| Message ID | 20210408170123.8788-12-logang@deltatee.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Add new DMA mapping operation for P2PDMA | expand |
On Thu, Apr 08, 2021 at 11:01:18AM -0600, Logan Gunthorpe wrote: > When a PCI P2PDMA page is seen, set the IOVA length of the segment > to zero so that it is not mapped into the IOVA. Then, in finalise_sg(), > apply the appropriate bus address to the segment. The IOVA is not > created if the scatterlist only consists of P2PDMA pages. I expect P2P to work with systems that use ATS, so we'd want to see those systems have the IOMMU programmed with the bus address. Is it OK like this because the other logic prohibits all PCI cases that would lean on the IOMMU, like ATS, hairpinning through the root port, or transiting the root complex? If yes, the code deserves a big comment explaining this is incomplete, and I'd want to know we can finish this to include ATS at least based on this series. Jason
On 2021-04-27 1:43 p.m., Jason Gunthorpe wrote: > On Thu, Apr 08, 2021 at 11:01:18AM -0600, Logan Gunthorpe wrote: >> When a PCI P2PDMA page is seen, set the IOVA length of the segment >> to zero so that it is not mapped into the IOVA. Then, in finalise_sg(), >> apply the appropriate bus address to the segment. The IOVA is not >> created if the scatterlist only consists of P2PDMA pages. > > I expect P2P to work with systems that use ATS, so we'd want to see > those systems have the IOMMU programmed with the bus address. Oh, the paragraph you quote isn't quite as clear as it could be. The bus address is only used in specific circumstances depending on how the P2PDMA core code figures the addresses should be mapped (see the documentation for (upstream_bridge_distance()). The P2PDMA code currently doesn't have any provisions for ATS (I haven't had access to any such hardware) but I'm sure it wouldn't be too hard to add. Logan
On 4/8/21 10:01 AM, Logan Gunthorpe wrote: > When a PCI P2PDMA page is seen, set the IOVA length of the segment > to zero so that it is not mapped into the IOVA. Then, in finalise_sg(), > apply the appropriate bus address to the segment. The IOVA is not > created if the scatterlist only consists of P2PDMA pages. > > Similar to dma-direct, the sg_mark_pci_p2pdma() flag is used to > indicate bus address segments. On unmap, P2PDMA segments are skipped > over when determining the start and end IOVA addresses. > > With this change, the flags variable in the dma_map_ops is > set to DMA_F_PCI_P2PDMA_SUPPORTED to indicate support for > P2PDMA pages. > > Signed-off-by: Logan Gunthorpe <logang@deltatee.com> > --- > drivers/iommu/dma-iommu.c | 66 ++++++++++++++++++++++++++++++++++----- > 1 file changed, 58 insertions(+), 8 deletions(-) > > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c > index af765c813cc8..ef49635f9819 100644 > --- a/drivers/iommu/dma-iommu.c > +++ b/drivers/iommu/dma-iommu.c > @@ -20,6 +20,7 @@ > #include <linux/mm.h> > #include <linux/mutex.h> > #include <linux/pci.h> > +#include <linux/pci-p2pdma.h> > #include <linux/swiotlb.h> > #include <linux/scatterlist.h> > #include <linux/vmalloc.h> > @@ -864,6 +865,16 @@ static int __finalise_sg(struct device *dev, struct scatterlist *sg, int nents, > sg_dma_address(s) = DMA_MAPPING_ERROR; > sg_dma_len(s) = 0; > > + if (is_pci_p2pdma_page(sg_page(s)) && !s_iova_len) { Newbie question: I'm in the dark as to why the !s_iova_len check is there, can you please enlighten me? > + if (i > 0) > + cur = sg_next(cur); > + > + pci_p2pdma_map_bus_segment(s, cur); > + count++; > + cur_len = 0; > + continue; > + } > + This is really an if/else condition. And arguably, it would be better to split out two subroutines, and call one or the other depending on the result of if is_pci_p2pdma_page(), instead of this "continue" approach. > /* > * Now fill in the real DMA data. If... > * - there is a valid output segment to append to > @@ -961,10 +972,12 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, > struct iova_domain *iovad = &cookie->iovad; > struct scatterlist *s, *prev = NULL; > int prot = dma_info_to_prot(dir, dev_is_dma_coherent(dev), attrs); > + struct dev_pagemap *pgmap = NULL; > + enum pci_p2pdma_map_type map_type; > dma_addr_t iova; > size_t iova_len = 0; > unsigned long mask = dma_get_seg_boundary(dev); > - int i; > + int i, ret = 0; > > if (static_branch_unlikely(&iommu_deferred_attach_enabled) && > iommu_deferred_attach(dev, domain)) > @@ -993,6 +1006,31 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, > s_length = iova_align(iovad, s_length + s_iova_off); > s->length = s_length; > > + if (is_pci_p2pdma_page(sg_page(s))) { > + if (sg_page(s)->pgmap != pgmap) { > + pgmap = sg_page(s)->pgmap; > + map_type = pci_p2pdma_map_type(pgmap, dev, > + attrs); > + } > + > + switch (map_type) { > + case PCI_P2PDMA_MAP_BUS_ADDR: > + /* > + * A zero length will be ignored by > + * iommu_map_sg() and then can be detected > + * in __finalise_sg() to actually map the > + * bus address. > + */ > + s->length = 0; > + continue; > + case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE: > + break; > + default: > + ret = -EREMOTEIO; > + goto out_restore_sg; > + } > + } > + > /* > * Due to the alignment of our single IOVA allocation, we can > * depend on these assumptions about the segment boundary mask: > @@ -1015,6 +1053,9 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, > prev = s; > } > > + if (!iova_len) > + return __finalise_sg(dev, sg, nents, 0); > + ohhh, we're really slicing up this function pretty severely, what with the continue and the early out and several other control flow changes. I think it would be better to spend some time factoring this function into two cases, now that you're adding a second case for PCI P2PDMA. Roughly, two subroutines would do it. As it is, this leaves behind a routine that is extremely hard to mentally verify as correct. thanks,
Sorry, I think I missed responding to this one so here are the answers: On 2021-05-02 7:14 p.m., John Hubbard wrote: > On 4/8/21 10:01 AM, Logan Gunthorpe wrote: >> When a PCI P2PDMA page is seen, set the IOVA length of the segment >> to zero so that it is not mapped into the IOVA. Then, in finalise_sg(), >> apply the appropriate bus address to the segment. The IOVA is not >> created if the scatterlist only consists of P2PDMA pages. >> >> Similar to dma-direct, the sg_mark_pci_p2pdma() flag is used to >> indicate bus address segments. On unmap, P2PDMA segments are skipped >> over when determining the start and end IOVA addresses. >> >> With this change, the flags variable in the dma_map_ops is >> set to DMA_F_PCI_P2PDMA_SUPPORTED to indicate support for >> P2PDMA pages. >> >> Signed-off-by: Logan Gunthorpe <logang@deltatee.com> >> --- >> drivers/iommu/dma-iommu.c | 66 ++++++++++++++++++++++++++++++++++----- >> 1 file changed, 58 insertions(+), 8 deletions(-) >> >> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c >> index af765c813cc8..ef49635f9819 100644 >> --- a/drivers/iommu/dma-iommu.c >> +++ b/drivers/iommu/dma-iommu.c >> @@ -20,6 +20,7 @@ >> #include <linux/mm.h> >> #include <linux/mutex.h> >> #include <linux/pci.h> >> +#include <linux/pci-p2pdma.h> >> #include <linux/swiotlb.h> >> #include <linux/scatterlist.h> >> #include <linux/vmalloc.h> >> @@ -864,6 +865,16 @@ static int __finalise_sg(struct device *dev, >> struct scatterlist *sg, int nents, >> sg_dma_address(s) = DMA_MAPPING_ERROR; >> sg_dma_len(s) = 0; >> + if (is_pci_p2pdma_page(sg_page(s)) && !s_iova_len) { > > Newbie question: I'm in the dark as to why the !s_iova_len check is there, > can you please enlighten me? The loop in iommu_dma_map_sg() will decide what to do with P2PDMA pages. If it is to map it with the bus address it will set s_iova_len to zero so that no space is allocated in the IOVA. If it is to map it through the host bridge, then it it will leave s_iova_len alone and create the appropriate mapping with the CPU physical address. This condition notices that s_iova_len was set to zero and fills in a SG segment with the PCI bus address for that region. > >> + if (i > 0) >> + cur = sg_next(cur); >> + >> + pci_p2pdma_map_bus_segment(s, cur); >> + count++; >> + cur_len = 0; >> + continue; >> + } >> + > > This is really an if/else condition. And arguably, it would be better > to split out two subroutines, and call one or the other depending on > the result of if is_pci_p2pdma_page(), instead of this "continue" approach. I really disagree here. Putting the exceptional condition in it's own if statement and leaving the normal case un-indented is easier to read and understand. It also saves an extra level of indentation in code that is already starting to look a little squished. >> /* >> * Now fill in the real DMA data. If... >> * - there is a valid output segment to append to >> @@ -961,10 +972,12 @@ static int iommu_dma_map_sg(struct device *dev, >> struct scatterlist *sg, >> struct iova_domain *iovad = &cookie->iovad; >> struct scatterlist *s, *prev = NULL; >> int prot = dma_info_to_prot(dir, dev_is_dma_coherent(dev), attrs); >> + struct dev_pagemap *pgmap = NULL; >> + enum pci_p2pdma_map_type map_type; >> dma_addr_t iova; >> size_t iova_len = 0; >> unsigned long mask = dma_get_seg_boundary(dev); >> - int i; >> + int i, ret = 0; >> if (static_branch_unlikely(&iommu_deferred_attach_enabled) && >> iommu_deferred_attach(dev, domain)) >> @@ -993,6 +1006,31 @@ static int iommu_dma_map_sg(struct device *dev, >> struct scatterlist *sg, >> s_length = iova_align(iovad, s_length + s_iova_off); >> s->length = s_length; >> + if (is_pci_p2pdma_page(sg_page(s))) { >> + if (sg_page(s)->pgmap != pgmap) { >> + pgmap = sg_page(s)->pgmap; >> + map_type = pci_p2pdma_map_type(pgmap, dev, >> + attrs); >> + } >> + >> + switch (map_type) { >> + case PCI_P2PDMA_MAP_BUS_ADDR: >> + /* >> + * A zero length will be ignored by >> + * iommu_map_sg() and then can be detected >> + * in __finalise_sg() to actually map the >> + * bus address. >> + */ >> + s->length = 0; >> + continue; >> + case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE: >> + break; >> + default: >> + ret = -EREMOTEIO; >> + goto out_restore_sg; >> + } >> + } >> + >> /* >> * Due to the alignment of our single IOVA allocation, we can >> * depend on these assumptions about the segment boundary mask: >> @@ -1015,6 +1053,9 @@ static int iommu_dma_map_sg(struct device *dev, >> struct scatterlist *sg, >> prev = s; >> } >> + if (!iova_len) >> + return __finalise_sg(dev, sg, nents, 0); >> + > > ohhh, we're really slicing up this function pretty severely, what with the > continue and the early out and several other control flow changes. I think > it would be better to spend some time factoring this function into two > cases, now that you're adding a second case for PCI P2PDMA. Roughly, > two subroutines would do it. I don't see how we can factor this into two cases. The SGL may contain normal pages or P2PDMA pages or a mix of both and we have to create an IOVA area for all the regions that map the CPU physical address (ie normal pages and some P2PDMA pages) then also insert segments for any PCI bus address. > As it is, this leaves behind a routine that is extremely hard to mentally > verify as correct. Yes, this is tricky code, but not that incomprehensible. Most of the difficulty is in understanding how it works before adding the P2PDMA bits. There are two loops: one to prepare the IOVA region and another to fill in the SGL. We have to add cases in both loops to skip the segments that need to be mapped with the bus address in the first loop, and insert the dma SGL segments in the second loop. Logan
On 4/8/21 1:01 PM, Logan Gunthorpe wrote: > When a PCI P2PDMA page is seen, set the IOVA length of the segment > to zero so that it is not mapped into the IOVA. Then, in finalise_sg(), > apply the appropriate bus address to the segment. The IOVA is not > created if the scatterlist only consists of P2PDMA pages. > > Similar to dma-direct, the sg_mark_pci_p2pdma() flag is used to > indicate bus address segments. On unmap, P2PDMA segments are skipped > over when determining the start and end IOVA addresses. > > With this change, the flags variable in the dma_map_ops is > set to DMA_F_PCI_P2PDMA_SUPPORTED to indicate support for > P2PDMA pages. > > Signed-off-by: Logan Gunthorpe <logang@deltatee.com> So, this code prevents use of p2pdma using an IOMMU, which wasn't checked and short-circuited by other checks to use dma-direct? So my overall comment to this code & related comments is that it should be sprinkled with notes like "doesn't support IOMMU" and / or "TODO" when/if IOMMU is to be supported. Or, if IOMMU-based p2pdma isn't supported in these routines directly, where/how they will be supported? > --- > drivers/iommu/dma-iommu.c | 66 ++++++++++++++++++++++++++++++++++----- > 1 file changed, 58 insertions(+), 8 deletions(-) > > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c > index af765c813cc8..ef49635f9819 100644 > --- a/drivers/iommu/dma-iommu.c > +++ b/drivers/iommu/dma-iommu.c > @@ -20,6 +20,7 @@ > #include <linux/mm.h> > #include <linux/mutex.h> > #include <linux/pci.h> > +#include <linux/pci-p2pdma.h> > #include <linux/swiotlb.h> > #include <linux/scatterlist.h> > #include <linux/vmalloc.h> > @@ -864,6 +865,16 @@ static int __finalise_sg(struct device *dev, struct scatterlist *sg, int nents, > sg_dma_address(s) = DMA_MAPPING_ERROR; > sg_dma_len(s) = 0; > > + if (is_pci_p2pdma_page(sg_page(s)) && !s_iova_len) { > + if (i > 0) > + cur = sg_next(cur); > + > + pci_p2pdma_map_bus_segment(s, cur); > + count++; > + cur_len = 0; > + continue; > + } > + > /* > * Now fill in the real DMA data. If... > * - there is a valid output segment to append to > @@ -961,10 +972,12 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, > struct iova_domain *iovad = &cookie->iovad; > struct scatterlist *s, *prev = NULL; > int prot = dma_info_to_prot(dir, dev_is_dma_coherent(dev), attrs); > + struct dev_pagemap *pgmap = NULL; > + enum pci_p2pdma_map_type map_type; > dma_addr_t iova; > size_t iova_len = 0; > unsigned long mask = dma_get_seg_boundary(dev); > - int i; > + int i, ret = 0; > > if (static_branch_unlikely(&iommu_deferred_attach_enabled) && > iommu_deferred_attach(dev, domain)) > @@ -993,6 +1006,31 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, > s_length = iova_align(iovad, s_length + s_iova_off); > s->length = s_length; > > + if (is_pci_p2pdma_page(sg_page(s))) { > + if (sg_page(s)->pgmap != pgmap) { > + pgmap = sg_page(s)->pgmap; > + map_type = pci_p2pdma_map_type(pgmap, dev, > + attrs); > + } > + > + switch (map_type) { > + case PCI_P2PDMA_MAP_BUS_ADDR: > + /* > + * A zero length will be ignored by > + * iommu_map_sg() and then can be detected > + * in __finalise_sg() to actually map the > + * bus address. > + */ > + s->length = 0; > + continue; > + case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE: > + break; So, this 'short-circuits' the use of the IOMMU, silently? This seems ripe for users to enable IOMMU for secure computing reasons, and using/enabling p2pdma, and not realizing that it isn't as secure as 1+1=2 appears to be. If my understanding is wrong, please point me to the Documentation or code that corrects this mis-understanding. I could have missed a warning when both are enabled in a past patch set. Thanks. --dd > + default: > + ret = -EREMOTEIO; > + goto out_restore_sg; > + } > + } > + > /* > * Due to the alignment of our single IOVA allocation, we can > * depend on these assumptions about the segment boundary mask: > @@ -1015,6 +1053,9 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, > prev = s; > } > > + if (!iova_len) > + return __finalise_sg(dev, sg, nents, 0); > + > iova = iommu_dma_alloc_iova(domain, iova_len, dma_get_mask(dev), dev); > if (!iova) > goto out_restore_sg; > @@ -1032,13 +1073,13 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, > iommu_dma_free_iova(cookie, iova, iova_len, NULL); > out_restore_sg: > __invalidate_sg(sg, nents); > - return 0; > + return ret; > } > > static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg, > int nents, enum dma_data_direction dir, unsigned long attrs) > { > - dma_addr_t start, end; > + dma_addr_t end, start = DMA_MAPPING_ERROR; > struct scatterlist *tmp; > int i; > > @@ -1054,14 +1095,22 @@ static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg, > * The scatterlist segments are mapped into a single > * contiguous IOVA allocation, so this is incredibly easy. > */ > - start = sg_dma_address(sg); > - for_each_sg(sg_next(sg), tmp, nents - 1, i) { > + for_each_sg(sg, tmp, nents, i) { > + if (sg_is_pci_p2pdma(tmp)) { > + sg_unmark_pci_p2pdma(tmp); > + continue; > + } > if (sg_dma_len(tmp) == 0) > break; > - sg = tmp; > + > + if (start == DMA_MAPPING_ERROR) > + start = sg_dma_address(tmp); > + > + end = sg_dma_address(tmp) + sg_dma_len(tmp); > } > - end = sg_dma_address(sg) + sg_dma_len(sg); > - __iommu_dma_unmap(dev, start, end - start); > + > + if (start != DMA_MAPPING_ERROR) > + __iommu_dma_unmap(dev, start, end - start); > } > overall, fiddling with the generic dma-iommu code instead of using a dma-ops-based, p2pdma function that has it carved out and separated/refactored out to be cleaner seems less complicated, but I'm guessing you tried that and it was too complicated to do? --dd > static dma_addr_t iommu_dma_map_resource(struct device *dev, phys_addr_t phys, > @@ -1254,6 +1303,7 @@ static unsigned long iommu_dma_get_merge_boundary(struct device *dev) > } > > static const struct dma_map_ops iommu_dma_ops = { > + .flags = DMA_F_PCI_P2PDMA_SUPPORTED, wait, it's a const that's always turned on? shouldn't the define for this flag be 0 for non-p2pdma configs? > .alloc = iommu_dma_alloc, > .free = iommu_dma_free, > .alloc_pages = dma_common_alloc_pages,
On 2021-05-11 10:06 a.m., Don Dutile wrote: > On 4/8/21 1:01 PM, Logan Gunthorpe wrote: >> When a PCI P2PDMA page is seen, set the IOVA length of the segment >> to zero so that it is not mapped into the IOVA. Then, in finalise_sg(), >> apply the appropriate bus address to the segment. The IOVA is not >> created if the scatterlist only consists of P2PDMA pages. >> >> Similar to dma-direct, the sg_mark_pci_p2pdma() flag is used to >> indicate bus address segments. On unmap, P2PDMA segments are skipped >> over when determining the start and end IOVA addresses. >> >> With this change, the flags variable in the dma_map_ops is >> set to DMA_F_PCI_P2PDMA_SUPPORTED to indicate support for >> P2PDMA pages. >> >> Signed-off-by: Logan Gunthorpe <logang@deltatee.com> > So, this code prevents use of p2pdma using an IOMMU, which wasn't checked and > short-circuited by other checks to use dma-direct? No, not at all. This patch is adding support for p2pdma pages for IOMMUs that use the dma-iommu abstraction. Other arch specific IOMMUs that don't use the dma-iommu abstraction are left unsupported. Support would need to be added to them, or better yet; they should be ported to dma-iommu. > > So my overall comment to this code & related comments is that it should be sprinkled > with notes like "doesn't support IOMMU" and / or "TODO" when/if IOMMU is to be supported. > Or, if IOMMU-based p2pdma isn't supported in these routines directly, where/how they will be supported? > >> --- >> drivers/iommu/dma-iommu.c | 66 ++++++++++++++++++++++++++++++++++----- >> 1 file changed, 58 insertions(+), 8 deletions(-) >> >> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c >> index af765c813cc8..ef49635f9819 100644 >> --- a/drivers/iommu/dma-iommu.c >> +++ b/drivers/iommu/dma-iommu.c >> @@ -20,6 +20,7 @@ >> #include <linux/mm.h> >> #include <linux/mutex.h> >> #include <linux/pci.h> >> +#include <linux/pci-p2pdma.h> >> #include <linux/swiotlb.h> >> #include <linux/scatterlist.h> >> #include <linux/vmalloc.h> >> @@ -864,6 +865,16 @@ static int __finalise_sg(struct device *dev, struct scatterlist *sg, int nents, >> sg_dma_address(s) = DMA_MAPPING_ERROR; >> sg_dma_len(s) = 0; >> >> + if (is_pci_p2pdma_page(sg_page(s)) && !s_iova_len) { >> + if (i > 0) >> + cur = sg_next(cur); >> + >> + pci_p2pdma_map_bus_segment(s, cur); >> + count++; >> + cur_len = 0; >> + continue; >> + } >> + >> /* >> * Now fill in the real DMA data. If... >> * - there is a valid output segment to append to >> @@ -961,10 +972,12 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, >> struct iova_domain *iovad = &cookie->iovad; >> struct scatterlist *s, *prev = NULL; >> int prot = dma_info_to_prot(dir, dev_is_dma_coherent(dev), attrs); >> + struct dev_pagemap *pgmap = NULL; >> + enum pci_p2pdma_map_type map_type; >> dma_addr_t iova; >> size_t iova_len = 0; >> unsigned long mask = dma_get_seg_boundary(dev); >> - int i; >> + int i, ret = 0; >> >> if (static_branch_unlikely(&iommu_deferred_attach_enabled) && >> iommu_deferred_attach(dev, domain)) >> @@ -993,6 +1006,31 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, >> s_length = iova_align(iovad, s_length + s_iova_off); >> s->length = s_length; >> >> + if (is_pci_p2pdma_page(sg_page(s))) { >> + if (sg_page(s)->pgmap != pgmap) { >> + pgmap = sg_page(s)->pgmap; >> + map_type = pci_p2pdma_map_type(pgmap, dev, >> + attrs); >> + } >> + >> + switch (map_type) { >> + case PCI_P2PDMA_MAP_BUS_ADDR: >> + /* >> + * A zero length will be ignored by >> + * iommu_map_sg() and then can be detected >> + * in __finalise_sg() to actually map the >> + * bus address. >> + */ >> + s->length = 0; >> + continue; > >> + case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE: >> + break; > So, this 'short-circuits' the use of the IOMMU, silently? > This seems ripe for users to enable IOMMU for secure computing reasons, and using/enabling p2pdma, > and not realizing that it isn't as secure as 1+1=2 appears to be. > If my understanding is wrong, please point me to the Documentation or code that corrects this mis-understanding. I could have missed a warning when both are enabled in a past patch set. Yes, you've misunderstood this. Part of this dovetails with your comment about the documentation for PCI_P2PDMA_MAP_THRU_HOST_BRIDGE. This does not short circuit the IOMMU in any way. THRU_HOST_BRIDGE mode means the TLPs for this transaction will hit the CPU/HOST BRIDGE and thus the IOMMU has to be involved. In this case the IOMMU is programmed with the physical address of the memory (which is normal) and everything works. One could argue the PCI_P2PDMA_MAP_BUS_ADDR is short circuiting the IOMMU by using PCI bus address in the DMA transaction. But this requires the user to do special setup with the ACS bits ahead of time (not part of this series). For the user to use the BUS_ADDR with an IOMMU, they need to specifically disable the ACS redirect bits on specific PCI switch bridge ports using a kernel command line option. When they do this, the IOMMU code will put those devices in the same IOMMU group thus making it impossible for the user to use devices that can do P2PDMA transactions together in different security domains. This was all hashed out in the original P2PDMA patchset and does make sense. >> + default: >> + ret = -EREMOTEIO; >> + goto out_restore_sg; >> + } >> + } >> + >> /* >> * Due to the alignment of our single IOVA allocation, we can >> * depend on these assumptions about the segment boundary mask: >> @@ -1015,6 +1053,9 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, >> prev = s; >> } >> >> + if (!iova_len) >> + return __finalise_sg(dev, sg, nents, 0); >> + >> iova = iommu_dma_alloc_iova(domain, iova_len, dma_get_mask(dev), dev); >> if (!iova) >> goto out_restore_sg; >> @@ -1032,13 +1073,13 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, >> iommu_dma_free_iova(cookie, iova, iova_len, NULL); >> out_restore_sg: >> __invalidate_sg(sg, nents); >> - return 0; >> + return ret; >> } >> >> static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg, >> int nents, enum dma_data_direction dir, unsigned long attrs) >> { >> - dma_addr_t start, end; >> + dma_addr_t end, start = DMA_MAPPING_ERROR; >> struct scatterlist *tmp; >> int i; >> >> @@ -1054,14 +1095,22 @@ static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg, >> * The scatterlist segments are mapped into a single >> * contiguous IOVA allocation, so this is incredibly easy. >> */ >> - start = sg_dma_address(sg); >> - for_each_sg(sg_next(sg), tmp, nents - 1, i) { >> + for_each_sg(sg, tmp, nents, i) { >> + if (sg_is_pci_p2pdma(tmp)) { >> + sg_unmark_pci_p2pdma(tmp); >> + continue; >> + } >> if (sg_dma_len(tmp) == 0) >> break; >> - sg = tmp; >> + >> + if (start == DMA_MAPPING_ERROR) >> + start = sg_dma_address(tmp); >> + >> + end = sg_dma_address(tmp) + sg_dma_len(tmp); >> } >> - end = sg_dma_address(sg) + sg_dma_len(sg); >> - __iommu_dma_unmap(dev, start, end - start); >> + >> + if (start != DMA_MAPPING_ERROR) >> + __iommu_dma_unmap(dev, start, end - start); >> } >> > overall, fiddling with the generic dma-iommu code instead of using a dma-ops-based, p2pdma function that has it carved out and separated/refactored out to be cleaner seems less complicated, but I'm guessing you tried that and it was too complicated to do? I don't think you've understood this code correctly. What it does can't be done in the dma-ops. >> static const struct dma_map_ops iommu_dma_ops = { >> + .flags = DMA_F_PCI_P2PDMA_SUPPORTED, > wait, it's a const that's always turned on? > shouldn't the define for this flag be 0 for non-p2pdma configs? All this flag is saying is that iommu_dma_map_sg() has support for handling P2PDMA pages. Yes this is a const. The point is to reject it for map_sg implementations that have not done the above work (ie. arm_iommu_map_sg). Hopefully, more of the arch-specific implementations will convert to the generic dma-iommu code in time but those that don't simply won't support P2PDMA until they do (or add their own support). Logan
diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c index af765c813cc8..ef49635f9819 100644 --- a/drivers/iommu/dma-iommu.c +++ b/drivers/iommu/dma-iommu.c @@ -20,6 +20,7 @@ #include <linux/mm.h> #include <linux/mutex.h> #include <linux/pci.h> +#include <linux/pci-p2pdma.h> #include <linux/swiotlb.h> #include <linux/scatterlist.h> #include <linux/vmalloc.h> @@ -864,6 +865,16 @@ static int __finalise_sg(struct device *dev, struct scatterlist *sg, int nents, sg_dma_address(s) = DMA_MAPPING_ERROR; sg_dma_len(s) = 0; + if (is_pci_p2pdma_page(sg_page(s)) && !s_iova_len) { + if (i > 0) + cur = sg_next(cur); + + pci_p2pdma_map_bus_segment(s, cur); + count++; + cur_len = 0; + continue; + } + /* * Now fill in the real DMA data. If... * - there is a valid output segment to append to @@ -961,10 +972,12 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, struct iova_domain *iovad = &cookie->iovad; struct scatterlist *s, *prev = NULL; int prot = dma_info_to_prot(dir, dev_is_dma_coherent(dev), attrs); + struct dev_pagemap *pgmap = NULL; + enum pci_p2pdma_map_type map_type; dma_addr_t iova; size_t iova_len = 0; unsigned long mask = dma_get_seg_boundary(dev); - int i; + int i, ret = 0; if (static_branch_unlikely(&iommu_deferred_attach_enabled) && iommu_deferred_attach(dev, domain)) @@ -993,6 +1006,31 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, s_length = iova_align(iovad, s_length + s_iova_off); s->length = s_length; + if (is_pci_p2pdma_page(sg_page(s))) { + if (sg_page(s)->pgmap != pgmap) { + pgmap = sg_page(s)->pgmap; + map_type = pci_p2pdma_map_type(pgmap, dev, + attrs); + } + + switch (map_type) { + case PCI_P2PDMA_MAP_BUS_ADDR: + /* + * A zero length will be ignored by + * iommu_map_sg() and then can be detected + * in __finalise_sg() to actually map the + * bus address. + */ + s->length = 0; + continue; + case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE: + break; + default: + ret = -EREMOTEIO; + goto out_restore_sg; + } + } + /* * Due to the alignment of our single IOVA allocation, we can * depend on these assumptions about the segment boundary mask: @@ -1015,6 +1053,9 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, prev = s; } + if (!iova_len) + return __finalise_sg(dev, sg, nents, 0); + iova = iommu_dma_alloc_iova(domain, iova_len, dma_get_mask(dev), dev); if (!iova) goto out_restore_sg; @@ -1032,13 +1073,13 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, iommu_dma_free_iova(cookie, iova, iova_len, NULL); out_restore_sg: __invalidate_sg(sg, nents); - return 0; + return ret; } static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg, int nents, enum dma_data_direction dir, unsigned long attrs) { - dma_addr_t start, end; + dma_addr_t end, start = DMA_MAPPING_ERROR; struct scatterlist *tmp; int i; @@ -1054,14 +1095,22 @@ static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg, * The scatterlist segments are mapped into a single * contiguous IOVA allocation, so this is incredibly easy. */ - start = sg_dma_address(sg); - for_each_sg(sg_next(sg), tmp, nents - 1, i) { + for_each_sg(sg, tmp, nents, i) { + if (sg_is_pci_p2pdma(tmp)) { + sg_unmark_pci_p2pdma(tmp); + continue; + } if (sg_dma_len(tmp) == 0) break; - sg = tmp; + + if (start == DMA_MAPPING_ERROR) + start = sg_dma_address(tmp); + + end = sg_dma_address(tmp) + sg_dma_len(tmp); } - end = sg_dma_address(sg) + sg_dma_len(sg); - __iommu_dma_unmap(dev, start, end - start); + + if (start != DMA_MAPPING_ERROR) + __iommu_dma_unmap(dev, start, end - start); } static dma_addr_t iommu_dma_map_resource(struct device *dev, phys_addr_t phys, @@ -1254,6 +1303,7 @@ static unsigned long iommu_dma_get_merge_boundary(struct device *dev) } static const struct dma_map_ops iommu_dma_ops = { + .flags = DMA_F_PCI_P2PDMA_SUPPORTED, .alloc = iommu_dma_alloc, .free = iommu_dma_free, .alloc_pages = dma_common_alloc_pages,
When a PCI P2PDMA page is seen, set the IOVA length of the segment to zero so that it is not mapped into the IOVA. Then, in finalise_sg(), apply the appropriate bus address to the segment. The IOVA is not created if the scatterlist only consists of P2PDMA pages. Similar to dma-direct, the sg_mark_pci_p2pdma() flag is used to indicate bus address segments. On unmap, P2PDMA segments are skipped over when determining the start and end IOVA addresses. With this change, the flags variable in the dma_map_ops is set to DMA_F_PCI_P2PDMA_SUPPORTED to indicate support for P2PDMA pages. Signed-off-by: Logan Gunthorpe <logang@deltatee.com> --- drivers/iommu/dma-iommu.c | 66 ++++++++++++++++++++++++++++++++++----- 1 file changed, 58 insertions(+), 8 deletions(-)