Messages in this thread Patch in this message | | | Date | Wed, 5 Oct 2022 10:53:50 +0100 | Subject | Re: [PATCH v4 5/5] iommu/s390: Fix incorrect pgsize_bitmap | From | Robin Murphy <> |
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On 2022-10-04 17:13, Niklas Schnelle wrote: > On Tue, 2022-10-04 at 16:31 +0100, Robin Murphy wrote: >> On 2022-10-04 16:12, Matthew Rosato wrote: >>> On 10/4/22 11:02 AM, Robin Murphy wrote: >>>> On 2022-10-04 13:07, Niklas Schnelle wrote: >>>>> The .pgsize_bitmap property of struct iommu_ops is not a page mask but >>>>> rather has a bit set for each size of pages the IOMMU supports. As the >>>>> comment correctly pointed out at this moment the code only support 4K >>>>> pages so simply use SZ_4K here. >>>> >>>> Unless it's already been done somewhere else, you'll want to switch over to the {map,unmap}_pages() interfaces as well to avoid taking a hit on efficiency here. The "page mask" thing was an old hack to trick the core API into making fewer map/unmap calls where the driver could map arbitrary numbers of pages at once anyway. The multi-page interfaces now do that more honestly and generally better (since they work for non-power-of-two sizes as well). >>> >>> Thanks for the heads up -- Niklas has some additional series coming soon as described here: >>> >>> https://lore.kernel.org/linux-iommu/a10424adbe01a0fd40372cbd0736d11e517951a1.camel@linux.ibm.com/ >>> >>> So implementing the _pages() interfaces is soon up on the roadmap. But given what you say I wonder if this patch should just wait until the series that implements {map,unmap}_pages(). >> >> Perhaps, although the full change should be trivial enough that there's >> probably just as much argument for doing the whole thing in its own >> right for the sake of this cleanup. The main point is that >> S390_IOMMU_PGSIZES is not incorrect as such, it's just not spelling out >> the deliberate trick that it's achieving - everyone copied it from >> intel-iommu, but since that got converted to the new interfaces the >> original explanation is now gone. The only effect of "fixing" it in >> isolation right now will be to make large VFIO mappings slower. >> >> Robin. > > The patch changing to map_pages()/unmap_pages() is currently part of a > larger series of improvements, some of which are less trivial. So I'm > planning to send those as RFC first. Those include changing the > spin_lock protected list to RCU so the map/unmap can paralellize > better. Another one is atomic updates to the IOMMU tables to do away > with locks in map/unmap. So I think pulling that whole > series into this one isn't ideal. I could pull just the > map_pages()/unmap_pages() change though.
Yeah, literally just updating the s390_iommu_{map,unmap} function prototypes and replacing "size" with "pgsize * count" within is all that's needed to clean up this hack properly. That can (and probably should) be completely independent of other improvements deeper down.
Thanks, Robin.
> >> >>>>> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> >>>>> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com> >>>>> --- >>>>> drivers/iommu/s390-iommu.c | 9 +-------- >>>>> 1 file changed, 1 insertion(+), 8 deletions(-) >>>>> >>>>> diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c >>>>> index 94c444b909bd..6bf23e7830a2 100644 >>>>> --- a/drivers/iommu/s390-iommu.c >>>>> +++ b/drivers/iommu/s390-iommu.c >>>>> @@ -12,13 +12,6 @@ >>>>> #include <linux/sizes.h> >>>>> #include <asm/pci_dma.h> >>>>> -/* >>>>> - * Physically contiguous memory regions can be mapped with 4 KiB alignment, >>>>> - * we allow all page sizes that are an order of 4KiB (no special large page >>>>> - * support so far). >>>>> - */ >>>>> -#define S390_IOMMU_PGSIZES (~0xFFFUL) >>>>> - >>>>> static const struct iommu_ops s390_iommu_ops; >>>>> struct s390_domain { >>>>> @@ -350,7 +343,7 @@ static const struct iommu_ops s390_iommu_ops = { >>>>> .probe_device = s390_iommu_probe_device, >>>>> .release_device = s390_iommu_release_device, >>>>> .device_group = generic_device_group, >>>>> - .pgsize_bitmap = S390_IOMMU_PGSIZES, >>>>> + .pgsize_bitmap = SZ_4K, >>>>> .get_resv_regions = s390_iommu_get_resv_regions, >>>>> .default_domain_ops = &(const struct iommu_domain_ops) { >>>>> .attach_dev = s390_iommu_attach_device, > >
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