| Message ID | 20210408170123.8788-4-logang@deltatee.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add new DMA mapping operation for P2PDMA | expand |
On 4/8/21 10:01 AM, Logan Gunthorpe wrote: > Attempt to find the mapping type for P2PDMA pages on the first > DMA map attempt if it has not been done ahead of time. > > Previously, the mapping type was expected to be calculated ahead of > time, but if pages are to come from userspace then there's no > way to ensure the path was checked ahead of time. > > Signed-off-by: Logan Gunthorpe <logang@deltatee.com> > --- > drivers/pci/p2pdma.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c > index 473a08940fbc..2574a062a255 100644 > --- a/drivers/pci/p2pdma.c > +++ b/drivers/pci/p2pdma.c > @@ -825,11 +825,18 @@ EXPORT_SYMBOL_GPL(pci_p2pmem_publish); > static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct pci_dev *provider, > struct pci_dev *client) > { > + enum pci_p2pdma_map_type ret; > + > if (!provider->p2pdma) > return PCI_P2PDMA_MAP_NOT_SUPPORTED; > > - return xa_to_value(xa_load(&provider->p2pdma->map_types, > - map_types_idx(client))); > + ret = xa_to_value(xa_load(&provider->p2pdma->map_types, > + map_types_idx(client))); > + if (ret != PCI_P2PDMA_MAP_UNKNOWN) > + return ret; > + > + return upstream_bridge_distance_warn(provider, client, NULL, > + GFP_ATOMIC); Returning a "bridge distance" from a "get map type" routine is jarring, and I think it is because of a pre-existing problem: the above function is severely misnamed. Let's try renaming it (and the other one) to approximately: upstream_bridge_map_type_warn() upstream_bridge_map_type() ...and that should fix that. Well, that, plus tweaking the kernel doc comments, which are also confused. I think someone started off thinking about distances through PCIe, but in the end, the routine boils down to just a few situations that are not distances at all. Also, the above will read a little better if it is written like this: ret = xa_to_value(xa_load(&provider->p2pdma->map_types, map_types_idx(client))); if (ret == PCI_P2PDMA_MAP_UNKNOWN) ret = upstream_bridge_map_type_warn(provider, client, NULL, GFP_ATOMIC); return ret; > } > > static int __pci_p2pdma_map_sg(struct pci_p2pdma_pagemap *p2p_pgmap, > @@ -877,7 +884,6 @@ int pci_p2pdma_map_sg_attrs(struct device *dev, struct scatterlist *sg, > case PCI_P2PDMA_MAP_BUS_ADDR: > return __pci_p2pdma_map_sg(p2p_pgmap, dev, sg, nents); > default: > - WARN_ON_ONCE(1); Why? Or at least, why, in this patch? It looks like an accidental leftover from something, seeing as how it is not directly related to the patch, and is not mentioned at all. thanks,
On 2021-05-02 1:58 p.m., John Hubbard wrote: > On 4/8/21 10:01 AM, Logan Gunthorpe wrote: >> Attempt to find the mapping type for P2PDMA pages on the first >> DMA map attempt if it has not been done ahead of time. >> >> Previously, the mapping type was expected to be calculated ahead of >> time, but if pages are to come from userspace then there's no >> way to ensure the path was checked ahead of time. >> >> Signed-off-by: Logan Gunthorpe <logang@deltatee.com> >> --- >> drivers/pci/p2pdma.c | 12 +++++++++--- >> 1 file changed, 9 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c >> index 473a08940fbc..2574a062a255 100644 >> --- a/drivers/pci/p2pdma.c >> +++ b/drivers/pci/p2pdma.c >> @@ -825,11 +825,18 @@ EXPORT_SYMBOL_GPL(pci_p2pmem_publish); >> static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct pci_dev *provider, >> struct pci_dev *client) >> { >> + enum pci_p2pdma_map_type ret; >> + >> if (!provider->p2pdma) >> return PCI_P2PDMA_MAP_NOT_SUPPORTED; >> >> - return xa_to_value(xa_load(&provider->p2pdma->map_types, >> - map_types_idx(client))); >> + ret = xa_to_value(xa_load(&provider->p2pdma->map_types, >> + map_types_idx(client))); >> + if (ret != PCI_P2PDMA_MAP_UNKNOWN) >> + return ret; >> + >> + return upstream_bridge_distance_warn(provider, client, NULL, >> + GFP_ATOMIC); > > Returning a "bridge distance" from a "get map type" routine is jarring, > and I think it is because of a pre-existing problem: the above function > is severely misnamed. Let's try renaming it (and the other one) to > approximately: > > upstream_bridge_map_type_warn() > upstream_bridge_map_type() > > ...and that should fix that. Well, that, plus tweaking the kernel doc > comments, which are also confused. I think someone started off thinking > about distances through PCIe, but in the end, the routine boils down to > just a few situations that are not distances at all. > > Also, the above will read a little better if it is written like this: > > ret = xa_to_value(xa_load(&provider->p2pdma->map_types, > map_types_idx(client))); > > if (ret == PCI_P2PDMA_MAP_UNKNOWN) > ret = upstream_bridge_map_type_warn(provider, client, NULL, > GFP_ATOMIC); > > return ret; > > >> } I agree that some of this has evolved in a way that some of the names are a bit odd now. Could definitely use a cleanup, but that's not really part of this series. When I have some time I can look at doing a cleanup series to help with some of this. >> static int __pci_p2pdma_map_sg(struct pci_p2pdma_pagemap *p2p_pgmap, >> @@ -877,7 +884,6 @@ int pci_p2pdma_map_sg_attrs(struct device *dev, struct scatterlist *sg, >> case PCI_P2PDMA_MAP_BUS_ADDR: >> return __pci_p2pdma_map_sg(p2p_pgmap, dev, sg, nents); >> default: >> - WARN_ON_ONCE(1); > > Why? Or at least, why, in this patch? It looks like an accidental > leftover from something, seeing as how it is not directly related to the > patch, and is not mentioned at all. Before this patch, it was required that users of P2PDMA call pci_p2pdma_distance_many() in some form before calling pci_p2pdma_map_sg(). So, by convention, a usable map type had to already be in the cache. The warning was there to yell at anyone who wrote code that violated that convention. This patch removes that convention and allows users to map P2PDMA pages sight unseen and if the mapping type isn't in the cache, then it will determine the mapping type at dma mapping time. Thus, the warning can be removed and the function can fail normally if the mapping is unsupported. Logan
On 5/3/21 9:17 AM, Logan Gunthorpe wrote: >> Returning a "bridge distance" from a "get map type" routine is jarring, >> and I think it is because of a pre-existing problem: the above function >> is severely misnamed. Let's try renaming it (and the other one) to >> approximately: >> >> upstream_bridge_map_type_warn() >> upstream_bridge_map_type() >> >> ...and that should fix that. Well, that, plus tweaking the kernel doc >> comments, which are also confused. I think someone started off thinking >> about distances through PCIe, but in the end, the routine boils down to >> just a few situations that are not distances at all. >> >> Also, the above will read a little better if it is written like this: >> >> ret = xa_to_value(xa_load(&provider->p2pdma->map_types, >> map_types_idx(client))); >> >> if (ret == PCI_P2PDMA_MAP_UNKNOWN) >> ret = upstream_bridge_map_type_warn(provider, client, NULL, >> GFP_ATOMIC); >> >> return ret; >> >> >>> } > > I agree that some of this has evolved in a way that some of the names > are a bit odd now. Could definitely use a cleanup, but that's not really > part of this series. When I have some time I can look at doing a cleanup > series to help with some of this. I'm OK with doing cleanup later. I just tend to call it out when I see it. > >>> static int __pci_p2pdma_map_sg(struct pci_p2pdma_pagemap *p2p_pgmap, >>> @@ -877,7 +884,6 @@ int pci_p2pdma_map_sg_attrs(struct device *dev, struct scatterlist *sg, >>> case PCI_P2PDMA_MAP_BUS_ADDR: >>> return __pci_p2pdma_map_sg(p2p_pgmap, dev, sg, nents); >>> default: >>> - WARN_ON_ONCE(1); >> >> Why? Or at least, why, in this patch? It looks like an accidental >> leftover from something, seeing as how it is not directly related to the >> patch, and is not mentioned at all. > > Before this patch, it was required that users of P2PDMA call > pci_p2pdma_distance_many() in some form before calling > pci_p2pdma_map_sg(). So, by convention, a usable map type had to already > be in the cache. The warning was there to yell at anyone who wrote code > that violated that convention. > > This patch removes that convention and allows users to map P2PDMA pages > sight unseen and if the mapping type isn't in the cache, then it will > determine the mapping type at dma mapping time. Thus, the warning can be > removed and the function can fail normally if the mapping is unsupported. > Let's add some of those words to the commit description, perhaps, it's nice to have. Obviously a minor point though. thanks,
On Mon, May 03, 2021 at 10:17:59AM -0600, Logan Gunthorpe wrote: > I agree that some of this has evolved in a way that some of the names > are a bit odd now. Could definitely use a cleanup, but that's not really > part of this series. When I have some time I can look at doing a cleanup > series to help with some of this. I think adding it to the series would be very helpful.
On 2021-05-03 12:35 p.m., Christoph Hellwig wrote: > On Mon, May 03, 2021 at 10:17:59AM -0600, Logan Gunthorpe wrote: >> I agree that some of this has evolved in a way that some of the names >> are a bit odd now. Could definitely use a cleanup, but that's not really >> part of this series. When I have some time I can look at doing a cleanup >> series to help with some of this. > > I think adding it to the series would be very helpful. Ok, I'll prepend a handful of cleanup patches. Logan
On 5/2/21 3:58 PM, John Hubbard wrote: > On 4/8/21 10:01 AM, Logan Gunthorpe wrote: >> Attempt to find the mapping type for P2PDMA pages on the first >> DMA map attempt if it has not been done ahead of time. >> >> Previously, the mapping type was expected to be calculated ahead of >> time, but if pages are to come from userspace then there's no >> way to ensure the path was checked ahead of time. >> >> Signed-off-by: Logan Gunthorpe <logang@deltatee.com> >> --- >> drivers/pci/p2pdma.c | 12 +++++++++--- >> 1 file changed, 9 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c >> index 473a08940fbc..2574a062a255 100644 >> --- a/drivers/pci/p2pdma.c >> +++ b/drivers/pci/p2pdma.c >> @@ -825,11 +825,18 @@ EXPORT_SYMBOL_GPL(pci_p2pmem_publish); >> static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct pci_dev *provider, >> struct pci_dev *client) >> { >> + enum pci_p2pdma_map_type ret; >> + >> if (!provider->p2pdma) >> return PCI_P2PDMA_MAP_NOT_SUPPORTED; >> - return xa_to_value(xa_load(&provider->p2pdma->map_types, >> - map_types_idx(client))); >> + ret = xa_to_value(xa_load(&provider->p2pdma->map_types, >> + map_types_idx(client))); >> + if (ret != PCI_P2PDMA_MAP_UNKNOWN) >> + return ret; >> + >> + return upstream_bridge_distance_warn(provider, client, NULL, >> + GFP_ATOMIC); > > Returning a "bridge distance" from a "get map type" routine is jarring, > and I think it is because of a pre-existing problem: the above function > is severely misnamed. Let's try renaming it (and the other one) to > approximately: > > upstream_bridge_map_type_warn() > upstream_bridge_map_type() > > ...and that should fix that. Well, that, plus tweaking the kernel doc > comments, which are also confused. I think someone started off thinking > about distances through PCIe, but in the end, the routine boils down to > just a few situations that are not distances at all. > +1. didn't like the 'distance' check for a 'connection check" in the beginning, and looks like this is the time to clean it out. :) > Also, the above will read a little better if it is written like this: > > ret = xa_to_value(xa_load(&provider->p2pdma->map_types, > map_types_idx(client))); > > if (ret == PCI_P2PDMA_MAP_UNKNOWN) > ret = upstream_bridge_map_type_warn(provider, client, NULL, > GFP_ATOMIC); > > return ret; > > >> } >> static int __pci_p2pdma_map_sg(struct pci_p2pdma_pagemap *p2p_pgmap, >> @@ -877,7 +884,6 @@ int pci_p2pdma_map_sg_attrs(struct device *dev, struct scatterlist *sg, >> case PCI_P2PDMA_MAP_BUS_ADDR: >> return __pci_p2pdma_map_sg(p2p_pgmap, dev, sg, nents); >> default: >> - WARN_ON_ONCE(1); > > Why? Or at least, why, in this patch? It looks like an accidental > leftover from something, seeing as how it is not directly related to the > patch, and is not mentioned at all. > > > thanks,
diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c index 473a08940fbc..2574a062a255 100644 --- a/drivers/pci/p2pdma.c +++ b/drivers/pci/p2pdma.c @@ -825,11 +825,18 @@ EXPORT_SYMBOL_GPL(pci_p2pmem_publish); static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct pci_dev *provider, struct pci_dev *client) { + enum pci_p2pdma_map_type ret; + if (!provider->p2pdma) return PCI_P2PDMA_MAP_NOT_SUPPORTED; - return xa_to_value(xa_load(&provider->p2pdma->map_types, - map_types_idx(client))); + ret = xa_to_value(xa_load(&provider->p2pdma->map_types, + map_types_idx(client))); + if (ret != PCI_P2PDMA_MAP_UNKNOWN) + return ret; + + return upstream_bridge_distance_warn(provider, client, NULL, + GFP_ATOMIC); } static int __pci_p2pdma_map_sg(struct pci_p2pdma_pagemap *p2p_pgmap, @@ -877,7 +884,6 @@ int pci_p2pdma_map_sg_attrs(struct device *dev, struct scatterlist *sg, case PCI_P2PDMA_MAP_BUS_ADDR: return __pci_p2pdma_map_sg(p2p_pgmap, dev, sg, nents); default: - WARN_ON_ONCE(1); return 0; } }
Attempt to find the mapping type for P2PDMA pages on the first DMA map attempt if it has not been done ahead of time. Previously, the mapping type was expected to be calculated ahead of time, but if pages are to come from userspace then there's no way to ensure the path was checked ahead of time. Signed-off-by: Logan Gunthorpe <logang@deltatee.com> --- drivers/pci/p2pdma.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)