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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1iNbTj-0007TK-AV; Thu, 24 Oct 2019 11:40:31 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1iNbTg-0007SG-Aj for linux-arm-kernel@lists.infradead.org; Thu, 24 Oct 2019 11:40:30 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E88FA20679; Thu, 24 Oct 2019 11:40:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571917227; bh=+5fAWXg25kh+vAkL7o5Ici9Ua+HaM74bc25Pav0jXqQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=1dhg8R4zpzAi631XaKnTUPCNGgsuKBT7TQ9X3uiJPcF4sctDfQPCLCeIuWQoi/sdY u9NP7bCmBNR5eRn/rPhg6YGF+a2d2maBHYj0oak5UODbjrps63f9BEf/FgUN2dVbdf g2ub9w6HKV0/NjmlSYXzKAmrTARIKCJw+0tHUF+M= Date: Thu, 24 Oct 2019 12:40:22 +0100 From: Will Deacon To: Robin Murphy Subject: Re: [PATCH 3/4] iommu/io-pgtable-arm: Rationalise TCR handling Message-ID: <20191024114022.GE1242@willie-the-truck> References: <78df4f8e2510e88f3ded59eb385f79b4442ed4f2.1566238530.git.robin.murphy@arm.com> <20190820103115.o7neehdethf7sbqi@willie-the-truck> <48ca6945-de73-116a-3230-84862ca9e60b@arm.com> <20190820160700.6ircxomwuo5bksqz@willie-the-truck> <8cc47f43-ad74-b4e2-e977-6c78780abc91@arm.com> <20190821121120.34wqo7vj56pqk57c@willie-the-truck> <20191003173352.GA13386@jcrouse1-lnx.qualcomm.com> <20191024105111.GB1242@willie-the-truck> <63fa5848-372d-fe09-7502-1b9ecbcc6cf0@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <63fa5848-372d-fe09-7502-1b9ecbcc6cf0@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191024_044028_413961_0F59321B X-CRM114-Status: GOOD ( 33.62 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: robdclark@gmail.com, joro@8bytes.org, iommu@lists.linux-foundation.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Oct 24, 2019 at 12:23:46PM +0100, Robin Murphy wrote: > On 2019-10-24 11:51 am, Will Deacon wrote: > > On Thu, Oct 03, 2019 at 11:33:52AM -0600, Jordan Crouse wrote: > > > On Wed, Aug 21, 2019 at 01:56:20PM +0100, Robin Murphy wrote: > > > > On 21/08/2019 13:11, Will Deacon wrote: > > > > > On Tue, Aug 20, 2019 at 07:41:52PM +0100, Robin Murphy wrote: > > > > > > On 20/08/2019 17:07, Will Deacon wrote: > > > > > > > On Tue, Aug 20, 2019 at 04:25:56PM +0100, Robin Murphy wrote: > > > > > > > > On 20/08/2019 11:31, Will Deacon wrote: > > > > > > > > > On Mon, Aug 19, 2019 at 07:19:30PM +0100, Robin Murphy wrote: > > > > > > > > > > Although it's conceptually nice for the io_pgtable_cfg to provide a > > > > > > > > > > standard VMSA TCR value, the reality is that no VMSA-compliant IOMMU > > > > > > > > > > looks exactly like an Arm CPU, and they all have various other TCR > > > > > > > > > > controls which io-pgtable can't be expected to understand. Thus since > > > > > > > > > > there is an expectation that drivers will have to add to the given TCR > > > > > > > > > > value anyway, let's strip it down to just the essentials that are > > > > > > > > > > directly relevant to io-pgatble's inner workings - namely the address > > > > > > > > > > sizes, walk attributes, and where appropriate, format selection. > > > > > > > > > > > > > > > > > > > > Signed-off-by: Robin Murphy > > > > > > > > > > --- > > > > > > > > > > drivers/iommu/arm-smmu-v3.c | 7 +------ > > > > > > > > > > drivers/iommu/arm-smmu.c | 1 + > > > > > > > > > > drivers/iommu/arm-smmu.h | 2 ++ > > > > > > > > > > drivers/iommu/io-pgtable-arm-v7s.c | 6 ++---- > > > > > > > > > > drivers/iommu/io-pgtable-arm.c | 4 ---- > > > > > > > > > > drivers/iommu/qcom_iommu.c | 2 +- > > > > > > > > > > 6 files changed, 7 insertions(+), 15 deletions(-) > > > > > > > > > > > > > > > > > > Hmm, so I'm a bit nervous about this one since I think we really should > > > > > > > > > be providing a TCR with EPD1 set if we're only giving you TTBR0. Relying > > > > > > > > > on the driver to do this worries me. See my comments on the next patch. > > > > > > > > > > > > > > > > The whole idea is that we already know we can't provide a *complete* TCR > > > > > > > > value (not least because anything above bit 31 is the wild west), thus > > > > > > > > there's really no point in io-pgtable trying to provide anything other than > > > > > > > > the parts it definitely controls. It makes sense to provide this partial TCR > > > > > > > > value "as if" for TTBR0, since that's the most common case, but ultimately > > > > > > > > io-pgatble doesn't know (or need to) which TTBR the caller intends to > > > > > > > > actually use for this table. Even if the caller *is* allocating it for > > > > > > > > TTBR0, io-pgtable doesn't know that they haven't got something live in TTBR1 > > > > > > > > already, so it still wouldn't be in a position to make the EPD1 call either > > > > > > > > way. > > > > > > > > > > > > > > Ok, but the driver can happily rewrite/ignore what it gets back. I suppose > > > > > > > an alternative would be scrapped the 'u64 tcr' and instead having a bunch > > > > > > > of named bitfields for the stuff we're actually providing, although I'd > > > > > > > still like EPDx to be in there. > > > > > > > > > > > > I like the bitfield idea; it would certainly emphasise the "you have to do > > > > > > something more with this" angle that I'm pushing towards here, but still > > > > > > leave things framed in TCR terms without having to go to some more general > > > > > > abstraction. It really doesn't play into your EPD argument though - such a > > > > > > config would be providing TxSZ/TGx/IRGNx/ORGNx/SHx, but EPDy, for y = !x. > > > > > > For a driver to understand that and do the right thing with it is even more > > > > > > involved than for the driver to just set EPD1 by itself anyway. > > > > > > > > > > Having considered the bitfield idea some more, I'm less attached to EPDx > > > > > because we simply wouldn't be making a statement about them, rather than a > > > > > (dangerous) zero value and expecting it to be ignored. So I think we're in > > > > > agreement on that. > > > > > > > > Cool, I'll give bitfields a go for v2. > > > > > > > > > The only part I'm still stuck to is that I think io-pgtable should know > > > > > whether it's targetting TTBR0 or TTBR1 so that it can sanitise input > > > > > addresses correctly. Doing this in the driver code is possible, but I'd > > > > > rather not start from that position, particularly as it would require things > > > > > like sign-extension in the TLBI callbacks. > > > > > > Bumping this as is our tradition in the -rc1 time frame before we get all > > > distracted with other stuff. It sounds like the last agreement was for a > > > TTBR1 hint for the EDP and the sign extension in the functions. > > > > If somebody respins this using bitfields and an explicit TTBR1 quirk then > > I'll merge it. > > Oops, the ping did register, I just didn't react outwardly ;) > > I have been working on v2, and plan to have something ready next week - the > holdup was that I started refactoring all the argument passing since the > number of things we have to carry through from one end of map/unmap to the > other is getting a bit silly, but I think I can still finish the TTBR1 quirk > without that, so if I don't get it cracked imminently then I'll put it aside > to revisit later. Cheers, Robin! I'll keep an eye out for it. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel