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 <robin.mur...@arm.com> > > > > > > > > > > --- > > > > > > > > > > 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 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
