Re: [PATCH kernel v9 13/32] vfio: powerpc/spapr/iommu/powernv/ioda2: Rework IOMMU ownership control

David Gibson
2015-04-30T04:38:43Z

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On Wed, Apr 29, 2015 at 07:19:51PM +1000, Alexey Kardashevskiy wrote:
> On 04/29/2015 01:02 PM, David Gibson wrote:
> >On Sat, Apr 25, 2015 at 10:14:37PM +1000, Alexey Kardashevskiy wrote:
> >>This adds tce_iommu_take_ownership() and tce_iommu_release_ownership
> >>which call in a loop iommu_take_ownership()/iommu_release_ownership()
> >>for every table on the group. As there is just one now, no change in
> >>behaviour is expected.
> >>
> >>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 take_ownership()/release_ownership() callbacks to it which are
> >>called when an external user takes/releases control over the IOMMU.
> >>
> >>This replaces set_bypass() with ownership callbacks as it is not
> >>necessarily just bypass enabling, it can be something else/more
> >>so let's give it more generic name.
> >>
> >>The callbacks is implemented for IODA2 only. Other platforms (P5IOC2,
> >>IODA1) will use the old iommu_take_ownership/iommu_release_ownership API.
> >>The following patches will replace iommu_take_ownership/
> >>iommu_release_ownership calls in IODA2 with full IOMMU table release/
> >>create.
> >>
> >>Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> >>[aw: for the vfio related changes]
> >>Acked-by: Alex Williamson <alex.williamson@redhat.com>
> >>---
> >>Changes:
> >>v9:
> >>* squashed "vfio: powerpc/spapr: powerpc/iommu: Rework IOMMU ownership control"
> >>and "vfio: powerpc/spapr: powerpc/powernv/ioda2: Rework IOMMU ownership control"
> >>into a single patch
> >>* moved helpers with a loop through tables in a group
> >>to vfio_iommu_spapr_tce.c to keep the platform code free of IOMMU table
> >>groups as much as possible
> >>* added missing tce_iommu_clear() to tce_iommu_release_ownership()
> >>* replaced the set_ownership(enable) callback with take_ownership() and
> >>release_ownership()
> >>---
> >> arch/powerpc/include/asm/iommu.h | 13 +++++-
> >> arch/powerpc/kernel/iommu.c | 11 ------
> >> arch/powerpc/platforms/powernv/pci-ioda.c | 40 +++++++++++++++----
> >> drivers/vfio/vfio_iommu_spapr_tce.c | 66 +++++++++++++++++++++++++++----
> >> 4 files changed, 103 insertions(+), 27 deletions(-)
> >>
> >>diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
> >>index fa37519..e63419e 100644
> >>--- a/arch/powerpc/include/asm/iommu.h
> >>+++ b/arch/powerpc/include/asm/iommu.h
> >>@@ -93,7 +93,6 @@ struct iommu_table {
> >> unsigned long it_page_shift;/* table iommu page size */
> >> struct iommu_table_group *it_table_group;
> >> struct iommu_table_ops *it_ops;
> >>- void (*set_bypass)(struct iommu_table *tbl, bool enable);
> >> };
> >>
> >> /* Pure 2^n version of get_order */
> >>@@ -128,11 +127,23 @@ 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 taken, the kernel cannot use IOMMU itself.
> >
> >Typo in "onwership". I'd also like to see this be even more explicit
> >that "take" is the "core kernel -> vfio/whatever" transition and
> >release is the reverse.
>
>
> Will this work?
>
> /*
> * Switches ownership from the kernel itself to an external
> * user.
> * The ownership is taken when VFIO starts using the IOMMU group
> * and released when the platform code gets the control over the group back.
> * While ownership is taken, the platform code cannot use IOMMU itself.
> */

Hrm, verbose and still doesn't emphasise the point that always
confuses me enough. I'd prefer:

/* Switch ownership from platform code to external user (e.g. VFIO) */

above "take" then

/* Switch ownership from external user (e.g. VFIO) back to core */

above "release"..

>
>
> >>+ */
> >>+ void (*take_ownership)(struct iommu_table_group *table_group);
> >>+ void (*release_ownership)(struct iommu_table_group *table_group);
> >>+};
> >>+
> >> 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/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
> >>index 005146b..2856d27 100644
> >>--- a/arch/powerpc/kernel/iommu.c
> >>+++ b/arch/powerpc/kernel/iommu.c
> >>@@ -1057,13 +1057,6 @@ int iommu_take_ownership(struct iommu_table *tbl)
> >>
> >> memset(tbl->it_map, 0xff, sz);
> >>
> >>- /*
> >>- * 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
> >>- */
> >>- if (tbl->set_bypass)
> >>- tbl->set_bypass(tbl, false);
> >>
> >> return 0;
> >> }
> >>@@ -1078,10 +1071,6 @@ void iommu_release_ownership(struct iommu_table *tbl)
> >> /* Restore bit#0 set by iommu_init_table() */
> >> if (tbl->it_offset == 0)
> >> set_bit(0, tbl->it_map);
> >>-
> >>- /* The kernel owns the device now, we can restore the iommu bypass */
> >>- if (tbl->set_bypass)
> >>- tbl->set_bypass(tbl, true);
> >> }
> >> EXPORT_SYMBOL_GPL(iommu_release_ownership);
> >>
> >>diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> >>index 88472cb..718d5cc 100644
> >>--- a/arch/powerpc/platforms/powernv/pci-ioda.c
> >>+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> >>@@ -1870,10 +1870,8 @@ 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_table_group,
> >>- struct pnv_ioda_pe, table_group);
> >> uint16_t window_id = (pe->pe_number << 1 ) + 1;
> >> int64_t rc;
> >>
> >>@@ -1901,7 +1899,8 @@ 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);
> >> }
> >>@@ -1917,13 +1916,35 @@ 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);
> >> }
> >>
> >>+#ifdef CONFIG_IOMMU_API
> >>+static void pnv_ioda2_take_ownership(struct iommu_table_group *table_group)
> >>+{
> >>+ struct pnv_ioda_pe *pe = container_of(table_group, struct pnv_ioda_pe,
> >>+ table_group);
> >>+
> >>+ iommu_take_ownership(&table_group->tables[0]);
> >>+ pnv_pci_ioda2_set_bypass(pe, false);
> >>+}
> >>+
> >>+static void pnv_ioda2_release_ownership(struct iommu_table_group *table_group)
> >>+{
> >>+ struct pnv_ioda_pe *pe = container_of(table_group, struct pnv_ioda_pe,
> >>+ table_group);
> >>+
> >>+ iommu_release_ownership(&table_group->tables[0]);
> >>+ pnv_pci_ioda2_set_bypass(pe, true);
> >>+}
> >>+
> >>+static struct iommu_table_group_ops pnv_pci_ioda2_ops = {
> >>+ .take_ownership = pnv_ioda2_take_ownership,
> >>+ .release_ownership = pnv_ioda2_release_ownership,
> >>+};
> >>+#endif
> >>+
> >> static void pnv_pci_ioda2_setup_dma_pe(struct pnv_phb *phb,
> >> struct pnv_ioda_pe *pe)
> >> {
> >>@@ -1991,6 +2012,9 @@ static void pnv_pci_ioda2_setup_dma_pe(struct pnv_phb *phb,
> >> }
> >> tbl->it_ops = &pnv_ioda2_iommu_ops;
> >> iommu_init_table(tbl, phb->hose->node);
> >>+#ifdef CONFIG_IOMMU_API
> >>+ pe->table_group.ops = &pnv_pci_ioda2_ops;
> >>+#endif
> >>
> >> if (pe->flags & PNV_IODA_PE_DEV) {
> >> iommu_register_group(&pe->table_group, phb->hose->global_number,
> >>diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> >>index 17e884a..dacc738 100644
> >>--- a/drivers/vfio/vfio_iommu_spapr_tce.c
> >>+++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> >>@@ -483,6 +483,43 @@ static long tce_iommu_ioctl(void *iommu_data,
> >> return -ENOTTY;
> >> }
> >>
> >>+static void tce_iommu_release_ownership(struct tce_container *container,
> >>+ struct iommu_table_group *table_group)
> >>+{
> >>+ int i;
> >>+
> >>+ for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i) {
> >>+ struct iommu_table *tbl = &table_group->tables[i];
> >>+
> >>+ tce_iommu_clear(container, tbl, tbl->it_offset, tbl->it_size);
> >>+ if (tbl->it_map)
> >>+ iommu_release_ownership(tbl);
> >>+ }
> >>+}
> >>+
> >>+static int tce_iommu_take_ownership(struct iommu_table_group *table_group)
> >>+{
> >>+ int i, j, rc = 0;
> >>+
> >>+ for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i) {
> >>+ struct iommu_table *tbl = &table_group->tables[i];
> >>+
> >>+ if (!tbl->it_map)
> >>+ continue;
> >>+
> >>+ rc = iommu_take_ownership(tbl);
> >>+ if (rc) {
> >>+ for (j = 0; j < i; ++j)
> >>+ iommu_release_ownership(
> >>+ &table_group->tables[j]);
> >>+
> >>+ return rc;
> >>+ }
> >>+ }
> >>+
> >>+ return 0;
> >>+}
> >>+
> >> static int tce_iommu_attach_group(void *iommu_data,
> >> struct iommu_group *iommu_group)
> >> {
> >>@@ -515,9 +552,23 @@ static int tce_iommu_attach_group(void *iommu_data,
> >> goto unlock_exit;
> >> }
> >>
> >>- ret = iommu_take_ownership(&table_group->tables[0]);
> >>- if (!ret)
> >>- container->grp = iommu_group;
> >>+ if (!table_group->ops || !table_group->ops->take_ownership ||
> >>+ !table_group->ops->release_ownership) {
> >>+ ret = tce_iommu_take_ownership(table_group);
> >
> >Haven't looked at the rest of the series. I'm hoping that you're
> >eventually planning to replace this fallback with setting the
> >take_ownership call for p5ioc etc. to point to
> >tce_iommu_take_ownership.
>
>
> Why? I do not really want p5ioc2 or ioda1 to have
> take_ownership/release_ownership callbacks defined as they will only do this
> default stuff which is not going to change ever as this hardware is quite
> old and extremely rare so there is no real customer for it. Should I still
> convert these to callbacks?

Leave it for now - having this fallback makes more sense in light of
the changes later in the series that I hadn't read when I made the
comment.

--
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

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