Messages in this thread | | | Subject | Re: [RFC PATCH 2/3] iommu/dma-iommu: Support iovad->granule > PAGE_SIZE | From | Robin Murphy <> | Date | Thu, 12 Aug 2021 13:43:53 +0100 |
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On 2021-08-11 21:18, Sven Peter wrote: > > > On Tue, Aug 10, 2021, at 11:51, Robin Murphy wrote: >> On 2021-08-09 21:45, Sven Peter wrote: >>> >>> >>> On Mon, Aug 9, 2021, at 19:41, Robin Murphy wrote: >>>> On 2021-08-07 12:47, Sven Peter via iommu wrote: >>>>> >>>>> >>>>> On Fri, Aug 6, 2021, at 20:04, Robin Murphy wrote: >>>>>> On 2021-08-06 16:55, Sven Peter via iommu wrote: >>>>>>> @@ -1006,6 +1019,31 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, >>>>>>> if (dev_is_untrusted(dev)) >>>>>>> return iommu_dma_map_sg_swiotlb(dev, sg, nents, dir, attrs); >>>>>>> >>>>>>> + /* >>>>>>> + * If the IOMMU pagesize is larger than the CPU pagesize we will >>>>>>> + * very likely run into sgs with a physical address that is not aligned >>>>>>> + * to an IOMMU page boundary. Fall back to just mapping every entry >>>>>>> + * independently with __iommu_dma_map then. >>>>>> >>>>>> Scatterlist segments often don't have nicely aligned ends, which is why >>>>>> we already align things to IOVA granules in main loop here. I think in >>>>>> principle we'd just need to move the non-IOVA-aligned part of the >>>>>> address from sg->page to sg->offset in the temporary transformation for >>>>>> the rest of the assumptions to hold. I don't blame you for being timid >>>>>> about touching that, though - it took me 3 tries to get right when I >>>>>> first wrote it... >>>>>> >>>>> >>>>> >>>>> I've spent some time with that code now and I think we cannot use it >>>>> but have to fall back to iommu_dma_map_sg_swiotlb (even though that swiotlb >>>>> part is a lie then): >>>>> >>>>> When we have sg_phys(s) = 0x802e65000 with s->offset = 0 the paddr >>>>> is aligned to PAGE_SIZE but has an offset of 0x1000 from something >>>>> the IOMMU can map. >>>>> Now this would result in s->offset = -0x1000 which is already weird >>>>> enough. >>>>> Offset is unsigned (and 32bit) so this will actually look like >>>>> s->offset = 0xfffff000 then, which isn't much better. >>>>> And then sg_phys(s) = 0x902e64000 (instead of 0x802e64000) and >>>>> we'll map some random memory in iommu_map_sg_atomic and a little bit later >>>>> everything explodes. >>>>> >>>>> Now I could probably adjust the phys addr backwards and make sure offset is >>>>> always positive (and possibly larger than PAGE_SIZE) and later restore it >>>>> in __finalise_sg then but I feel like that's pushing this a little bit too far. >>>> >>>> Yes, that's what I meant. At a quick guess, something like the >>>> completely untested diff below. >>> >>> That unfortunately results in unaligned mappings >> >> You mean it even compiles!? :D > > I was more impressed that it already almost worked correctly :) > >> >>> [ 9.630334] iommu: unaligned: iova 0xbff40000 pa 0x0000000801a3b000 size 0x4000 min_pagesz 0x4000 >>> >>> I'll take a closer look later this week and see if I can fix it. >> >> On reflection, "s->offset ^ s_iova_off" is definitely wrong, that more >> likely wants to be "s->offset & ~s_iova_off". >> >> Robin. >> > > > If I change > > sg_set_page(s, phys_to_page(sg_phys(s)), s_length, > s_iova_off & ~PAGE_MASK); > > in __finalise_sg (and the same thing in __invalidate_sg) to > > sg_set_page(s, phys_to_page(sg_phys(s) + s_iova_off), s_length, > s_iova_off & ~PAGE_MASK); > > then it also restores the original fields correctly.
Ah, good point, once again this proves to be right on the limit of how many moving parts I can hold in my head without working it through on paper (or in a debugger). FWIW my thought there was that sg_phys(s) would be enough to "re-normalise" things from a state where s->page_link was rounded down and s->offset held the PAGE_SIZE multiple (which is what the XOR did do), but of course that wasn't right to begin with. In fact, s->offset must always be negligible when restoring so you could arguably open-code page_to_phys(sg_page(s)), but that might be a bit too much of a mouthful for a theoretical micro-optimisation (note that trying to avoid the phys_addr_t round-trip by offsetting the page pointer itself might appear to work for SPARSEMEM_VMEMMAP, but I'm pretty sure it's not valid in general).
> What is the proper way to credit you for coming up with this? > Do you create the commit and I apply it to my local tree and > include it in my submission once I have fixed the other > issues? Or do I create the commit and put a Suggested-by > in the message?
Suggested-by is fine by me, but if you feel there's enough of my diff left that you haven't had to put right then you're also welcome to have these instead:
Co-developed-by: Robin Murphy <robin.murphy@arm.com> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Cheers, Robin.
> > > Either way, here's the patch that I have right now: > > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c > index 7ce74476699d..ba31dc59566d 100644 > --- a/drivers/iommu/dma-iommu.c > +++ b/drivers/iommu/dma-iommu.c > @@ -907,8 +907,8 @@ static int __finalise_sg(struct device *dev, struct scatterlist *sg, int nents, > unsigned int s_length = sg_dma_len(s); > unsigned int s_iova_len = s->length; > > - s->offset += s_iova_off; > - s->length = s_length; > + sg_set_page(s, phys_to_page(sg_phys(s) + s_iova_off), s_length, > + s_iova_off & ~PAGE_MASK); > sg_dma_address(s) = DMA_MAPPING_ERROR; > sg_dma_len(s) = 0; > > @@ -952,10 +952,11 @@ static void __invalidate_sg(struct scatterlist *sg, int nents) > int i; > > for_each_sg(sg, s, nents, i) { > - if (sg_dma_address(s) != DMA_MAPPING_ERROR) > - s->offset += sg_dma_address(s); > if (sg_dma_len(s)) > - s->length = sg_dma_len(s); > + sg_set_page(s, > + phys_to_page(sg_phys(s) + sg_dma_address(s)), > + sg_dma_len(s), > + sg_dma_address(s) & ~PAGE_MASK); > sg_dma_address(s) = DMA_MAPPING_ERROR; > sg_dma_len(s) = 0; > } > @@ -1031,15 +1032,16 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, > * stashing the unaligned parts in the as-yet-unused DMA fields. > */ > for_each_sg(sg, s, nents, i) { > - size_t s_iova_off = iova_offset(iovad, s->offset); > + phys_addr_t s_phys = sg_phys(s); > + size_t s_iova_off = iova_offset(iovad, s_phys); > size_t s_length = s->length; > size_t pad_len = (mask - iova_len + 1) & mask; > > sg_dma_address(s) = s_iova_off; > sg_dma_len(s) = s_length; > - s->offset -= s_iova_off; > s_length = iova_align(iovad, s_length + s_iova_off); > - s->length = s_length; > + sg_set_page(s, phys_to_page(s_phys - s_iova_off), > + s_length, s->offset & ~s_iova_off); > > /* > * Due to the alignment of our single IOVA allocation, we can > > > > > > Sven >
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