From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH 2/4] iommu: add ARM LPAE page table allocator Date: Mon, 15 Dec 2014 17:20:40 +0000 Message-ID: <20141215172040.GQ20738@arm.com> References: <1417089078-22900-1-git-send-email-will.deacon@arm.com> <1417089078-22900-3-git-send-email-will.deacon@arm.com> <20141205184802.GH1203@arm.com> <20141215133020.GJ20738@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Varun Sethi Cc: "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "laurent.pinchart-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org" , "prem.mallappa-dY08KVG/lbpWk0Htik3J/w@public.gmane.org" , Robin Murphy , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" List-Id: iommu@lists.linux-foundation.org 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. Will