> -----Original Message----- > From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx] > Sent: Friday, October 11, 2013 2:12 AM > To: Sethi Varun-B16395 > Cc: Bhushan Bharat-R65777; agraf@xxxxxxx; Wood Scott-B07421; linux- > pci@xxxxxxxxxxxxxxx; galak@xxxxxxxxxxxxxxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; > benh@xxxxxxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx > Subject: Re: [PATCH 2/7] iommu: add api to get iommu_domain of a device > > On Thu, 2013-10-10 at 20:09 +0000, Sethi Varun-B16395 wrote: > > > > > -----Original Message----- > > > From: iommu-bounces@xxxxxxxxxxxxxxxxxxxxxxxxxx [mailto:iommu- > > > bounces@xxxxxxxxxxxxxxxxxxxxxxxxxx] On Behalf Of Alex Williamson > > > Sent: Tuesday, October 08, 2013 8:43 AM > > > To: Bhushan Bharat-R65777 > > > Cc: agraf@xxxxxxx; Wood Scott-B07421; linux-pci@xxxxxxxxxxxxxxx; > > > galak@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > > > iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; benh@xxxxxxxxxxxxxxxxxxx; > > > linuxppc- dev@xxxxxxxxxxxxxxxx > > > Subject: Re: [PATCH 2/7] iommu: add api to get iommu_domain of a > > > device > > > > > > On Mon, 2013-10-07 at 05:46 +0000, Bhushan Bharat-R65777 wrote: > > > > > > > > > -----Original Message----- > > > > > From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx] > > > > > Sent: Friday, October 04, 2013 11:42 PM > > > > > To: Bhushan Bharat-R65777 > > > > > Cc: joro@xxxxxxxxxx; benh@xxxxxxxxxxxxxxxxxxx; > > > > > galak@xxxxxxxxxxxxxxxxxxx; linux- kernel@xxxxxxxxxxxxxxx; > > > > > linuxppc-dev@xxxxxxxxxxxxxxxx; linux- pci@xxxxxxxxxxxxxxx; > > > > > agraf@xxxxxxx; Wood Scott-B07421; iommu@lists.linux- > > > > > foundation.org > > > > > Subject: Re: [PATCH 2/7] iommu: add api to get iommu_domain of a > > > > > device > > > > > > > > > > On Fri, 2013-10-04 at 17:23 +0000, Bhushan Bharat-R65777 wrote: > > > > > > > > > > > > > -----Original Message----- > > > > > > > From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx] > > > > > > > Sent: Friday, October 04, 2013 10:43 PM > > > > > > > To: Bhushan Bharat-R65777 > > > > > > > Cc: joro@xxxxxxxxxx; benh@xxxxxxxxxxxxxxxxxxx; > > > > > > > galak@xxxxxxxxxxxxxxxxxxx; linux- kernel@xxxxxxxxxxxxxxx; > > > > > > > linuxppc-dev@xxxxxxxxxxxxxxxx; linux- pci@xxxxxxxxxxxxxxx; > > > > > > > agraf@xxxxxxx; Wood Scott-B07421; iommu@lists.linux- > > > > > > > foundation.org > > > > > > > Subject: Re: [PATCH 2/7] iommu: add api to get iommu_domain > > > > > > > of a device > > > > > > > > > > > > > > On Fri, 2013-10-04 at 16:47 +0000, Bhushan Bharat-R65777 > wrote: > > > > > > > > > > > > > > > > > -----Original Message----- > > > > > > > > > From: Alex Williamson > > > > > > > > > [mailto:alex.williamson@xxxxxxxxxx] > > > > > > > > > Sent: Friday, October 04, 2013 9:15 PM > > > > > > > > > To: Bhushan Bharat-R65777 > > > > > > > > > Cc: joro@xxxxxxxxxx; benh@xxxxxxxxxxxxxxxxxxx; > > > > > > > > > galak@xxxxxxxxxxxxxxxxxxx; linux- > > > > > > > > > kernel@xxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx; > > > > > > > > > linux- pci@xxxxxxxxxxxxxxx; agraf@xxxxxxx; Wood > > > > > > > > > Scott-B07421; iommu@lists.linux- foundation.org > > > > > > > > > Subject: Re: [PATCH 2/7] iommu: add api to get > > > > > > > > > iommu_domain of a device > > > > > > > > > > > > > > > > > > On Fri, 2013-10-04 at 09:54 +0000, Bhushan Bharat-R65777 > > > wrote: > > > > > > > > > > > > > > > > > > > > > -----Original Message----- > > > > > > > > > > > From: linux-pci-owner@xxxxxxxxxxxxxxx > > > > > > > > > > > [mailto:linux-pci-owner@xxxxxxxxxxxxxxx] > > > > > > > > > > > On Behalf Of Alex Williamson > > > > > > > > > > > Sent: Wednesday, September 25, 2013 10:16 PM > > > > > > > > > > > To: Bhushan Bharat-R65777 > > > > > > > > > > > Cc: joro@xxxxxxxxxx; benh@xxxxxxxxxxxxxxxxxxx; > > > > > > > > > > > galak@xxxxxxxxxxxxxxxxxxx; linux- > > > > > > > > > > > kernel@xxxxxxxxxxxxxxx; > > > > > > > > > > > linuxppc-dev@xxxxxxxxxxxxxxxx; > > > > > > > > > > > linux- pci@xxxxxxxxxxxxxxx; agraf@xxxxxxx; Wood > > > > > > > > > > > Scott-B07421; iommu@lists.linux- foundation.org; > > > > > > > > > > > Bhushan > > > > > > > > > > > Bharat-R65777 > > > > > > > > > > > Subject: Re: [PATCH 2/7] iommu: add api to get > > > > > > > > > > > iommu_domain of a device > > > > > > > > > > > > > > > > > > > > > > On Thu, 2013-09-19 at 12:59 +0530, Bharat Bhushan > wrote: > > > > > > > > > > > > This api return the iommu domain to which the > > > > > > > > > > > > device is > > > attached. > > > > > > > > > > > > The iommu_domain is required for making API calls > > > > > > > > > > > > related to > > > > > iommu. > > > > > > > > > > > > Follow up patches which use this API to know iommu > > > maping. > > > > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Bharat Bhushan > > > > > > > > > > > > <bharat.bhushan@xxxxxxxxxxxxx> > > > > > > > > > > > > --- > > > > > > > > > > > > drivers/iommu/iommu.c | 10 ++++++++++ > > > > > > > > > > > > include/linux/iommu.h | 7 +++++++ > > > > > > > > > > > > 2 files changed, 17 insertions(+), 0 deletions(-) > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/drivers/iommu/iommu.c > > > > > > > > > > > > b/drivers/iommu/iommu.c index > > > > > > > > > > > > fbe9ca7..6ac5f50 100644 > > > > > > > > > > > > --- a/drivers/iommu/iommu.c > > > > > > > > > > > > +++ b/drivers/iommu/iommu.c > > > > > > > > > > > > @@ -696,6 +696,16 @@ void > > > > > > > > > > > > iommu_detach_device(struct iommu_domain *domain, > > > > > > > > > > > > struct device *dev) } > > > > > > > > > > > > EXPORT_SYMBOL_GPL(iommu_detach_device); > > > > > > > > > > > > > > > > > > > > > > > > +struct iommu_domain *iommu_get_dev_domain(struct > > > device *dev) { > > > > > > > > > > > > + struct iommu_ops *ops = dev->bus->iommu_ops; > > > > > > > > > > > > + > > > > > > > > > > > > + if (unlikely(ops == NULL || > > > > > > > > > > > > +ops->get_dev_iommu_domain == > > > > > NULL)) > > > > > > > > > > > > + return NULL; > > > > > > > > > > > > + > > > > > > > > > > > > + return ops->get_dev_iommu_domain(dev); } > > > > > > > > > > > > +EXPORT_SYMBOL_GPL(iommu_get_dev_domain); > > > > > > > > > > > > > > > > > > > > > > What prevents this from racing iommu_domain_free()? > > > > > > > > > > > There's no references acquired, so there's no reason > > > > > > > > > > > for the caller to assume the > > > > > > > > > pointer is valid. > > > > > > > > > > > > > > > > > > > > Sorry for late query, somehow this email went into a > > > > > > > > > > folder and escaped; > > > > > > > > > > > > > > > > > > > > Just to be sure, there is not lock at generic "struct > > > > > > > > > > iommu_domain", but IP > > > > > > > > > specific structure (link FSL domain) linked in > > > > > > > > > iommu_domain->priv have a lock, so we need to ensure > > > > > > > > > this race in FSL iommu code (say > > > > > > > > > drivers/iommu/fsl_pamu_domain.c), > > > right? > > > > > > > > > > > > > > > > > > No, it's not sufficient to make sure that your use of > > > > > > > > > the interface is race free. The interface itself needs > > > > > > > > > to be designed so that it's difficult to use incorrectly. > > > > > > > > > > > > > > > > So we can define > > > > > > > > iommu_get_dev_domain()/iommu_put_dev_domain(); > > > > > > > > iommu_get_dev_domain() will return domain with the lock > > > > > > > > held, and > > > > > > > > iommu_put_dev_domain() will release the lock? And > > > > > > > > iommu_get_dev_domain() must always be followed by > > > > > > > > iommu_get_dev_domain(). > > > > > > > > > > > > > > What lock? get/put are generally used for reference > > > > > > > counting, not locking in the kernel. > > > > > > > > > > > > > > > > That's not the case here. This is a backdoor to get the > > > > > > > > > iommu domain from the iommu driver regardless of who is > > > > > > > > > using > > > it or how. > > > > > > > > > The iommu domain is created and managed by vfio, so > > > > > > > > > shouldn't we be looking at how to do this through vfio? > > > > > > > > > > > > > > > > Let me first describe what we are doing here: > > > > > > > > During initialization:- > > > > > > > > - vfio talks to MSI system to know the MSI-page and size > > > > > > > > - vfio then interacts with iommu to map the MSI-page in > > > > > > > > iommu (IOVA is decided by userspace and physical address > > > > > > > > is the > > > > > > > > MSI-page) > > > > > > > > - So the IOVA subwindow mapping is created in iommu and > > > > > > > > yes VFIO know about > > > > > > > this mapping. > > > > > > > > > > > > > > > > Now do SET_IRQ(MSI/MSIX) ioctl: > > > > > > > > - calls pci_enable_msix()/pci_enable_msi_block(): which > > > > > > > > is supposed to set > > > > > > > MSI address/data in device. > > > > > > > > - So in current implementation (this patchset) > > > > > > > > msi-subsystem gets the IOVA > > > > > > > from iommu via this defined interface. > > > > > > > > - Are you saying that rather than getting this from > > > > > > > > iommu, we should get this > > > > > > > from vfio? What difference does this make? > > > > > > > > > > > > > > Yes, you just said above that vfio knows the msi to iova > > > > > > > mapping, so why go outside of vfio to find it later? The > > > > > > > difference is one case you can have a proper reference to > > > > > > > data structures to make sure the pointer you get back > > > > > > > actually has meaning at the time you're using it vs the code > > > > > > > here where you're defining an API that returns a meaningless > > > > > > > value > > > > > > > > > > > > With FSL-PAMU we will always get consistant data from iommu or > > > > > > vfio-data > > > > > structure. > > > > > > > > > > Great, but you're trying to add a generic API to the IOMMU > > > > > subsystem that's difficult to use correctly. The fact that you > > > > > use it correctly does not justify the API. > > > > > > > > > > > > because you can't check or > > > > > > > enforce that an arbitrary caller is using it correctly. > > > > > > > > > > > > I am not sure what is arbitrary caller? pdev is known to vfio, > > > > > > so vfio will only make > > > > > > pci_enable_msix()/pci_enable_msi_block() for > > > this pdev. > > > > > > If anyother code makes then it is some other unexpectedly > > > > > > thing happening in system, no? > > > > > > > > > > What's proposed here is a generic IOMMU API. Anybody can call > this. > > > > > What if the host SCSI driver decides to go get the iommu domain > > > > > for it's device (or any other device)? Does that fit your usage > model? > > > > > > > > > > > > It's not maintainable. > > > > > > > Thanks, > > > > > > > > > > > > I do not have any issue with this as well, can you also > > > > > > describe the type of API you are envisioning; I can think of > > > > > > defining some function in vfio.c/vfio_iommu*.c, make them > > > > > > global and declare then in include/Linux/vfio.h And include > > > > > > <Linux/vfio.h> in caller file > > > > > > (arch/powerpc/kernel/msi.c) > > > > > > > > > > Do you really want module dependencies between vfio and your > > > > > core kernel MSI setup? Look at the vfio external user interface > > > > > that > > > we've already defined. > > > > > That allows other components of the kernel to get a proper > > > > > reference to a vfio group. From there you can work out how to > > > > > get what you want. Another alternative is that vfio could > > > > > register an MSI to IOVA mapping with architecture code when the > mapping is created. > > > > > The MSI setup path could then do a lookup in architecture code > > > > > for the mapping. You could even store the MSI to IOVA mapping > > > > > in VFIO and create an interface where SET_IRQ passes that > > > > > mapping into setup > > > code. > > [Sethi Varun-B16395] What you are suggesting is that the MSI setup > > path queries the vfio subsystem for the mapping, rather than directly > > querying the iommu subsystem. So, say if we add an interface for > > getting MSI to IOVA mapping in the msi setup path, wouldn't this again > > be specific to vfio? I reckon that this interface would again ppc > > machine specific interface. > > Sure, if this is a generic MSI setup path then clearly vfio should not be > involved. But by that same notion, if this is a generic MSI setup path, > how can the proposed solutions guarantee that the iommu_domain or iova > returned is still valid in all cases? It's racy. If the caller trying > to setup MSI has the information needed, why doesn't it pass it in as > part of the setup? Thanks, [Sethi Varun-B16395] Agreed, the proposed interface is not clean. But, we still need an interface through which MSI driver can call in to the vfio layer. -Varun ��.n��������+%������w��{.n�����{���"�)�� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
