Re: [Qemu-devel] [PATCH qemu v14 17/18] vfio/spapr: Use VFIO_SPAPR_TCE_v2_IOMMU

[Alexey Kardashevskiy]

On 03/22/2016 04:14 PM, David Gibson wrote:
> On Mon, Mar 21, 2016 at 06:47:05PM +1100, Alexey Kardashevskiy wrote:
> > New VFIO_SPAPR_TCE_v2_IOMMU type supports dynamic DMA window management.
> > This adds ability to VFIO common code to dynamically allocate/remove
> > DMA windows in the host kernel when new VFIO container is added/removed.
> >
> > This adds VFIO_IOMMU_SPAPR_TCE_CREATE ioctl to vfio_listener_region_add
> > and adds just created IOMMU into the host IOMMU list; the opposite
> > action is taken in vfio_listener_region_del.
> >
> > When creating a new window, this uses euristic to decide on the TCE table
> > levels number.
> >
> > This should cause no guest visible change in behavior.
> >
> > Signed-off-by: Alexey Kardashevskiy <address@hidden>
> > ---
> > Changes:
> > v14:
> > * new to the series
> >
> > ---
> > TODO:
> > * export levels to PHB
> > ---
> >   hw/vfio/common.c | 108 ++++++++++++++++++++++++++++++++++++++++++++++++++++---
> >   trace-events     |   2 ++
> >   2 files changed, 105 insertions(+), 5 deletions(-)
> >
> > diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> > index 4e873b7..421d6eb 100644
> > --- a/hw/vfio/common.c
> > +++ b/hw/vfio/common.c
> > @@ -279,6 +279,14 @@ static int vfio_host_iommu_add(VFIOContainer *container,
> >       return 0;
> >   }
> >
> > +static void vfio_host_iommu_del(VFIOContainer *container, hwaddr min_iova)
> > +{
> > +    VFIOHostIOMMU *hiommu = vfio_host_iommu_lookup(container, min_iova, 
> > 0x1000);
>
> The hard-coded 0x1000 looks dubious..

Well, that's the minimal page size...


> > +    g_assert(hiommu);
> > +    QLIST_REMOVE(hiommu, hiommu_next);
> > +}
> > +
> >   static bool vfio_listener_skipped_section(MemoryRegionSection *section)
> >   {
> >       return (!memory_region_is_ram(section->mr) &&
> > @@ -392,6 +400,61 @@ static void vfio_listener_region_add(MemoryListener 
> > *listener,
> >       }
> >       end = int128_get64(llend);
> >
> > +    if (container->iommu_type == VFIO_SPAPR_TCE_v2_IOMMU) {
>
> I think this would be clearer split out into a helper function,
> vfio_create_host_window() or something.


It is rather vfio_spapr_create_host_window() and we were avoiding 
xxx_spapr_xxx so far. I'd cut-n-paste the SPAPR PCI AS listener to a 
separate file but this usually triggers more discussion and never ends well.



> > +        unsigned entries, pages;
> > +        struct vfio_iommu_spapr_tce_create create = { .argsz = sizeof(create) 
> > };
> > +
> > +        g_assert(section->mr->iommu_ops);
> > +        g_assert(memory_region_is_iommu(section->mr));
>
> I don't think you need these asserts.  AFAICT the same logic should
> work if a RAM MR was added directly to PCI address space - this would
> create the new host window, then the existing code for adding a RAM MR
> would map that block of RAM statically into the new window.

In what configuration/machine can we do that on SPAPR?


> > +        trace_vfio_listener_region_add_iommu(iova, end - 1);
> > +        /*
> > +         * FIXME: For VFIO iommu types which have KVM acceleration to
> > +         * avoid bouncing all map/unmaps through qemu this way, this
> > +         * would be the right place to wire that up (tell the KVM
> > +         * device emulation the VFIO iommu handles to use).
> > +         */
> > +        create.window_size = memory_region_size(section->mr);
> > +        create.page_shift =
> > +                ctz64(section->mr->iommu_ops->get_page_sizes(section->mr));
>
> Ah.. except that I guess you'd need to fall back to host page size
> here to handle a RAM MR.

Can you give an example of such RAM MR being added to PCI AS on SPAPR?


> > +        /*
> > +         * SPAPR host supports multilevel TCE tables, there is some
> > +         * euristic to decide how many levels we want for our table:
> > +         * 0..64 = 1; 65..4096 = 2; 4097..262144 = 3; 262145.. = 4
> > +         */
> > +        entries = create.window_size >> create.page_shift;
> > +        pages = (entries * sizeof(uint64_t)) / getpagesize();
> > +        create.levels = ctz64(pow2ceil(pages) - 1) / 6 + 1;
> > +
> > +        ret = ioctl(container->fd, VFIO_IOMMU_SPAPR_TCE_CREATE, &create);
> > +        if (ret) {
> > +            error_report("Failed to create a window, ret = %d (%m)", ret);
> > +            goto fail;
> > +        }
> > +
> > +        if (create.start_addr != section->offset_within_address_space ||
> > +            vfio_host_iommu_lookup(container, create.start_addr,
> > +                                   create.start_addr + create.window_size - 
> > 1)) {
>
> Under what circumstances can this trigger?  Is the kernel ioctl
> allowed to return a different window start address than the one
> requested?

You already asked this some time ago :) The userspace cannot request 
address, the host kernel returns one.


> The second check looks very strange - if it returns true doesn't that
> mean you *do* have host window which can accomodate this guest region,
> which is what you want?

This should not happen, this is what this check is for. Can make it 
assert() or something like this.


> > +            struct vfio_iommu_spapr_tce_remove remove = {
> > +                .argsz = sizeof(remove),
> > +                .start_addr = create.start_addr
> > +            };
> > +            error_report("Host doesn't support DMA window at %"HWADDR_PRIx", must 
> > be %"PRIx64,
> > +                         section->offset_within_address_space,
> > +                         create.start_addr);
> > +            ioctl(container->fd, VFIO_IOMMU_SPAPR_TCE_REMOVE, &remove);
> > +            ret = -EINVAL;
> > +            goto fail;
> > +        }
> > +        trace_vfio_spapr_create_window(create.page_shift,
> > +                                       create.window_size,
> > +                                       create.start_addr);
> > +
> > +        vfio_host_iommu_add(container, create.start_addr,
> > +                            create.start_addr + create.window_size - 1,
> > +                            1ULL << create.page_shift);
> > +    }
> > +
> >       if (!vfio_host_iommu_lookup(container, iova, end - 1)) {
> >           error_report("vfio: IOMMU container %p can't map guest IOVA region"
> >                        " 0x%"HWADDR_PRIx"..0x%"HWADDR_PRIx,
> > @@ -525,6 +588,22 @@ static void vfio_listener_region_del(MemoryListener 
> > *listener,
> >                        container, iova, end - iova, ret);
> >       }
> >
> > +    if (container->iommu_type == VFIO_SPAPR_TCE_v2_IOMMU) {
> > +        struct vfio_iommu_spapr_tce_remove remove = {
> > +            .argsz = sizeof(remove),
> > +            .start_addr = section->offset_within_address_space,
> > +        };
> > +        ret = ioctl(container->fd, VFIO_IOMMU_SPAPR_TCE_REMOVE, &remove);
> > +        if (ret) {
> > +            error_report("Failed to remove window at %"PRIx64,
> > +                         remove.start_addr);
> > +        }
> > +
> > +        vfio_host_iommu_del(container, section->offset_within_address_space);
> > +
> > +        trace_vfio_spapr_remove_window(remove.start_addr);
> > +    }
> > +
> >       if (iommu && iommu->iommu_ops && iommu->iommu_ops->vfio_stop) {
> >           iommu->iommu_ops->vfio_stop(section->mr);
> >       }
> > @@ -928,11 +1007,30 @@ static int vfio_connect_container(VFIOGroup *group, 
> > AddressSpace *as)
> >               goto listener_release_exit;
> >           }
> >
> > -        /* The default table uses 4K pages */
> > -        vfio_host_iommu_add(container, info.dma32_window_start,
> > -                            info.dma32_window_start +
> > -                            info.dma32_window_size - 1,
> > -                            0x1000);
> > +        if (v2) {
> > +            /*
> > +             * There is a default window in just created container.
> > +             * To make region_add/del simpler, we better remove this
> > +             * window now and let those iommu_listener callbacks
> > +             * create/remove them when needed.
> > +             */
> > +            struct vfio_iommu_spapr_tce_remove remove = {
> > +                .argsz = sizeof(remove),
> > +                .start_addr = info.dma32_window_start,
> > +            };
> > +            ret = ioctl(fd, VFIO_IOMMU_SPAPR_TCE_REMOVE, &remove);
> > +            if (ret) {
> > +                error_report("vfio: VFIO_IOMMU_SPAPR_TCE_REMOVE failed: %m");
> > +                ret = -errno;
> > +                goto free_container_exit;
> > +            }
> > +        } else {
> > +            /* The default table uses 4K pages */
> > +            vfio_host_iommu_add(container, info.dma32_window_start,
> > +                                info.dma32_window_start +
> > +                                info.dma32_window_size - 1,
> > +                                0x1000);
> > +        }
> >       } else {
> >           error_report("vfio: No available IOMMU models");
> >           ret = -EINVAL;
> > diff --git a/trace-events b/trace-events
> > index cc619e1..f2b75a3 100644
> > --- a/trace-events
> > +++ b/trace-events
> > @@ -1736,6 +1736,8 @@ vfio_region_finalize(const char *name, int index) "Device %s, 
> > region %d"
> >   vfio_region_mmaps_set_enabled(const char *name, bool enabled) "Region %s mmaps 
> > enabled: %d"
> >   vfio_ram_register(uint64_t va, uint64_t size, int ret) "va=%"PRIx64" 
> > size=%"PRIx64" ret=%d"
> >   vfio_ram_unregister(uint64_t va, uint64_t size, int ret) "va=%"PRIx64" 
> > size=%"PRIx64" ret=%d"
> > +vfio_spapr_create_window(int ps, uint64_t ws, uint64_t off) "pageshift=0x%x 
> > winsize=0x%"PRIx64" offset=0x%"PRIx64
> > +vfio_spapr_remove_window(uint64_t off) "offset=%"PRIx64
> >
> >   # hw/vfio/platform.c
> >   vfio_platform_base_device_init(char *name, int groupid) "%s belongs to group 
> > #%d"


--
Alexey