Re: [PATCH kernel v8 17/31] powerpc/iommu/powernv: Release replaced TCE

From: David Gibson
Date: Mon Apr 20 2015 - 02:03:15 EST

Next message: David Gibson: "Re: [PATCH kernel v8 12/31] powerpc/spapr: vfio: Switch from iommu_table to new iommu_table_group"
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In reply to: Alexey Kardashevskiy: "Re: [PATCH kernel v8 17/31] powerpc/iommu/powernv: Release replaced TCE"
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On Fri, Apr 17, 2015 at 08:37:54PM +1000, Alexey Kardashevskiy wrote:
> On 04/16/2015 04:26 PM, David Gibson wrote:
> >On Fri, Apr 10, 2015 at 04:30:59PM +1000, Alexey Kardashevskiy wrote:
> >>At the moment writing new TCE value to the IOMMU table fails with EBUSY
> >>if there is a valid entry already. However PAPR specification allows
> >>the guest to write new TCE value without clearing it first.
> >>
> >>Another problem this patch is addressing is the use of pool locks for
> >>external IOMMU users such as VFIO. The pool locks are to protect
> >>DMA page allocator rather than entries and since the host kernel does
> >>not control what pages are in use, there is no point in pool locks and
> >>exchange()+put_page(oldtce) is sufficient to avoid possible races.
> >>
> >>This adds an exchange() callback to iommu_table_ops which does the same
> >>thing as set() plus it returns replaced TCE and DMA direction so
> >>the caller can release the pages afterwards.
> >>
> >>The returned old TCE value is a virtual address as the new TCE value.
> >>This is different from tce_clear() which returns a physical address.
> >>
> >>This implements exchange() for P5IOC2/IODA/IODA2. This adds a requirement
> >>for a platform to have exchange() implemented in order to support VFIO.
> >>
> >>This replaces iommu_tce_build() and iommu_clear_tce() with
> >>a single iommu_tce_xchg().
> >>
> >>This makes sure that TCE permission bits are not set in TCE passed to
> >>IOMMU API as those are to be calculated by platform code from DMA direction.
> >>
> >>This moves SetPageDirty() to the IOMMU code to make it work for both
> >>VFIO ioctl interface in in-kernel TCE acceleration (when it becomes
> >>available later).
> >>
> >>Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
> >>---
> >> arch/powerpc/include/asm/iommu.h | 17 ++++++--
> >> arch/powerpc/kernel/iommu.c | 53 +++++++++---------------
> >> arch/powerpc/platforms/powernv/pci-ioda.c | 38 ++++++++++++++++++
> >> arch/powerpc/platforms/powernv/pci-p5ioc2.c | 3 ++
> >> arch/powerpc/platforms/powernv/pci.c | 17 ++++++++
> >> arch/powerpc/platforms/powernv/pci.h | 2 +
> >> drivers/vfio/vfio_iommu_spapr_tce.c | 62 ++++++++++++++++++-----------
> >> 7 files changed, 130 insertions(+), 62 deletions(-)
> >>
> >>diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
> >>index d1f8c6c..bde7ee7 100644
> >>--- a/arch/powerpc/include/asm/iommu.h
> >>+++ b/arch/powerpc/include/asm/iommu.h
> >>@@ -44,11 +44,22 @@ extern int iommu_is_off;
> >> extern int iommu_force_on;
> >>
> >> struct iommu_table_ops {
> >>+ /* When called with direction==DMA_NONE, it is equal to clear() */
> >> int (*set)(struct iommu_table *tbl,
> >> long index, long npages,
> >> unsigned long uaddr,
> >> enum dma_data_direction direction,
> >> struct dma_attrs *attrs);
> >>+#ifdef CONFIG_IOMMU_API
> >>+ /*
> >>+ * Exchanges existing TCE with new TCE plus direction bits;
> >>+ * returns old TCE and DMA direction mask
> >>+ */
> >>+ int (*exchange)(struct iommu_table *tbl,
> >>+ long index,
> >>+ unsigned long *tce,
> >>+ enum dma_data_direction *direction);
> >>+#endif
> >> void (*clear)(struct iommu_table *tbl,
> >> long index, long npages);
> >> unsigned long (*get)(struct iommu_table *tbl, long index);
> >>@@ -152,6 +163,8 @@ extern void iommu_register_group(struct iommu_table_group *table_group,
> >> extern int iommu_add_device(struct device *dev);
> >> extern void iommu_del_device(struct device *dev);
> >> extern int __init tce_iommu_bus_notifier_init(void);
> >>+extern long iommu_tce_xchg(struct iommu_table *tbl, unsigned long entry,
> >>+ unsigned long *tce, enum dma_data_direction *direction);
> >> #else
> >> static inline void iommu_register_group(struct iommu_table_group *table_group,
> >> int pci_domain_number,
> >>@@ -231,10 +244,6 @@ extern int iommu_tce_clear_param_check(struct iommu_table *tbl,
> >> unsigned long npages);
> >> extern int iommu_tce_put_param_check(struct iommu_table *tbl,
> >> unsigned long ioba, unsigned long tce);
> >>-extern int iommu_tce_build(struct iommu_table *tbl, unsigned long entry,
> >>- unsigned long hwaddr, enum dma_data_direction direction);
> >>-extern unsigned long iommu_clear_tce(struct iommu_table *tbl,
> >>- unsigned long entry);
> >>
> >> extern void iommu_flush_tce(struct iommu_table *tbl);
> >> extern int iommu_take_ownership(struct iommu_table_group *table_group);
> >>diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
> >>index 068fe4ff..501e8ee 100644
> >>--- a/arch/powerpc/kernel/iommu.c
> >>+++ b/arch/powerpc/kernel/iommu.c
> >>@@ -982,9 +982,6 @@ EXPORT_SYMBOL_GPL(iommu_tce_clear_param_check);
> >> int iommu_tce_put_param_check(struct iommu_table *tbl,
> >> unsigned long ioba, unsigned long tce)
> >> {
> >>- if (!(tce & (TCE_PCI_WRITE | TCE_PCI_READ)))
> >>- return -EINVAL;
> >>-
> >> if (tce & ~(IOMMU_PAGE_MASK(tbl) | TCE_PCI_WRITE | TCE_PCI_READ))
> >> return -EINVAL;
> >>
> >>@@ -1002,44 +999,20 @@ int iommu_tce_put_param_check(struct iommu_table *tbl,
> >> }
> >> EXPORT_SYMBOL_GPL(iommu_tce_put_param_check);
> >>
> >>-unsigned long iommu_clear_tce(struct iommu_table *tbl, unsigned long entry)
> >>-{
> >>- unsigned long oldtce;
> >>- struct iommu_pool *pool = get_pool(tbl, entry);
> >>-
> >>- spin_lock(&(pool->lock));
> >>-
> >>- oldtce = tbl->it_ops->get(tbl, entry);
> >>- if (oldtce & (TCE_PCI_WRITE | TCE_PCI_READ))
> >>- tbl->it_ops->clear(tbl, entry, 1);
> >>- else
> >>- oldtce = 0;
> >>-
> >>- spin_unlock(&(pool->lock));
> >>-
> >>- return oldtce;
> >>-}
> >>-EXPORT_SYMBOL_GPL(iommu_clear_tce);
> >>-
> >> /*
> >> * hwaddr is a kernel virtual address here (0xc... bazillion),
> >> * tce_build converts it to a physical address.
> >> */
> >>-int iommu_tce_build(struct iommu_table *tbl, unsigned long entry,
> >>- unsigned long hwaddr, enum dma_data_direction direction)
> >>+long iommu_tce_xchg(struct iommu_table *tbl, unsigned long entry,
> >>+ unsigned long *tce, enum dma_data_direction *direction)
> >> {
> >>- int ret = -EBUSY;
> >>- unsigned long oldtce;
> >>- struct iommu_pool *pool = get_pool(tbl, entry);
> >>+ long ret;
> >>
> >>- spin_lock(&(pool->lock));
> >>+ ret = tbl->it_ops->exchange(tbl, entry, tce, direction);
> >>
> >>- oldtce = tbl->it_ops->get(tbl, entry);
> >>- /* Add new entry if it is not busy */
> >>- if (!(oldtce & (TCE_PCI_WRITE | TCE_PCI_READ)))
> >>- ret = tbl->it_ops->set(tbl, entry, 1, hwaddr, direction, NULL);
> >>-
> >>- spin_unlock(&(pool->lock));
> >>+ if (!ret && ((*direction == DMA_FROM_DEVICE) ||
> >>+ (*direction == DMA_BIDIRECTIONAL)))
> >>+ SetPageDirty(pfn_to_page(__pa(*tce) >> PAGE_SHIFT));
> >>
> >> /* if (unlikely(ret))
> >> pr_err("iommu_tce: %s failed on hwaddr=%lx ioba=%lx kva=%lx ret=%d\n",
> >>@@ -1048,13 +1021,23 @@ int iommu_tce_build(struct iommu_table *tbl, unsigned long entry,
> >>
> >> return ret;
> >> }
> >>-EXPORT_SYMBOL_GPL(iommu_tce_build);
> >>+EXPORT_SYMBOL_GPL(iommu_tce_xchg);
> >>
> >> static int iommu_table_take_ownership(struct iommu_table *tbl)
> >> {
> >> unsigned long flags, i, sz = (tbl->it_size + 7) >> 3;
> >> int ret = 0;
> >>
> >>+ /*
> >>+ * VFIO does not control TCE entries allocation and the guest
> >>+ * can write new TCEs on top of existing ones so iommu_tce_build()
> >>+ * must be able to release old pages. This functionality
> >>+ * requires exchange() callback defined so if it is not
> >>+ * implemented, we disallow taking ownership over the table.
> >>+ */
> >>+ if (!tbl->it_ops->exchange)
> >>+ return -EINVAL;
> >>+
> >> spin_lock_irqsave(&tbl->large_pool.lock, flags);
> >> for (i = 0; i < tbl->nr_pools; i++)
> >> spin_lock(&tbl->pools[i].lock);
> >>diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> >>index fd993bc..4d80502 100644
> >>--- a/arch/powerpc/platforms/powernv/pci-ioda.c
> >>+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> >>@@ -1128,6 +1128,20 @@ static int pnv_ioda1_tce_build_vm(struct iommu_table *tbl, long index,
> >> return ret;
> >> }
> >>
> >>+#ifdef CONFIG_IOMMU_API
> >>+static int pnv_ioda1_tce_xchg_vm(struct iommu_table *tbl, long index,
> >>+ unsigned long *tce, enum dma_data_direction *direction)
> >>+{
> >>+ long ret = pnv_tce_xchg(tbl, index, tce, direction);
> >>+
> >>+ if (!ret && (tbl->it_type &
> >>+ (TCE_PCI_SWINV_CREATE | TCE_PCI_SWINV_FREE)))
> >>+ pnv_pci_ioda1_tce_invalidate(tbl, index, 1, false);
> >>+
> >>+ return ret;
> >>+}
> >>+#endif
> >>+
> >> static void pnv_ioda1_tce_free_vm(struct iommu_table *tbl, long index,
> >> long npages)
> >> {
> >>@@ -1139,6 +1153,9 @@ static void pnv_ioda1_tce_free_vm(struct iommu_table *tbl, long index,
> >>
> >> struct iommu_table_ops pnv_ioda1_iommu_ops = {
> >> .set = pnv_ioda1_tce_build_vm,
> >>+#ifdef CONFIG_IOMMU_API
> >>+ .exchange = pnv_ioda1_tce_xchg_vm,
> >>+#endif
> >> .clear = pnv_ioda1_tce_free_vm,
> >> .get = pnv_tce_get,
> >> };
> >>@@ -1190,6 +1207,20 @@ static int pnv_ioda2_tce_build_vm(struct iommu_table *tbl, long index,
> >> return ret;
> >> }
> >>
> >>+#ifdef CONFIG_IOMMU_API
> >>+static int pnv_ioda2_tce_xchg_vm(struct iommu_table *tbl, long index,
> >>+ unsigned long *tce, enum dma_data_direction *direction)
> >>+{
> >>+ long ret = pnv_tce_xchg(tbl, index, tce, direction);
> >>+
> >>+ if (!ret && (tbl->it_type &
> >>+ (TCE_PCI_SWINV_CREATE | TCE_PCI_SWINV_FREE)))
> >>+ pnv_pci_ioda2_tce_invalidate(tbl, index, 1, false);
> >>+
> >>+ return ret;
> >>+}
> >>+#endif
> >>+
> >> static void pnv_ioda2_tce_free_vm(struct iommu_table *tbl, long index,
> >> long npages)
> >> {
> >>@@ -1201,6 +1232,9 @@ static void pnv_ioda2_tce_free_vm(struct iommu_table *tbl, long index,
> >>
> >> static struct iommu_table_ops pnv_ioda2_iommu_ops = {
> >> .set = pnv_ioda2_tce_build_vm,
> >>+#ifdef CONFIG_IOMMU_API
> >>+ .exchange = pnv_ioda2_tce_xchg_vm,
> >>+#endif
> >> .clear = pnv_ioda2_tce_free_vm,
> >> .get = pnv_tce_get,
> >> };
> >>@@ -1353,6 +1387,7 @@ static void pnv_pci_ioda2_setup_bypass_pe(struct pnv_phb *phb,
> >> pnv_pci_ioda2_set_bypass(pe, true);
> >> }
> >>
> >>+#ifdef CONFIG_IOMMU_API
> >> static void pnv_ioda2_set_ownership(struct iommu_table_group *table_group,
> >> bool enable)
> >> {
> >>@@ -1369,6 +1404,7 @@ static void pnv_ioda2_set_ownership(struct iommu_table_group *table_group,
> >> static struct iommu_table_group_ops pnv_pci_ioda2_ops = {
> >> .set_ownership = pnv_ioda2_set_ownership,
> >> };
> >>+#endif
> >>
> >> static void pnv_pci_ioda2_setup_dma_pe(struct pnv_phb *phb,
> >> struct pnv_ioda_pe *pe)
> >>@@ -1437,7 +1473,9 @@ 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
> >> iommu_register_group(&pe->table_group, phb->hose->global_number,
> >> pe->pe_number);
> >>
> >>diff --git a/arch/powerpc/platforms/powernv/pci-p5ioc2.c b/arch/powerpc/platforms/powernv/pci-p5ioc2.c
> >>index 6906a9c..d2d9092 100644
> >>--- a/arch/powerpc/platforms/powernv/pci-p5ioc2.c
> >>+++ b/arch/powerpc/platforms/powernv/pci-p5ioc2.c
> >>@@ -85,6 +85,9 @@ static void pnv_pci_init_p5ioc2_msis(struct pnv_phb *phb) { }
> >>
> >> static struct iommu_table_ops pnv_p5ioc2_iommu_ops = {
> >> .set = pnv_tce_build,
> >>+#ifdef CONFIG_IOMMU_API
> >>+ .exchange = pnv_tce_xchg,
> >>+#endif
> >> .clear = pnv_tce_free,
> >> .get = pnv_tce_get,
> >> };
> >>diff --git a/arch/powerpc/platforms/powernv/pci.c b/arch/powerpc/platforms/powernv/pci.c
> >>index a8c05de..a9797dd 100644
> >>--- a/arch/powerpc/platforms/powernv/pci.c
> >>+++ b/arch/powerpc/platforms/powernv/pci.c
> >>@@ -615,6 +615,23 @@ int pnv_tce_build(struct iommu_table *tbl, long index, long npages,
> >> return 0;
> >> }
> >>
> >>+#ifdef CONFIG_IOMMU_API
> >>+int pnv_tce_xchg(struct iommu_table *tbl, long index,
> >>+ unsigned long *tce, enum dma_data_direction *direction)
> >>+{
> >>+ u64 proto_tce = iommu_direction_to_tce_perm(*direction);
> >>+ unsigned long newtce = __pa(*tce) | proto_tce;
> >>+ unsigned long idx = index - tbl->it_offset;
> >>+
> >>+ *tce = xchg(pnv_tce(tbl, idx), cpu_to_be64(newtce));
> >>+ *tce = (unsigned long) __va(be64_to_cpu(*tce));
> >>+ *direction = iommu_tce_direction(*tce);
> >>+ *tce &= ~(TCE_PCI_READ | TCE_PCI_WRITE);
> >>+
> >>+ return 0;
> >>+}
> >>+#endif
> >>+
> >> void pnv_tce_free(struct iommu_table *tbl, long index, long npages)
> >> {
> >> long i;
> >>diff --git a/arch/powerpc/platforms/powernv/pci.h b/arch/powerpc/platforms/powernv/pci.h
> >>index 0d4df32..4d1a78c 100644
> >>--- a/arch/powerpc/platforms/powernv/pci.h
> >>+++ b/arch/powerpc/platforms/powernv/pci.h
> >>@@ -220,6 +220,8 @@ extern int pnv_tce_build(struct iommu_table *tbl, long index, long npages,
> >> unsigned long uaddr, enum dma_data_direction direction,
> >> struct dma_attrs *attrs);
> >> extern void pnv_tce_free(struct iommu_table *tbl, long index, long npages);
> >>+extern int pnv_tce_xchg(struct iommu_table *tbl, long index,
> >>+ unsigned long *tce, enum dma_data_direction *direction);
> >> extern unsigned long pnv_tce_get(struct iommu_table *tbl, long index);
> >> extern struct iommu_table_ops pnv_ioda1_iommu_ops;
> >>
> >>diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> >>index d5d8c50..7c3c215 100644
> >>--- a/drivers/vfio/vfio_iommu_spapr_tce.c
> >>+++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> >>@@ -251,9 +251,6 @@ static void tce_iommu_unuse_page(struct tce_container *container,
> >> {
> >> struct page *page;
> >>
> >>- if (!(oldtce & (TCE_PCI_READ | TCE_PCI_WRITE)))
> >>- return;
> >>-
> >> /*
> >> * VFIO cannot map/unmap when a container is not enabled so
> >> * we would not need this check but KVM could map/unmap and if
> >>@@ -264,10 +261,6 @@ static void tce_iommu_unuse_page(struct tce_container *container,
> >> return;
> >>
> >> page = pfn_to_page(__pa(oldtce) >> PAGE_SHIFT);
> >>-
> >>- if (oldtce & TCE_PCI_WRITE)
> >>- SetPageDirty(page);
> >>-
> >
> >Seems to me that unuse_page() should get a direction parameter,
> >instead of moving the PageDirty (and DMA_NONE test) to all the
> >callers.
>
>
> Sorry, I am not following you here. There is just a single gateway for VFIO
> to the platform code which is iommu_tce_xchg() and this is where the
> SetPageDirty() check went. What are "all the callers"?

Oh, ok, I think I see. I just saw the dirty check being removed here,
and it's not obvious looking at this patch alone that iommu_tce_xchg()
is called at all the callsites of unuse_page.

--
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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Next message: David Gibson: "Re: [PATCH kernel v8 12/31] powerpc/spapr: vfio: Switch from iommu_table to new iommu_table_group"
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In reply to: Alexey Kardashevskiy: "Re: [PATCH kernel v8 17/31] powerpc/iommu/powernv: Release replaced TCE"
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