search for: virtio_f_platform_dma

On Wed, 2018-08-01 at 01:36 -0700, Christoph Hellwig wrote: > We just need to figure out how to deal with devices that deviate > from the default. One things is that VIRTIO_F_IOMMU_PLATFORM really > should become VIRTIO_F_PLATFORM_DMA to cover the cases of non-iommu > dma tweaks (offsets, cache flushing), which seems well in spirit of > the original design. I don't completely agree: 1 - VIRTIO_F_IOMMU_PLATFORM is a property of the "other side", ie qemu for example. It indicates that the peer bypasses the n...

On Wed, 2018-08-01 at 01:36 -0700, Christoph Hellwig wrote: > We just need to figure out how to deal with devices that deviate > from the default. One things is that VIRTIO_F_IOMMU_PLATFORM really > should become VIRTIO_F_PLATFORM_DMA to cover the cases of non-iommu > dma tweaks (offsets, cache flushing), which seems well in spirit of > the original design. I don't completely agree: 1 - VIRTIO_F_IOMMU_PLATFORM is a property of the "other side", ie qemu for example. It indicates that the peer bypasses the n...

On Tue, Jul 31, 2018 at 03:36:22PM -0500, Benjamin Herrenschmidt wrote: > On Tue, 2018-07-31 at 10:30 -0700, Christoph Hellwig wrote: > > > However the question people raise is that DMA API is already full of > > > arch-specific tricks the likes of which are outlined in your post linked > > > above. How is this one much worse? > > > > None of these warts

On Tue, Jul 31, 2018 at 03:36:22PM -0500, Benjamin Herrenschmidt wrote: > On Tue, 2018-07-31 at 10:30 -0700, Christoph Hellwig wrote: > > > However the question people raise is that DMA API is already full of > > > arch-specific tricks the likes of which are outlined in your post linked > > > above. How is this one much worse? > > > > None of these warts

...her side", ie qemu > > for example. It indicates that the peer bypasses the normal platform > > iommu. The platform code in the guest has no real way to know that this > > is the case, this is a specific "feature" of the qemu implementation. > > > > 2 - VIRTIO_F_PLATFORM_DMA (or whatever you want to call it), is a > > property of the guest platform itself (not qemu), there's no way the > > "peer" can advertize it via the virtio negociated flags. At least for > > us. I don't know for sure whether that would be workable for the ARM &gt...

...her side", ie qemu > > for example. It indicates that the peer bypasses the normal platform > > iommu. The platform code in the guest has no real way to know that this > > is the case, this is a specific "feature" of the qemu implementation. > > > > 2 - VIRTIO_F_PLATFORM_DMA (or whatever you want to call it), is a > > property of the guest platform itself (not qemu), there's no way the > > "peer" can advertize it via the virtio negociated flags. At least for > > us. I don't know for sure whether that would be workable for the ARM &gt...

...2018 at 10:24:57AM -0500, Benjamin Herrenschmidt wrote: > On Wed, 2018-08-01 at 01:36 -0700, Christoph Hellwig wrote: > > We just need to figure out how to deal with devices that deviate > > from the default. One things is that VIRTIO_F_IOMMU_PLATFORM really > > should become VIRTIO_F_PLATFORM_DMA to cover the cases of non-iommu > > dma tweaks (offsets, cache flushing), which seems well in spirit of > > the original design. > > I don't completely agree: > > 1 - VIRTIO_F_IOMMU_PLATFORM is a property of the "other side", ie qemu > for example. It ind...

On Fri, Jul 27, 2018 at 10:58:05AM +0100, Will Deacon wrote: > > I just wanted to say that this patch series provides a means for us to > force the coherent DMA ops for legacy virtio devices on arm64, which in turn > means that we can enable the SMMU with legacy devices in our fastmodel > emulation platform (which is slowly being upgraded to virtio 1.0) without > hanging during

On Fri, Jul 27, 2018 at 10:58:05AM +0100, Will Deacon wrote: > > I just wanted to say that this patch series provides a means for us to > force the coherent DMA ops for legacy virtio devices on arm64, which in turn > means that we can enable the SMMU with legacy devices in our fastmodel > emulation platform (which is slowly being upgraded to virtio 1.0) without > hanging during

...gt; > > for example. It indicates that the peer bypasses the normal platform > > > iommu. The platform code in the guest has no real way to know that this > > > is the case, this is a specific "feature" of the qemu implementation. > > > > > > 2 - VIRTIO_F_PLATFORM_DMA (or whatever you want to call it), is a > > > property of the guest platform itself (not qemu), there's no way the > > > "peer" can advertize it via the virtio negociated flags. At least for > > > us. I don't know for sure whether that would be workable...

...seems a shame not to support the current platform, especially given that other systems do have hacks in mainline to get virtio working. > We just need to figure out how to deal with devices that deviate > from the default. One things is that VIRTIO_F_IOMMU_PLATFORM really > should become VIRTIO_F_PLATFORM_DMA to cover the cases of non-iommu > dma tweaks (offsets, cache flushing), which seems well in spirit of > the original design. The other issue is VIRTIO_F_IO_BARRIER > which is very vaguely defined, and which needs a better definition. > And last but not least we'll need some text ex...

...ly on platform specific ways for this. To this end > there was a recent proposal to rename VIRTIO_F_IO_BARRIER to > VIRTIO_F_REAL_DEVICE. It got stuck since "real" sounds vague to people, > e.g. what if it's a VF - is that real or not? But I can see something > like e.g. VIRTIO_F_PLATFORM_DMA gaining support. > > We would then rename virtio_has_iommu_quirk to virtio_has_dma_quirk > and test VIRTIO_F_PLATFORM_DMA in addition to the IOMMU thing. I don't really care about the exact naming, and indeed a device that sets the flag doesn't have to be a 'real' device...

...ly on platform specific ways for this. To this end > there was a recent proposal to rename VIRTIO_F_IO_BARRIER to > VIRTIO_F_REAL_DEVICE. It got stuck since "real" sounds vague to people, > e.g. what if it's a VF - is that real or not? But I can see something > like e.g. VIRTIO_F_PLATFORM_DMA gaining support. > > We would then rename virtio_has_iommu_quirk to virtio_has_dma_quirk > and test VIRTIO_F_PLATFORM_DMA in addition to the IOMMU thing. I don't really care about the exact naming, and indeed a device that sets the flag doesn't have to be a 'real' device...

On Sun, 2018-08-05 at 00:29 -0700, Christoph Hellwig wrote: > On Sun, Aug 05, 2018 at 11:10:15AM +1000, Benjamin Herrenschmidt wrote: > > - One you have rejected, which is to have a way for "no-iommu" virtio > > (which still doesn't use an iommu on the qemu side and doesn't need > > to), to be forced to use some custom DMA ops on the VM side. > > >

On Sun, 2018-08-05 at 00:29 -0700, Christoph Hellwig wrote: > On Sun, Aug 05, 2018 at 11:10:15AM +1000, Benjamin Herrenschmidt wrote: > > - One you have rejected, which is to have a way for "no-iommu" virtio > > (which still doesn't use an iommu on the qemu side and doesn't need > > to), to be forced to use some custom DMA ops on the VM side. > > >

...r not rather than rely on platform specific ways for this. To this end there was a recent proposal to rename VIRTIO_F_IO_BARRIER to VIRTIO_F_REAL_DEVICE. It got stuck since "real" sounds vague to people, e.g. what if it's a VF - is that real or not? But I can see something like e.g. VIRTIO_F_PLATFORM_DMA gaining support. We would then rename virtio_has_iommu_quirk to virtio_has_dma_quirk and test VIRTIO_F_PLATFORM_DMA in addition to the IOMMU thing. -- MST

...ad and its previous iterations I think we need to stick to the current always physical, bypass system dma ops mode of virtio operation as the default. We just need to figure out how to deal with devices that deviate from the default. One things is that VIRTIO_F_IOMMU_PLATFORM really should become VIRTIO_F_PLATFORM_DMA to cover the cases of non-iommu dma tweaks (offsets, cache flushing), which seems well in spirit of the original design. The other issue is VIRTIO_F_IO_BARRIER which is very vaguely defined, and which needs a better definition. And last but not least we'll need some text explaining the challen...

...ehind an IOMMU that translates bus addresses from the device into physical addresses in memory. If this feature bit is set to 0, then the device emits physical addresses which are not translated further, even though an IOMMU may be present. And I'd change it to something like: VIRTIO_F_PLATFORM_DMA(33) This feature indicates that the device emits platform specific bus addresses that might not be identical to physical address. The translation of physical to bus address is platform speific and defined by the plaform specification for the bus that the virtio device is attache...

...fic ways for this. To this end > > there was a recent proposal to rename VIRTIO_F_IO_BARRIER to > > VIRTIO_F_REAL_DEVICE. It got stuck since "real" sounds vague to people, > > e.g. what if it's a VF - is that real or not? But I can see something > > like e.g. VIRTIO_F_PLATFORM_DMA gaining support. > > > > We would then rename virtio_has_iommu_quirk to virtio_has_dma_quirk > > and test VIRTIO_F_PLATFORM_DMA in addition to the IOMMU thing. > > I don't really care about the exact naming, and indeed a device that > sets the flag doesn't have...

...bus addresses from the device into physical addresses in > memory. If this feature bit is set to 0, then the device emits > physical addresses which are not translated further, even though an > IOMMU may be present. > > And I'd change it to something like: > > VIRTIO_F_PLATFORM_DMA(33) > This feature indicates that the device emits platform specific > bus addresses that might not be identical to physical address. > The translation of physical to bus address is platform speific > and defined by the plaform specification for the bus that the virtio &...