Messages in this thread | | | Subject | Re: [PATCH v2 -mm 0/2] x86: per-device dma_mapping_ops | From | FUJITA Tomonori <> | Date | Mon, 26 May 2008 15:11:52 +0900 |
| |
On Mon, 26 May 2008 09:39:20 +0530 Amit Shah <amit.shah@qumranet.com> wrote:
> On Sunday 25 May 2008 12:50:11 Muli Ben-Yehuda wrote: > > On Thu, May 22, 2008 at 04:13:02PM +0530, Amit Shah wrote: > > > OK; this sounds helpful. the hook can make a hypercall and confirm > > > with the host kernel if the device in question is an assigned > > > physical device. If yes, we replace the dma_ops. Though, the > > > original intent of having stackable ops is that we might want to go > > > through the swiotlb in the guest even for an assigned device if the > > > guest dma addresses are not in the addressable range of the guest > > > chipset. > > > > > > > created (it works with hot plugging). It enables IOMMUs to set up an > > > > appropriate dma_mapping_ops per device. > > > > > > From what we've discussed so far, it looks like stackable dma ops will > > > definitely be needed. Does this patchset provide something that stacking > > > won't? > > > > Yes---this patchset let's you have a per-device dma-ops, whereas with > > stackable you only get global dma-ops. I think it's clear we need > > both, and I think per-device dma-ops are the first thing that's > > needed. Stacking can then be introduced on a per-device basis. > > When we would want stacking, we'll want it globally and not per-device, isn't > it? Or at least for devices on a particular bus. > > When an IOMMU driver registers itself, it should tell which devices it's > interested in (each device behind a bus or by enumerating each device it > cares for). This should take care of all the scenarios and we won't have the > need for per-device dma_ops.
Well, without per-device dma_ops, IOMMUs could live. But it's pretty hacky. Every time a dma operation is called, IOMMUs need to figure out how a device should be handled.
If IOMMUs can set dma_ops for the device when a new device is created, IOMMUs don't care anything any more. That's much clean. That's What the POWER architecture does.
> For something like pvdma, we can walk through the list of pci devices and make > a hypercall for each of them to get this information and have the pvdma > version of dma_ops registered for that device. This sounds like it's > per-device dma_ops, but it's not -- internally, the dma operations walk > through each of the IOMMUs registered and call them in sequence.
As Muli poinsted out, For pvdma, you need stacking per-device dma_ops. With per-device dma_ops, you don't need hack like adding is_pv_device hook in dma_ops. You can set your dma_ops to only pci devices that you are interested.
| |