On Tue, Mar 30, 2021 at 05:28:19PM +0100, Robin Murphy wrote: > On 2021-03-30 14:58, Will Deacon wrote: > > On Tue, Mar 30, 2021 at 02:19:38PM +0100, Robin Murphy wrote: > > > On 2021-03-30 14:11, Will Deacon wrote: > > > > On Tue, Mar 16, 2021 at 04:38:22PM +0100, Christoph Hellwig wrote: > > > > > From: Robin Murphy <robin.murphy@xxxxxxx> > > > > > > > > > > Instead make the global iommu_dma_strict paramete in iommu.c canonical by > > > > > exporting helpers to get and set it and use those directly in the drivers. > > > > > > > > > > This make sure that the iommu.strict parameter also works for the AMD and > > > > > Intel IOMMU drivers on x86. As those default to lazy flushing a new > > > > > IOMMU_CMD_LINE_STRICT is used to turn the value into a tristate to > > > > > represent the default if not overriden by an explicit parameter. > > > > > > > > > > Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>. > > > > > [ported on top of the other iommu_attr changes and added a few small > > > > > missing bits] > > > > > Signed-off-by: Christoph Hellwig <hch@xxxxxx> > > > > > --- > > > > > drivers/iommu/amd/iommu.c | 23 +------- > > > > > drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 50 +--------------- > > > > > drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 1 - > > > > > drivers/iommu/arm/arm-smmu/arm-smmu.c | 27 +-------- > > > > > drivers/iommu/dma-iommu.c | 9 +-- > > > > > drivers/iommu/intel/iommu.c | 64 ++++----------------- > > > > > drivers/iommu/iommu.c | 27 ++++++--- > > > > > include/linux/iommu.h | 4 +- > > > > > 8 files changed, 40 insertions(+), 165 deletions(-) > > > > > > > > I really like this cleanup, but I can't help wonder if it's going in the > > > > wrong direction. With SoCs often having multiple IOMMU instances and a > > > > distinction between "trusted" and "untrusted" devices, then having the > > > > flush-queue enabled on a per-IOMMU or per-domain basis doesn't sound > > > > unreasonable to me, but this change makes it a global property. > > > > > > The intent here was just to streamline the existing behaviour of stuffing a > > > global property into a domain attribute then pulling it out again in the > > > illusion that it was in any way per-domain. We're still checking > > > dev_is_untrusted() before making an actual decision, and it's not like we > > > can't add more factors at that point if we want to. > > > > Like I say, the cleanup is great. I'm just wondering whether there's a > > better way to express the complicated logic to decide whether or not to use > > the flush queue than what we end up with: > > > > if (!cookie->fq_domain && (!dev || !dev_is_untrusted(dev)) && > > domain->ops->flush_iotlb_all && !iommu_get_dma_strict()) > > > > which is mixing up globals, device properties and domain properties. The > > result is that the driver code ends up just using the global to determine > > whether or not to pass IO_PGTABLE_QUIRK_NON_STRICT to the page-table code, > > which is a departure from the current way of doing things. > > But previously, SMMU only ever saw the global policy piped through the > domain attribute by iommu_group_alloc_default_domain(), so there's no > functional change there. For DMA domains sure, but I don't think that's the case for unmanaged domains such as those used by VFIO. > Obviously some of the above checks could be factored out into some kind of > iommu_use_flush_queue() helper that IOMMU drivers can also call if they need > to keep in sync. Or maybe we just allow iommu-dma to set > IO_PGTABLE_QUIRK_NON_STRICT directly via iommu_set_pgtable_quirks() if we're > treating that as a generic thing now. I think a helper that takes a domain would be a good starting point. Will
