On Mon, Dec 15, 2014 at 04:35:12PM +0000, Varun Sethi wrote: > -----Original Message----- > From: Will Deacon [mailto:will.dea...@arm.com] > Sent: Monday, December 15, 2014 9:13 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 Mon, Dec 15, 2014 at 01:30:20PM +0000, Will Deacon wrote: > > On Sun, Dec 14, 2014 at 05:45:49PM +0000, Varun Sethi wrote: > > > [varun] ok, but you could potentially end up splitting mapping to > > > the least possible page size e.g. 4K. You, don't seem to take in to > > > account the possibility of using the block size at the next level. > > > For example, take a case where we have a huge page mapping using 1G > > > page size and we have an unmap request for 4K. We could still split > > > maximum part of the mapping using 2M pages at the next level. The > > > entry where we need to unmap the 4K region would potentially go to the > > > next level. > > > > Aha, I see what you mean here, thanks. I'll take a look... > > Scratch that, I think the code is fine as it is. For the case you > highlight, we iterate over the 1GB region remapping it using 4k pages, but > skipping the one we want to unmap, so I don't think there's a problem > (__arm_lpae_map will create the relevant table entries). > > > [[varun]] But you can split 1G in 2M mappings and then split up the > unmapped region using 4K pages. In this case you split up the entire > region using 4K pages.
True, I miss an optimisation opportunity there, but I don't know that it's common enough to care (in the same way that we don't recreate a 1G mapping if you remapped that 4k page back like it was). You could add this by making arm_lpae_split_blk_unmap recursive, if you wanted to. Will _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
