From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 765DD367B7E; Wed, 22 Jul 2026 21:42:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784756563; cv=none; b=RAsqBjEy5ApsLA52bhwoEyiWevOWp/3V2aka/Kw3pEFqG8jmJ29yLlutcYeHKIQVXQgIeTvU9/QcsMIv4xPPK2jW2PiwLYxGrJpCZnZ42fDj4DJ8l4dzn8pLRhk/7NAODu6rP4BqtfxxGD1ZbR0W/INGYsCg6ItKPclkTaj6+CE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784756563; c=relaxed/simple; bh=LWEs48QXpuNXuL4poANcBKLLN+cPyhQFQENq70XY1y8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QcpyDT3J8TEAy6MyPj86Itc2x9VQgN4zUpYWr109LbFGRh8SG3pCbIhSqJlx7uhcoxkm3cgFuIpyN5F1xDsORwg01P7wMaZBTjJrzw/hyg+4K1p+oGIvPyfvwnmmLE+HfaphtaEcnYUm8U8q1uQuTMRkisJ7DSREcv46uBehdC4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fPEv5Xfy; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="fPEv5Xfy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9076A1F000E9; Wed, 22 Jul 2026 21:42:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784756562; bh=ed4T4xJjlrAZXH7SdCvLneLF0/yxPPXnPkh3K7AaOfQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=fPEv5XfyolxPMevnNfBaZ2im8pSAn8nujZnXszBTCkjPI/wA4aVny7vmXgl5FpNLk 2irJA1dPwd6QC+Yy913E/1FGFUdUIo5FxZWlojrG0O9nkIJQ4DqIqylbaaxPnNzqe0 RpXOrSb/Mttb55HnoMZblGXLGTpU5vbryBFw06bhlM4bgNe9rKDNEWSaIz7yijbljV vTstFZl6fOw9fIOFUaHx1w5JTBWBhEtnOSZNKYCDy78t8JsfFKiMpfcoEHkwfBqqn/ l89ugTCLvx+Km3cADcP9eB5XBUJm2cmYU2OnU+xtGDgmOo7Pc98eVWgm4/MQW/EikI r8H5/c514C2Zw== Date: Wed, 22 Jul 2026 22:42:37 +0100 From: Will Deacon To: Robin Murphy Cc: Jason Gunthorpe , Vijayanand Jitta , "Joerg Roedel (AMD)" , linux-arm-msm@vger.kernel.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Prakash Gupta Subject: Re: [PATCH] iommu/io-pgtable-arm: Add support for contiguous hint bit Message-ID: References: <20260618-iommu_contig_hint-v1-1-4502a59e6388@oss.qualcomm.com> <20260703161228.GA1948451@nvidia.com> <20260715113913.GA3775915@nvidia.com> <2ce09e84-c57f-4087-9dda-07245fadfc02@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2ce09e84-c57f-4087-9dda-07245fadfc02@arm.com> On Wed, Jul 15, 2026 at 01:14:18PM +0100, Robin Murphy wrote: > On 15/07/2026 1:03 pm, Will Deacon wrote: > > On Wed, Jul 15, 2026 at 08:39:13AM -0300, Jason Gunthorpe wrote: > > > On Wed, Jul 15, 2026 at 11:25:42AM +0530, Vijayanand Jitta wrote: > > > > On 7/3/2026 9:42 PM, Jason Gunthorpe wrote: > > > > > On Thu, Jun 18, 2026 at 02:32:09PM +0530, Vijayanand Jitta wrote: > > > > > > From: Prakash Gupta > > > > > > > > > > > > Add support for the contiguous hint (CONT) bit in ARM LPAE page tables. > > > > > > When a set of consecutive PTEs map a naturally-aligned contiguous block > > > > > > of memory, the CONT bit can be set on all entries in the group to allow > > > > > > the hardware to combine them into a single TLB entry, improving TLB > > > > > > utilization. > > > > > > > > > > > > The contiguous hint sizes per granule are: > > > > > > > > > > > > Page Size | CONT PTE | PMD | CONT PMD > > > > > > ----------+----------+-------+--------- > > > > > > 4K | 64K | 2M | 32M > > > > > > 16K | 2M | 32M | 1G > > > > > > 64K | 2M | 512M | 16G > > > > > > > > > > My series to convert smmuv3 to the iommupt takes care of this and > > > > > supports all the orders too. I'd rather we move forward with that then > > > > > try to patch up this. > > > > > > > > Thanks for details, I have gone through your series. As this patch > > > > targets io-pgtable-arm.c directly and would benefit all its users (SMMUv2, > > > > Apple DART, etc.), not just SMMUv3. I think there will still be value in > > > > this patch for the other users. > > > > > > If other users care they should also be converted to iommupt, there > > > are many benefits to this besides just cont support. > > > > I really have no interest in maintaining two copies of the page-table > > code, so I agree that we should convert users of the architectural (long > > descriptor) page-table format over to iommupt with a view to removing > > the io-pgtable implementation eventually. If you want two parallel > > implementations, then one should really be in rust :) > > > > From what I can tell, the fiddly parts for iommupt will be: > > > > 1. Hardware bugs / quirks. Some of the simpler ones could probably be > > handled but for the more invasive stuff like the Mali format > > format, io-pgtable will probably need to hang around. Perhaps > > it becomes io-pgtable-mali.c? > > > > 2. The pKVM work from Mostafa. We'll probably end up with something > > separate at EL2 for this (ideally, just reusing the CPU page-table > > code when it learns about BBML3). > > > > 3. Non-coherent walkers, although I think this might actually be fine > > because x86 needs it anyway? > > > > So, for now, I wouldn't require new drivers to use iommupt but I'm not > > particularly keen about teaching io-pgtable new architectural tricks > > either. > > Conversely though, I really wouldn't want to have to maintain arm-smmu > supporting two completely different pagetable APIs simultaneously either :/ Yeah, we'll have to see how it pans out. I suppose the first step is for somebody to go through Jason's iommupt series for SMMUv3 and get that driver converted. Once we've got that working, we should have a better idea about what to do with arm-smmu. If we can't get to a point where drivers are no longer using the long descriptor io-pgtable implementation, then we'll obviously not get rid of it, but I think it will become "fixes only" or something like that. Will