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

[Alexey Kardashevskiy <aik@ozlabs.ru>]

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 <aik@ozlabs.ru>
>> ---
>> 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