 level page lookup.
> Well, it's uneven (9) for the 4k case too. Do you actually see an issue here?
> 48-bit VA with 64k pages gives us:
> va_bits = (48 - 16) = 32
> bits_per_level = (16 - 3) = 13
> levels = ceil(32/13) = 3
> so the starting level is 1, which resolves 32-(13*2) = 6 bits.
> Does that make sense?
> [[varun]]Yes, but what I meant was, is that in case of 4K pages you have 9
> bits per level, but for 64K pages you have 6 bits for the first level and
> 13 each for second and third. So, bits per level would not work in case of
> 64 K pages?
The current code takes this into account.
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