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 <[email protected]> > >>>>>>--- > >>>>>> 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. Let me know if you need any help. I've got a little time and more than a little motivation to keep slogging ahead toward a glorious arm-smmu-v2 per-context pagetable future. Jordan -- The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
