Messages in this thread | | | Date | Wed, 22 Apr 2015 15:22:41 +1000 | From | David Gibson <> | Subject | Re: [PATCH kernel v8 14/31] vfio: powerpc/spapr: powerpc/powernv/ioda2: Rework IOMMU ownership control |
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On Tue, Apr 21, 2015 at 09:47:54PM +1000, Alexey Kardashevskiy wrote: > On 04/21/2015 07:43 PM, David Gibson wrote: > >On Mon, Apr 20, 2015 at 04:55:32PM +1000, Alexey Kardashevskiy wrote: > >>On 04/20/2015 12:44 PM, David Gibson wrote: > >>>On Fri, Apr 17, 2015 at 08:09:29PM +1000, Alexey Kardashevskiy wrote: > >>>>On 04/16/2015 04:07 PM, David Gibson wrote: > >>>>>On Fri, Apr 10, 2015 at 04:30:56PM +1000, Alexey Kardashevskiy wrote: > >>>>>>At the moment the iommu_table struct has a set_bypass() which enables/ > >>>>>>disables DMA bypass on IODA2 PHB. This is exposed to POWERPC IOMMU code > >>>>>>which calls this callback when external IOMMU users such as VFIO are > >>>>>>about to get over a PHB. > >>>>>> > >>>>>>The set_bypass() callback is not really an iommu_table function but > >>>>>>IOMMU/PE function. This introduces a iommu_table_group_ops struct and > >>>>>>adds a set_ownership() callback to it which is called when an external > >>>>>>user takes control over the IOMMU. > >>>>> > >>>>>Do you really need separate ops structures at both the single table > >>>>>and table group level? The different tables in a group will all > >>>>>belong to the same basic iommu won't they? > >>>> > >>>> > >>>>IOMMU tables exist alone in VIO. Also, the platform code uses just a table > >>>>(or it is in bypass mode) and does not care about table groups. It looked > >>>>more clean for myself to keep them separated. Should I still merge > >>>>those? > >>> > >>>Ok, that sounds like a reasonable argument for keeping them separate, > >>>at least for now. > >>> > >>>>>>This renames set_bypass() to set_ownership() as it is not necessarily > >>>>>>just enabling bypassing, it can be something else/more so let's give it > >>>>>>more generic name. The bool parameter is inverted. > >>>>>> > >>>>>>The callback is implemented for IODA2 only. Other platforms (P5IOC2, > >>>>>>IODA1) will use the old iommu_take_ownership/iommu_release_ownership API. > >>>>>> > >>>>>>Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru> > >>>>>>--- > >>>>>> arch/powerpc/include/asm/iommu.h | 14 +++++++++++++- > >>>>>> arch/powerpc/platforms/powernv/pci-ioda.c | 30 ++++++++++++++++++++++-------- > >>>>>> drivers/vfio/vfio_iommu_spapr_tce.c | 25 +++++++++++++++++++++---- > >>>>>> 3 files changed, 56 insertions(+), 13 deletions(-) > >>>>>> > >>>>>>diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h > >>>>>>index b9e50d3..d1f8c6c 100644 > >>>>>>--- a/arch/powerpc/include/asm/iommu.h > >>>>>>+++ b/arch/powerpc/include/asm/iommu.h > >>>>>>@@ -92,7 +92,6 @@ struct iommu_table { > >>>>>> unsigned long it_page_shift;/* table iommu page size */ > >>>>>> struct iommu_table_group *it_group; > >>>>>> struct iommu_table_ops *it_ops; > >>>>>>- void (*set_bypass)(struct iommu_table *tbl, bool enable); > >>>>>> }; > >>>>>> > >>>>>> /* Pure 2^n version of get_order */ > >>>>>>@@ -127,11 +126,24 @@ extern struct iommu_table *iommu_init_table(struct iommu_table * tbl, > >>>>>> > >>>>>> #define IOMMU_TABLE_GROUP_MAX_TABLES 1 > >>>>>> > >>>>>>+struct iommu_table_group; > >>>>>>+ > >>>>>>+struct iommu_table_group_ops { > >>>>>>+ /* > >>>>>>+ * Switches ownership from the kernel itself to an external > >>>>>>+ * user. While onwership is enabled, the kernel cannot use IOMMU > >>>>>>+ * for itself. > >>>>>>+ */ > >>>>>>+ void (*set_ownership)(struct iommu_table_group *table_group, > >>>>>>+ bool enable); > >>>>> > >>>>>The meaning of "enable" in a function called "set_ownership" is > >>>>>entirely obscure. > >>>> > >>>>Suggest something better please :) I have nothing better... > >>> > >>>Well, given it's "set_ownershuip" you could have "owner" - that would > >>>want to be an enum with OWNER_KERNEL and OWNER_VFIO or something > >>>rather than a bool. > >> > >> > >>It is iommu_take_ownership() in upstream and it is assumed that the owner is > >>anything but the platform code (for now and probably for ever - VFIO). I am > >>not changing this now, just using same naming approach when adding a > >>callback with a similar name. > > > >So "enabled" is actually that non kernel ownership is enabled. That > >is totally non-obvious. > > > >>>Or you could leave it a bool but call it "allow_bypass". > >> > >>Commented below. > >> > >>>>>>+}; > >>>>>>+ > >>>>>> struct iommu_table_group { > >>>>>> #ifdef CONFIG_IOMMU_API > >>>>>> struct iommu_group *group; > >>>>>> #endif > >>>>>> struct iommu_table tables[IOMMU_TABLE_GROUP_MAX_TABLES]; > >>>>>>+ struct iommu_table_group_ops *ops; > >>>>>> }; > >>>>>> > >>>>>> #ifdef CONFIG_IOMMU_API > >>>>>>diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c > >>>>>>index a964c50..9687731 100644 > >>>>>>--- a/arch/powerpc/platforms/powernv/pci-ioda.c > >>>>>>+++ b/arch/powerpc/platforms/powernv/pci-ioda.c > >>>>>>@@ -1255,10 +1255,8 @@ static void pnv_pci_ioda_setup_dma_pe(struct pnv_phb *phb, > >>>>>> __free_pages(tce_mem, get_order(TCE32_TABLE_SIZE * segs)); > >>>>>> } > >>>>>> > >>>>>>-static void pnv_pci_ioda2_set_bypass(struct iommu_table *tbl, bool enable) > >>>>>>+static void pnv_pci_ioda2_set_bypass(struct pnv_ioda_pe *pe, bool enable) > >>>>>> { > >>>>>>- struct pnv_ioda_pe *pe = container_of(tbl->it_group, struct pnv_ioda_pe, > >>>>>>- table_group); > >>>>>> uint16_t window_id = (pe->pe_number << 1 ) + 1; > >>>>>> int64_t rc; > >>>>>> > >>>>>>@@ -1286,7 +1284,8 @@ static void pnv_pci_ioda2_set_bypass(struct iommu_table *tbl, bool enable) > >>>>>> * host side. > >>>>>> */ > >>>>>> if (pe->pdev) > >>>>>>- set_iommu_table_base(&pe->pdev->dev, tbl); > >>>>>>+ set_iommu_table_base(&pe->pdev->dev, > >>>>>>+ &pe->table_group.tables[0]); > >>>>>> else > >>>>>> pnv_ioda_setup_bus_dma(pe, pe->pbus, false); > >>>>>> } > >>>>>>@@ -1302,13 +1301,27 @@ static void pnv_pci_ioda2_setup_bypass_pe(struct pnv_phb *phb, > >>>>>> /* TVE #1 is selected by PCI address bit 59 */ > >>>>>> pe->tce_bypass_base = 1ull << 59; > >>>>>> > >>>>>>- /* Install set_bypass callback for VFIO */ > >>>>>>- pe->table_group.tables[0].set_bypass = pnv_pci_ioda2_set_bypass; > >>>>>>- > >>>>>> /* Enable bypass by default */ > >>>>>>- pnv_pci_ioda2_set_bypass(&pe->table_group.tables[0], true); > >>>>>>+ pnv_pci_ioda2_set_bypass(pe, true); > >>>>>> } > >>>>>> > >>>>>>+static void pnv_ioda2_set_ownership(struct iommu_table_group *table_group, > >>>>>>+ bool enable) > >>>>>>+{ > >>>>>>+ struct pnv_ioda_pe *pe = container_of(table_group, struct pnv_ioda_pe, > >>>>>>+ table_group); > >>>>>>+ if (enable) > >>>>>>+ iommu_take_ownership(table_group); > >>>>>>+ else > >>>>>>+ iommu_release_ownership(table_group); > >>>>>>+ > >>>>>>+ pnv_pci_ioda2_set_bypass(pe, !enable); > >>>>>>+} > >>>>>>+ > >>>>>>+static struct iommu_table_group_ops pnv_pci_ioda2_ops = { > >>>>>>+ .set_ownership = pnv_ioda2_set_ownership, > >>>>>>+}; > >>>>>>+ > >>>>>> static void pnv_pci_ioda2_setup_dma_pe(struct pnv_phb *phb, > >>>>>> struct pnv_ioda_pe *pe) > >>>>>> { > >>>>>>@@ -1376,6 +1389,7 @@ static void pnv_pci_ioda2_setup_dma_pe(struct pnv_phb *phb, > >>>>>> } > >>>>>> tbl->it_ops = &pnv_iommu_ops; > >>>>>> iommu_init_table(tbl, phb->hose->node); > >>>>>>+ pe->table_group.ops = &pnv_pci_ioda2_ops; > >>>>>> iommu_register_group(&pe->table_group, phb->hose->global_number, > >>>>>> pe->pe_number); > >>>>>> > >>>>>>diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c > >>>>>>index 9f38351..d5d8c50 100644 > >>>>>>--- a/drivers/vfio/vfio_iommu_spapr_tce.c > >>>>>>+++ b/drivers/vfio/vfio_iommu_spapr_tce.c > >>>>>>@@ -535,9 +535,22 @@ static int tce_iommu_attach_group(void *iommu_data, > >>>>>> goto unlock_exit; > >>>>>> } > >>>>>> > >>>>>>- ret = iommu_take_ownership(table_group); > >>>>>>- if (!ret) > >>>>>>- container->grp = iommu_group; > >>>>>>+ if (!table_group->ops || !table_group->ops->set_ownership) { > >>>>>>+ ret = iommu_take_ownership(table_group); > >>>>>>+ } else { > >>>>>>+ /* > >>>>>>+ * Disable iommu bypass, otherwise the user can DMA to all of > >>>>>>+ * our physical memory via the bypass window instead of just > >>>>>>+ * the pages that has been explicitly mapped into the iommu > >>>>>>+ */ > >>>>>>+ table_group->ops->set_ownership(table_group, true); > >>>>> > >>>>>And here to disable bypass you call it with enable=true, so it doesn't > >>>>>even have the same meaning as it used to. > >>>> > >>>> > >>>>I do not disable bypass per se (even if it what set_ownership(true) does) as > >>>>it is IODA business and VFIO has no idea about it. I do take control over > >>>>the group. I am not following you here - what used to have the same > >>>>meaning? > >>> > >>>Well, in set_bypass, the enable parameter was whether bypass was > >>>enabled. Here you're setting enable to true, when you want to > >>>*disable* bypass (in the existing case). If the "enable" parameter > >>>isn't about enabling bypass, it's meaning is even more confusing than > >>>I thought. > >> > >> > >>Its meaning is "take ownership over the group". In this patch > >>set_ownership(true) means set_bypass(false). > > > >Ok. So "take_ownership" isn't quite as clear as I'd like, but it's > >not too bad because it's implied that it's the caller that's taking > >the ownership. *set* ownership makes no sense without saying who the > >new owner is. "enable" has no clear meaning in that context. > > > >Calling it "kernel_owned" or "non_kernel_owned" would be ok if a bit > >clunky. > > > Strictly speaking VFIO and platform code are both kernel.
Well, true, but VFIO is generally holding the device on behalf of a userspace process or guest.
> So which one to choose? > > +struct iommu_table_group_ops { > + void (*take_ownership)(struct iommu_table_group *table_group); > + void (*release_ownership)(struct iommu_table_group *table_group); > +}; > > > OR > > +enum { IOMMU_TABLE_GROUP_OWNER_KERNEL, IOMMU_TABLE_GROUP_OWNER_VFIO }; > +struct iommu_table_group_ops { > + void (*set_ownership)(struct iommu_table_group *table_group, > + long owner); > +}; > > > I have bad taste for names like this, need a hint here, please :)
I think I'd be ok with either.
I think I'd vote for the first option, for consistency with the existing function names. If that requires a bunch of code duplication in the implementations between take and release, I'd probably change my mind though.
-- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson [unhandled content-type:application/pgp-signature] | |