-----Original Message----- From: Will Deacon [mailto:will.dea...@arm.com] Sent: Monday, December 15, 2014 7:00 PM To: Sethi Varun-B16395 Cc: linux-arm-ker...@lists.infradead.org; iommu@lists.linux-foundation.org; prem.malla...@broadcom.com; Robin Murphy; lau...@codeaurora.org; mitch...@codeaurora.org; laurent.pinch...@ideasonboard.com; j...@8bytes.org; m.szyprow...@samsung.com Subject: Re: [PATCH 2/4] iommu: add ARM LPAE page table allocator
On Sun, Dec 14, 2014 at 05:45:49PM +0000, Varun Sethi wrote: > Please find my response inline. Search for "varun". This is getting fiddly now that you've already replied once. Any chance you could sort your mail client out, please? [[varun]] Yes I need to do that, this is painful. > > + if (!data) > > + return NULL; > > + > > + data->pages_per_pgd = 1; > > + data->pg_shift = __ffs(cfg->pgsize_bitmap); > > + data->bits_per_level = data->pg_shift - > > + ilog2(sizeof(arm_lpae_iopte)); > > + > > + va_bits = cfg->ias - data->pg_shift; > > + data->levels = DIV_ROUND_UP(va_bits, data->bits_per_level); > > > > [[varun]] Not related to the patch, but this would be applicable to > > the CPU tables as well i.e, we can't support 48bit VA with 64 KB > > page tables, right? The AR64 memory maps shows possibility of using > > 6 bits for the first level page table. > > 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? Thanks, Varun _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
