Re: [PATCH RFCv2 5/8] vfio/iommufd: Implement VFIOIOMMUClass::query_dirty_bitmap support

[Joao Martins <joao.m.martins@oracle.com>]

On 20/02/2024 12:52, Avihai Horon wrote:
> 
> On 20/02/2024 12:59, Joao Martins wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> On 19/02/2024 09:30, Avihai Horon wrote:
>>> Hi Joao,
>>>
>>> On 12/02/2024 15:56, Joao Martins wrote:
>>>> External email: Use caution opening links or attachments
>>>>
>>>>
>>>> ioctl(iommufd, IOMMU_HWPT_GET_DIRTY_BITMAP, arg) is the UAPI
>>>> that fetches the bitmap that tells what was dirty in an IOVA
>>>> range.
>>>>
>>>> A single bitmap is allocated and used across all the hwpts
>>>> sharing an IOAS which is then used in log_sync() to set Qemu
>>>> global bitmaps.
>>>>
>>>> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
>>>> ---
>>>>    backends/iommufd.c       | 24 ++++++++++++++++++++++++
>>>>    backends/trace-events    |  1 +
>>>>    hw/vfio/iommufd.c        | 30 ++++++++++++++++++++++++++++++
>>>>    include/sysemu/iommufd.h |  3 +++
>>>>    4 files changed, 58 insertions(+)
>>>>
>>>> diff --git a/backends/iommufd.c b/backends/iommufd.c
>>>> index 954de61c2da0..dd676d493c37 100644
>>>> --- a/backends/iommufd.c
>>>> +++ b/backends/iommufd.c
>>>> @@ -259,6 +259,30 @@ int iommufd_backend_set_dirty_tracking(IOMMUFDBackend
>>>> *be, uint32_t hwpt_id,
>>>>        return !ret ? 0 : -errno;
>>>>    }
>>>>
>>>> +int iommufd_backend_get_dirty_bitmap(IOMMUFDBackend *be, uint32_t hwpt_id,
>>>> +                                     uint64_t iova, ram_addr_t size,
>>>> +                                     uint64_t page_size, uint64_t *data)
>>>> +{
>>>> +    int ret;
>>>> +    struct iommu_hwpt_get_dirty_bitmap get_dirty_bitmap = {
>>>> +        .size = sizeof(get_dirty_bitmap),
>>>> +        .hwpt_id = hwpt_id,
>>>> +        .iova = iova, .length = size,
>>>> +        .page_size = page_size, .data = (uintptr_t)data,
>>> Member per line for readability?
>>>
>> Yeap
>>
>>>> +    };
>>>> +
>>>> +    ret = ioctl(be->fd, IOMMU_HWPT_GET_DIRTY_BITMAP, &get_dirty_bitmap);
>>>> +    trace_iommufd_backend_get_dirty_bitmap(be->fd, hwpt_id, iova, size,
>>>> +                                           page_size, ret);
>>>> +    if (ret) {
>>>> +        error_report("IOMMU_HWPT_GET_DIRTY_BITMAP (iova: 0x%"PRIx64
>>>> +                     " size: 0x%"PRIx64") failed: %s", iova,
>>>> +                     size, strerror(errno));
>>>> +    }
>>>> +
>>>> +    return !ret ? 0 : -errno;
>>>> +}
>>>> +
>>>>    static const TypeInfo iommufd_backend_info = {
>>>>        .name = TYPE_IOMMUFD_BACKEND,
>>>>        .parent = TYPE_OBJECT,
>>>> diff --git a/backends/trace-events b/backends/trace-events
>>>> index feba2baca5f7..11a27cb114b6 100644
>>>> --- a/backends/trace-events
>>>> +++ b/backends/trace-events
>>>> @@ -17,3 +17,4 @@ iommufd_backend_alloc_hwpt(int iommufd, uint32_t dev_id,
>>>> uint32_t pt_id, uint32_
>>>>    iommufd_backend_alloc_ioas(int iommufd, uint32_t ioas, int ret) " iommufd=%d
>>>> ioas=%d (%d)"
>>>>    iommufd_backend_free_id(int iommufd, uint32_t id, int ret) " iommufd=%d
>>>> id=%d (%d)"
>>>>    iommufd_backend_set_dirty(int iommufd, uint32_t hwpt_id, bool start, int
>>>> ret) " iommufd=%d hwpt=%d enable=%d (%d)"
>>>> +iommufd_backend_get_dirty_bitmap(int iommufd, uint32_t hwpt_id, uint64_t
>>>> iova, uint64_t size, uint64_t page_size, int ret) " iommufd=%d hwpt=%d
>>>> iova=0x%"PRIx64" size=0x%"PRIx64" page_size=0x%"PRIx64" (%d)"
>>> s/hwpt=%d/hwpt=%u
>>>
>> /me nods
>>
>>>> diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
>>>> index 361e659288fd..79b13bd262cc 100644
>>>> --- a/hw/vfio/iommufd.c
>>>> +++ b/hw/vfio/iommufd.c
>>>> @@ -25,6 +25,7 @@
>>>>    #include "qemu/cutils.h"
>>>>    #include "qemu/chardev_open.h"
>>>>    #include "pci.h"
>>>> +#include "exec/ram_addr.h"
>>>>    #include "migration/migration.h"
>>>>
>>>>    static int iommufd_cdev_map(const VFIOContainerBase *bcontainer, hwaddr
>>>> iova,
>>>> @@ -142,6 +143,34 @@ err:
>>>>        return ret;
>>>>    }
>>>>
>>>> +static int iommufd_query_dirty_bitmap(const VFIOContainerBase *bcontainer,
>>>> +                                      VFIOBitmap *vbmap, uint64_t iova,
>>>> +                                      uint64_t size)
>>>> +{
>>>> +    VFIOIOMMUFDContainer *container = container_of(bcontainer,
>>>> +                                                   VFIOIOMMUFDContainer,
>>>> +                                                   bcontainer);
>>>> +    int ret;
>>>> +    VFIOIOASHwpt *hwpt;
>>>> +    unsigned long page_size;
>>>> +
>>>> +    if (!bcontainer->dirty_pages_supported) {
>>> Do we need this check?
>>> IIUC, if we got to iommufd_query_dirty_bitmap(), it means
>>> bcontainer->dirty_pages_supported is already true.
>>>
>> Not quite. Look again at vfio_get_dirty_bitmap(); furthermore
>> vfio_container_query_dirty_bitmap() doesn't check for dirty_pages_supported.
> 
> vfio_get_dirty_bitmap() has this check at the beginning:
> 
> if (!bcontainer->dirty_pages_supported && !all_device_dirty_tracking) {
>     cpu_physical_memory_set_dirty_range(ram_addr, size,
>                                         tcg_enabled() ? DIRTY_CLIENTS_ALL :
>                                         DIRTY_CLIENTS_NOCODE);
>     return 0;
> }
> 
> So if bcontainer->dirty_pages_supported is false we will mark all dirty and
> return (and not call vfio_container_query_dirty_bitmap()).
> 
> Or am I missing something?
> 

Nah, I just lacked coffee.

You're right, while I read that check there, I misread what
vfio_devices_all_device_dirty_tracking() returns. And if that returns false it
means we need IOMMU dirty tracking and it was already tested false, otherwise
device dirty tracking is used instead.

	Joao