> -----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. > 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? > 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) Thanks -Bharat > > Alex > > > > It seems like you'd want to use your device to get a vfio group > > > reference, from which you could do something with the vfio external > > > user interface and get the iommu domain reference. Thanks, > > > > > > Alex > > > > > > > > > /* > > > > > > * IOMMU groups are really the natrual working unit of the IOMMU, but > > > > > > * the IOMMU API works on domains and devices. Bridge that > > > > > > gap by diff --git a/include/linux/iommu.h > > > > > > b/include/linux/iommu.h index 7ea319e..fa046bd 100644 > > > > > > --- a/include/linux/iommu.h > > > > > > +++ b/include/linux/iommu.h > > > > > > @@ -127,6 +127,7 @@ struct iommu_ops { > > > > > > int (*domain_set_windows)(struct iommu_domain *domain, u32 > > > w_count); > > > > > > /* Get the numer of window per domain */ > > > > > > u32 (*domain_get_windows)(struct iommu_domain *domain); > > > > > > + struct iommu_domain *(*get_dev_iommu_domain)(struct device > > > > > > +*dev); > > > > > > > > > > > > unsigned long pgsize_bitmap; }; @@ -190,6 +191,7 @@ extern > > > > > > int iommu_domain_window_enable(struct iommu_domain > > > > > *domain, u32 wnd_nr, > > > > > > phys_addr_t offset, u64 size, > > > > > > int prot); > > > > > > extern void iommu_domain_window_disable(struct iommu_domain > > > > > > *domain, > > > > > > u32 wnd_nr); > > > > > > +extern struct iommu_domain *iommu_get_dev_domain(struct > > > > > > +device *dev); > > > > > > /** > > > > > > * report_iommu_fault() - report about an IOMMU fault to the > > > > > > IOMMU > > > framework > > > > > > * @domain: the iommu domain where the fault has happened @@ > > > > > > -284,6 > > > > > > +286,11 @@ static inline void > > > > > > +iommu_domain_window_disable(struct > > > > > > iommu_domain *domain, { } > > > > > > > > > > > > +static inline struct iommu_domain > > > > > > +*iommu_get_dev_domain(struct device > > > > > > +*dev) { > > > > > > + return NULL; > > > > > > +} > > > > > > + > > > > > > static inline phys_addr_t iommu_iova_to_phys(struct > > > > > > iommu_domain *domain, dma_addr_t iova) { > > > > > > return 0; > > > > > > > > > > > > > > > > > > > > -- > > > > > To unsubscribe from this list: send the line "unsubscribe linux-pci" > > > > > in the body of a message to majordomo@xxxxxxxxxxxxxxx More > > > > > majordomo info at http://vger.kernel.org/majordomo-info.html > > > > > > > > > > > > > > > > > > ��.n��������+%������w��{.n�����{���"�)�� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
