Re: [Qemu-devel] [PATCH qemu v10 13/14] vfio: spapr: Add SPAPR IOMMU v2 support (DMA memory preregistering)

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 07/07/2015 05:23 PM, Thomas Huth wrote:
> On Mon,  6 Jul 2015 12:11:09 +1000
> Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
>
>> This makes use of the new "memory registering" feature. The idea is
>> to provide the userspace ability to notify the host kernel about pages
>> which are going to be used for DMA. Having this information, the host
>> kernel can pin them all once per user process, do locked pages
>> accounting (once) and not spent time on doing that in real time with
>> possible failures which cannot be handled nicely in some cases.
>>
>> This adds a guest RAM memory listener which notifies a VFIO container
>> about memory which needs to be pinned/unpinned. VFIO MMIO regions
>> (i.e. "skip dump" regions) are skipped.
>>
>> The feature is only enabled for SPAPR IOMMU v2. The host kernel changes
>> are required. Since v2 does not need/support VFIO_IOMMU_ENABLE, this does
>> not call it when v2 is detected and enabled.
>>
>> This does not change the guest visible interface.
>>
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>> Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
>> ---
>> Changes:
>> v9:
>> * since there is no more SPAPR-specific data in container::iommu_data,
>> the memory preregistration fields are common and potentially can be used
>> by other architectures
>>
>> v7:
>> * in vfio_spapr_ram_listener_region_del(), do unref() after ioctl()
>> * s'ramlistener'register_listener'
>>
>> v6:
>> * fixed commit log (s/guest/userspace/), added note about no guest visible
>> change
>> * fixed error checking if ram registration failed
>> * added alignment check for section->offset_within_region
>>
>> v5:
>> * simplified the patch
>> * added trace points
>> * added round_up() for the size
>> * SPAPR IOMMU v2 used
>> ---
>>   hw/vfio/common.c              | 109 ++++++++++++++++++++++++++++++++++++++----
>>   include/hw/vfio/vfio-common.h |   3 ++
>>   trace-events                  |   1 +
>>   3 files changed, 104 insertions(+), 9 deletions(-)
>>
>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
>> index 8eacfd7..0c7ba8c 100644
>> --- a/hw/vfio/common.c
>> +++ b/hw/vfio/common.c
>> @@ -488,6 +488,76 @@ static void vfio_listener_release(VFIOContainer *container)
>>       memory_listener_unregister(&container->iommu_data.type1.listener);
>>   }
>>
>> +static void vfio_ram_do_region(VFIOContainer *container,
>> +                              MemoryRegionSection *section, unsigned long req)
>> +{
>> +    int ret;
>> +    struct vfio_iommu_spapr_register_memory reg = { .argsz = sizeof(reg) };
>> +
>> +    if (!memory_region_is_ram(section->mr) ||
>> +        memory_region_is_skip_dump(section->mr)) {
>> +        return;
>> +    }
>> +
>> +    if (unlikely((section->offset_within_region & (getpagesize() - 1)))) {
>> +        error_report("%s received unaligned region", __func__);
>> +        return;
>> +    }
>> +
>> +    reg.vaddr = (__u64) memory_region_get_ram_ptr(section->mr) +
>
> We're in usespace here ... I think it would be better to use uint64_t
> instead of the kernel-type __u64.


We are calling a kernel here - @reg is a kernel-defined struct.


>
>> +        section->offset_within_region;
>> +    reg.size = ROUND_UP(int128_get64(section->size), TARGET_PAGE_SIZE);
>> +
>> +    ret = ioctl(container->fd, req, &reg);
>> +    trace_vfio_ram_register(_IOC_NR(req) - VFIO_BASE, reg.vaddr, reg.size,
>> +            ret ? -errno : 0);
>> +    if (!ret) {
>> +        return;
>> +    }
>> +
>> +    /*
>> +     * On the initfn path, store the first error in the container so we
>> +     * can gracefully fail.  Runtime, there's not much we can do other
>> +     * than throw a hardware error.
>> +     */
>> +    if (!container->iommu_data.ram_reg_initialized) {
>> +        if (!container->iommu_data.ram_reg_error) {
>> +            container->iommu_data.ram_reg_error = -errno;
>> +        }
>> +    } else {
>> +        hw_error("vfio: RAM registering failed, unable to continue");
>> +    }
>> +}
>> +
>> +static void vfio_ram_listener_region_add(MemoryListener *listener,
>> +                                         MemoryRegionSection *section)
>> +{
>> +    VFIOContainer *container = container_of(listener, VFIOContainer,
>> +                                            iommu_data.register_listener);
>> +    memory_region_ref(section->mr);
>> +    vfio_ram_do_region(container, section, VFIO_IOMMU_SPAPR_REGISTER_MEMORY);
>> +}
>> +
>> +static void vfio_ram_listener_region_del(MemoryListener *listener,
>> +                                         MemoryRegionSection *section)
>> +{
>> +    VFIOContainer *container = container_of(listener, VFIOContainer,
>> +                                            iommu_data.register_listener);
>> +    vfio_ram_do_region(container, section, VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY);
>> +    memory_region_unref(section->mr);
>> +}
>> +
>> +static const MemoryListener vfio_ram_memory_listener = {
>> +    .region_add = vfio_ram_listener_region_add,
>> +    .region_del = vfio_ram_listener_region_del,
>> +};
>> +
>> +static void vfio_spapr_listener_release_v2(VFIOContainer *container)
>> +{
>> +    memory_listener_unregister(&container->iommu_data.register_listener);
>> +    vfio_listener_release(container);
>> +}
>> +
>>   int vfio_mmap_region(Object *obj, VFIORegion *region,
>>                        MemoryRegion *mem, MemoryRegion *submem,
>>                        void **map, size_t size, off_t offset,
>> @@ -698,14 +768,18 @@ static int vfio_connect_container(VFIOGroup *group, AddressSpace *as)
>>
>>           container->iommu_data.type1.initialized = true;
>>
>> -    } else if (ioctl(fd, VFIO_CHECK_EXTENSION, VFIO_SPAPR_TCE_IOMMU)) {
>> +    } else if (ioctl(fd, VFIO_CHECK_EXTENSION, VFIO_SPAPR_TCE_IOMMU) ||
>> +               ioctl(fd, VFIO_CHECK_EXTENSION, VFIO_SPAPR_TCE_v2_IOMMU)) {
>> +        bool v2 = !!ioctl(fd, VFIO_CHECK_EXTENSION, VFIO_SPAPR_TCE_v2_IOMMU);
>
> That "!!" sounds somewhat wrong here. I think you either want to check
> for "ioctl() == 1" (because only in this case you can be sure that v2
> is supported), or you can simply omit the "!!" because you're 100% sure
> that the ioctl only returns 0 or 1 (and never a negative error code).


The host kernel does not return an error on these ioctls, it returns 0 or 
1. And "!!" is shorter than "(bool)". VFIO_CHECK_EXTENSION for Type1 does 
exactly the same already.



>>           ret = ioctl(group->fd, VFIO_GROUP_SET_CONTAINER, &fd);
>>           if (ret) {
>>               error_report("vfio: failed to set group container: %m");
>>               ret = -errno;
>>               goto free_container_exit;
>>           }
>> -        ret = ioctl(fd, VFIO_SET_IOMMU, VFIO_SPAPR_TCE_IOMMU);
>> +        ret = ioctl(fd, VFIO_SET_IOMMU,
>> +                v2 ? VFIO_SPAPR_TCE_v2_IOMMU : VFIO_SPAPR_TCE_IOMMU);
>>           if (ret) {
>>               error_report("vfio: failed to set iommu for container: %m");
>>               ret = -errno;
>> @@ -717,19 +791,36 @@ static int vfio_connect_container(VFIOGroup *group, AddressSpace *as)
>>            * when container fd is closed so we do not call it explicitly
>>            * in this file.
>>            */
>> -        ret = ioctl(fd, VFIO_IOMMU_ENABLE);
>> -        if (ret) {
>> -            error_report("vfio: failed to enable container: %m");
>> -            ret = -errno;
>> -            goto free_container_exit;
>> +        if (!v2) {
>> +            ret = ioctl(fd, VFIO_IOMMU_ENABLE);
>> +            if (ret) {
>> +                error_report("vfio: failed to enable container: %m");
>> +                ret = -errno;
>> +                goto free_container_exit;
>> +            }
>>           }
>>
>>           container->iommu_data.type1.listener = vfio_memory_listener;
>> -        container->iommu_data.release = vfio_listener_release;
>> -
>>           memory_listener_register(&container->iommu_data.type1.listener,
>>                                    container->space->as);
>>
>> +        if (!v2) {
>> +            container->iommu_data.release = vfio_listener_release;
>> +        } else {
>> +            container->iommu_data.release = vfio_spapr_listener_release_v2;
>> +            container->iommu_data.register_listener =
>> +                    vfio_ram_memory_listener;
>> +            memory_listener_register(&container->iommu_data.register_listener,
>> +                                     &address_space_memory);
>> +
>> +            if (container->iommu_data.ram_reg_error) {
>> +                error_report("vfio: RAM memory listener initialization failed for container");
>
> Line > 80 columns?

afaik user visible strings are an exception in QEMU and kernel.


>
>> +                goto listener_release_exit;
>> +            }
>> +
>> +            container->iommu_data.ram_reg_initialized = true;
>> +        }
>> +
>
>   Thomas
>


-- 
Alexey