Re: [PATCH kernel v9 29/32] vfio: powerpc/spapr: Register memory and define IOMMU v2

David Gibson
2015-04-30T07:11:16Z

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On Sat, Apr 25, 2015 at 10:14:53PM +1000, Alexey Kardashevskiy wrote:
> The existing implementation accounts the whole DMA window in
> the locked_vm counter. This is going to be worse with multiple
> containers and huge DMA windows. Also, real-time accounting would requite
> additional tracking of accounted pages due to the page size difference -
> IOMMU uses 4K pages and system uses 4K or 64K pages.
>
> Another issue is that actual pages pinning/unpinning happens on every
> DMA map/unmap request. This does not affect the performance much now as
> we spend way too much time now on switching context between
> guest/userspace/host but this will start to matter when we add in-kernel
> DMA map/unmap acceleration.
>
> This introduces a new IOMMU type for SPAPR - VFIO_SPAPR_TCE_v2_IOMMU.
> New IOMMU deprecates VFIO_IOMMU_ENABLE/VFIO_IOMMU_DISABLE and introduces
> 2 new ioctls to register/unregister DMA memory -
> VFIO_IOMMU_SPAPR_REGISTER_MEMORY and VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY -
> which receive user space address and size of a memory region which
> needs to be pinned/unpinned and counted in locked_vm.
> New IOMMU splits physical pages pinning and TCE table update into 2 different
> operations. It requires 1) guest pages to be registered first 2) consequent
> map/unmap requests to work only with pre-registered memory.
> For the default single window case this means that the entire guest
> (instead of 2GB) needs to be pinned before using VFIO.
> When a huge DMA window is added, no additional pinning will be
> required, otherwise it would be guest RAM + 2GB.
>
> The new memory registration ioctls are not supported by
> VFIO_SPAPR_TCE_IOMMU. Dynamic DMA window and in-kernel acceleration
> will require memory to be preregistered in order to work.
>
> The accounting is done per the user process.
>
> This advertises v2 SPAPR TCE IOMMU and restricts what the userspace
> can do with v1 or v2 IOMMUs.
>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> [aw: for the vfio related changes]
> Acked-by: Alex Williamson <alex.williamson@redhat.com>
> ---
> Changes:
> v9:
> * s/tce_get_hva_cached/tce_iommu_use_page_v2/
>
> v7:
> * now memory is registered per mm (i.e. process)
> * moved memory registration code to powerpc/mmu
> * merged "vfio: powerpc/spapr: Define v2 IOMMU" into this
> * limited new ioctls to v2 IOMMU
> * updated doc
> * unsupported ioclts return -ENOTTY instead of -EPERM
>
> v6:
> * tce_get_hva_cached() returns hva via a pointer
>
> v4:
> * updated docs
> * s/kzmalloc/vzalloc/
> * in tce_pin_pages()/tce_unpin_pages() removed @vaddr, @size and
> replaced offset with index
> * renamed vfio_iommu_type_register_memory to vfio_iommu_spapr_register_memory
> and removed duplicating vfio_iommu_spapr_register_memory
> ---
> Documentation/vfio.txt | 23 ++++
> drivers/vfio/vfio_iommu_spapr_tce.c | 230 +++++++++++++++++++++++++++++++++++-
> include/uapi/linux/vfio.h | 27 +++++
> 3 files changed, 274 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/vfio.txt b/Documentation/vfio.txt
> index 96978ec..94328c8 100644
> --- a/Documentation/vfio.txt
> +++ b/Documentation/vfio.txt
> @@ -427,6 +427,29 @@ The code flow from the example above should be slightly changed:
>
> ....
>
> +5) There is v2 of SPAPR TCE IOMMU. It deprecates VFIO_IOMMU_ENABLE/
> +VFIO_IOMMU_DISABLE and implements 2 new ioctls:
> +VFIO_IOMMU_SPAPR_REGISTER_MEMORY and VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY
> +(which are unsupported in v1 IOMMU).

A summary of the semantic differeces between v1 and v2 would be nice.
At this point it's not really clear to me if there's a case for
creating v2, or if this could just be done by adding (optional)
functionality to v1.

> +PPC64 paravirtualized guests generate a lot of map/unmap requests,
> +and the handling of those includes pinning/unpinning pages and updating
> +mm::locked_vm counter to make sure we do not exceed the rlimit.
> +The v2 IOMMU splits accounting and pinning into separate operations:
> +
> +- VFIO_IOMMU_SPAPR_REGISTER_MEMORY/VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY ioctls
> +receive a user space address and size of the block to be pinned.
> +Bisecting is not supported and VFIO_IOMMU_UNREGISTER_MEMORY is expected to
> +be called with the exact address and size used for registering
> +the memory block. The userspace is not expected to call these often.
> +The ranges are stored in a linked list in a VFIO container.
> +
> +- VFIO_IOMMU_MAP_DMA/VFIO_IOMMU_UNMAP_DMA ioctls only update the actual
> +IOMMU table and do not do pinning; instead these check that the userspace
> +address is from pre-registered range.
> +
> +This separation helps in optimizing DMA for guests.
> +
> -------------------------------------------------------------------------------
>
> [1] VFIO was originally an acronym for "Virtual Function I/O" in its
> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> index 892a584..4cfc2c1 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c

So, from things you said at other points, I thought the idea was that
this registration stuff could also be used on non-Power IOMMUs. Did I
misunderstand, or is that a possibility for the future?

> @@ -21,6 +21,7 @@
> #include <linux/vfio.h>
> #include <asm/iommu.h>
> #include <asm/tce.h>
> +#include <asm/mmu_context.h>
>
> #define DRIVER_VERSION "0.1"
> #define DRIVER_AUTHOR "aik@ozlabs.ru"
> @@ -91,8 +92,58 @@ struct tce_container {
> struct iommu_group *grp;
> bool enabled;
> unsigned long locked_pages;
> + bool v2;
> };
>
> +static long tce_unregister_pages(struct tce_container *container,
> + __u64 vaddr, __u64 size)
> +{
> + long ret;
> + struct mm_iommu_table_group_mem_t *mem;
> +
> + if ((vaddr & ~PAGE_MASK) || (size & ~PAGE_MASK))
> + return -EINVAL;
> +
> + mem = mm_iommu_get(vaddr, size >> PAGE_SHIFT);
> + if (!mem)
> + return -EINVAL;
> +
> + ret = mm_iommu_put(mem); /* undo kref_get() from mm_iommu_get() */
> + if (!ret)
> + ret = mm_iommu_put(mem);
> +
> + return ret;
> +}
> +
> +static long tce_register_pages(struct tce_container *container,
> + __u64 vaddr, __u64 size)
> +{
> + long ret = 0;
> + struct mm_iommu_table_group_mem_t *mem;
> + unsigned long entries = size >> PAGE_SHIFT;
> +
> + if ((vaddr & ~PAGE_MASK) || (size & ~PAGE_MASK) ||
> + ((vaddr + size) < vaddr))
> + return -EINVAL;
> +
> + mem = mm_iommu_get(vaddr, entries);
> + if (!mem) {
> + ret = try_increment_locked_vm(entries);
> + if (ret)
> + return ret;
> +
> + ret = mm_iommu_alloc(vaddr, entries, &mem);
> + if (ret) {
> + decrement_locked_vm(entries);
> + return ret;
> + }
> + }
> +
> + container->enabled = true;
> +
> + return 0;
> +}

So requiring that registered regions get unregistered with exactly the
same addr/length is reasonable. I'm a bit less convinced that
disallowing overlaps is a good idea. What if two libraries in the
same process are trying to use VFIO - they may not know if the regions
they try to register are overlapping.

> static bool tce_page_is_contained(struct page *page, unsigned page_shift)
> {
> /*
> @@ -205,7 +256,7 @@ static void *tce_iommu_open(unsigned long arg)
> {
> struct tce_container *container;
>
> - if (arg != VFIO_SPAPR_TCE_IOMMU) {
> + if ((arg != VFIO_SPAPR_TCE_IOMMU) && (arg != VFIO_SPAPR_TCE_v2_IOMMU)) {
> pr_err("tce_vfio: Wrong IOMMU type\n");
> return ERR_PTR(-EINVAL);
> }
> @@ -215,6 +266,7 @@ static void *tce_iommu_open(unsigned long arg)
> return ERR_PTR(-ENOMEM);
>
> mutex_init(&container->lock);
> + container->v2 = arg == VFIO_SPAPR_TCE_v2_IOMMU;
>
> return container;
> }
> @@ -243,6 +295,47 @@ static void tce_iommu_unuse_page(struct tce_container *container,
> put_page(page);
> }
>
> +static int tce_iommu_use_page_v2(unsigned long tce, unsigned long size,
> + unsigned long *phpa, struct mm_iommu_table_group_mem_t **pmem)
> +{
> + long ret = 0;
> + struct mm_iommu_table_group_mem_t *mem;
> +
> + mem = mm_iommu_lookup(tce, size);
> + if (!mem)
> + return -EINVAL;
> +
> + ret = mm_iommu_ua_to_hpa(mem, tce, phpa);
> + if (ret)
> + return -EINVAL;
> +
> + *pmem = mem;
> +
> + return 0;
> +}
> +
> +static void tce_iommu_unuse_page_v2(struct iommu_table *tbl,
> + unsigned long entry)
> +{
> + struct mm_iommu_table_group_mem_t *mem = NULL;
> + int ret;
> + unsigned long hpa = 0;
> + unsigned long *pua = IOMMU_TABLE_USERSPACE_ENTRY(tbl, entry);
> +
> + if (!pua || !current || !current->mm)
> + return;
> +
> + ret = tce_iommu_use_page_v2(*pua, IOMMU_PAGE_SIZE(tbl),
> + &hpa, &mem);
> + if (ret)
> + pr_debug("%s: tce %lx at #%lx was not cached, ret=%d\n",
> + __func__, *pua, entry, ret);
> + if (mem)
> + mm_iommu_mapped_update(mem, false);
> +
> + *pua = 0;
> +}
> +
> static int tce_iommu_clear(struct tce_container *container,
> struct iommu_table *tbl,
> unsigned long entry, unsigned long pages)
> @@ -261,6 +354,11 @@ static int tce_iommu_clear(struct tce_container *container,
> if (direction == DMA_NONE)
> continue;
>
> + if (container->v2) {
> + tce_iommu_unuse_page_v2(tbl, entry);
> + continue;
> + }
> +
> tce_iommu_unuse_page(container, oldtce);
> }
>
> @@ -327,6 +425,62 @@ static long tce_iommu_build(struct tce_container *container,
> return ret;
> }
>
> +static long tce_iommu_build_v2(struct tce_container *container,
> + struct iommu_table *tbl,
> + unsigned long entry, unsigned long tce, unsigned long pages,
> + enum dma_data_direction direction)
> +{
> + long i, ret = 0;
> + struct page *page;
> + unsigned long hpa;
> + enum dma_data_direction dirtmp;
> +
> + for (i = 0; i < pages; ++i) {
> + struct mm_iommu_table_group_mem_t *mem = NULL;
> + unsigned long *pua = IOMMU_TABLE_USERSPACE_ENTRY(tbl,
> + entry + i);
> +
> + ret = tce_iommu_use_page_v2(tce, IOMMU_PAGE_SIZE(tbl),
> + &hpa, &mem);
> + if (ret)
> + break;
> +
> + page = pfn_to_page(hpa >> PAGE_SHIFT);
> + if (!tce_page_is_contained(page, tbl->it_page_shift)) {
> + ret = -EPERM;
> + break;
> + }
> +
> + /* Preserve offset within IOMMU page */
> + hpa |= tce & IOMMU_PAGE_MASK(tbl) & ~PAGE_MASK;
> + dirtmp = direction;
> +
> + ret = iommu_tce_xchg(tbl, entry + i, &hpa, &dirtmp);
> + if (ret) {
> + /* dirtmp cannot be DMA_NONE here */
> + tce_iommu_unuse_page_v2(tbl, entry + i);
> + pr_err("iommu_tce: %s failed ioba=%lx, tce=%lx, ret=%ld\n",
> + __func__, entry << tbl->it_page_shift,
> + tce, ret);
> + break;
> + }
> +
> + mm_iommu_mapped_update(mem, true);
> +
> + if (dirtmp != DMA_NONE)
> + tce_iommu_unuse_page_v2(tbl, entry + i);
> +
> + *pua = tce;
> +
> + tce += IOMMU_PAGE_SIZE(tbl);
> + }
> +
> + if (ret)
> + tce_iommu_clear(container, tbl, entry, i);
> +
> + return ret;
> +}
> +
> static long tce_iommu_ioctl(void *iommu_data,
> unsigned int cmd, unsigned long arg)
> {
> @@ -338,6 +492,7 @@ static long tce_iommu_ioctl(void *iommu_data,
> case VFIO_CHECK_EXTENSION:
> switch (arg) {
> case VFIO_SPAPR_TCE_IOMMU:
> + case VFIO_SPAPR_TCE_v2_IOMMU:
> ret = 1;
> break;
> default:
> @@ -425,11 +580,18 @@ static long tce_iommu_ioctl(void *iommu_data,
> if (ret)
> return ret;
>
> - ret = tce_iommu_build(container, tbl,
> - param.iova >> tbl->it_page_shift,
> - param.vaddr,
> - param.size >> tbl->it_page_shift,
> - direction);
> + if (container->v2)
> + ret = tce_iommu_build_v2(container, tbl,
> + param.iova >> tbl->it_page_shift,
> + param.vaddr,
> + param.size >> tbl->it_page_shift,
> + direction);
> + else
> + ret = tce_iommu_build(container, tbl,
> + param.iova >> tbl->it_page_shift,
> + param.vaddr,
> + param.size >> tbl->it_page_shift,
> + direction);
>
> iommu_flush_tce(tbl);
>
> @@ -474,7 +636,60 @@ static long tce_iommu_ioctl(void *iommu_data,
>
> return ret;
> }
> + case VFIO_IOMMU_SPAPR_REGISTER_MEMORY: {
> + struct vfio_iommu_spapr_register_memory param;
> +
> + if (!container->v2)
> + break;
> +
> + minsz = offsetofend(struct vfio_iommu_spapr_register_memory,
> + size);
> +
> + if (copy_from_user(&param, (void __user *)arg, minsz))
> + return -EFAULT;
> +
> + if (param.argsz < minsz)
> + return -EINVAL;
> +
> + /* No flag is supported now */
> + if (param.flags)
> + return -EINVAL;
> +
> + mutex_lock(&container->lock);
> + ret = tce_register_pages(container, param.vaddr, param.size);
> + mutex_unlock(&container->lock);

AFAICT, this is the only call to tce_register_pages(), so why not put
the mutex into the function.

> +
> + return ret;
> + }
> + case VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY: {
> + struct vfio_iommu_spapr_register_memory param;
> +
> + if (!container->v2)
> + break;
> +
> + minsz = offsetofend(struct vfio_iommu_spapr_register_memory,
> + size);
> +
> + if (copy_from_user(&param, (void __user *)arg, minsz))
> + return -EFAULT;
> +
> + if (param.argsz < minsz)
> + return -EINVAL;
> +
> + /* No flag is supported now */
> + if (param.flags)
> + return -EINVAL;
> +
> + mutex_lock(&container->lock);
> + tce_unregister_pages(container, param.vaddr, param.size);
> + mutex_unlock(&container->lock);
> +
> + return 0;
> + }
> case VFIO_IOMMU_ENABLE:
> + if (container->v2)
> + break;
> +
> mutex_lock(&container->lock);
> ret = tce_iommu_enable(container);
> mutex_unlock(&container->lock);
> @@ -482,6 +697,9 @@ static long tce_iommu_ioctl(void *iommu_data,
>
>
> case VFIO_IOMMU_DISABLE:
> + if (container->v2)
> + break;
> +
> mutex_lock(&container->lock);
> tce_iommu_disable(container);
> mutex_unlock(&container->lock);
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index b57b750..8fdcfb9 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -36,6 +36,8 @@
> /* Two-stage IOMMU */
> #define VFIO_TYPE1_NESTING_IOMMU 6 /* Implies v2 */
>
> +#define VFIO_SPAPR_TCE_v2_IOMMU 7
> +
> /*
> * The IOCTL interface is designed for extensibility by embedding the
> * structure length (argsz) and flags into structures passed between
> @@ -495,6 +497,31 @@ struct vfio_eeh_pe_op {
>
> #define VFIO_EEH_PE_OP _IO(VFIO_TYPE, VFIO_BASE + 21)
>
> +/**
> + * VFIO_IOMMU_SPAPR_REGISTER_MEMORY - _IOW(VFIO_TYPE, VFIO_BASE + 17, struct vfio_iommu_spapr_register_memory)
> + *
> + * Registers user space memory where DMA is allowed. It pins
> + * user pages and does the locked memory accounting so
> + * subsequent VFIO_IOMMU_MAP_DMA/VFIO_IOMMU_UNMAP_DMA calls
> + * get faster.
> + */
> +struct vfio_iommu_spapr_register_memory {
> + __u32 argsz;
> + __u32 flags;
> + __u64 vaddr; /* Process virtual address */
> + __u64 size; /* Size of mapping (bytes) */
> +};
> +#define VFIO_IOMMU_SPAPR_REGISTER_MEMORY _IO(VFIO_TYPE, VFIO_BASE + 17)
> +
> +/**
> + * VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY - _IOW(VFIO_TYPE, VFIO_BASE + 18, struct vfio_iommu_spapr_register_memory)
> + *
> + * Unregisters user space memory registered with
> + * VFIO_IOMMU_SPAPR_REGISTER_MEMORY.
> + * Uses vfio_iommu_spapr_register_memory for parameters.
> + */
> +#define VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY _IO(VFIO_TYPE, VFIO_BASE + 18)
> +
> /* ***************************************************************** */
>
> #endif /* _UAPIVFIO_H */

--
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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