Re: [PATCH Kernel v20 4/8] vfio iommu: Add ioctl definition for dirty pages tracking

[Kirti Wankhede <kwankhede@nvidia.com>]

On 5/15/2020 4:29 PM, Cornelia Huck wrote:
> On Fri, 15 May 2020 02:07:43 +0530
> Kirti Wankhede <kwankhede@nvidia.com> wrote:
> 
>> IOMMU container maintains a list of all pages pinned by vfio_pin_pages API.
>> All pages pinned by vendor driver through this API should be considered as
>> dirty during migration. When container consists of IOMMU capable device and
>> all pages are pinned and mapped, then all pages are marked dirty.
>> Added support to start/stop dirtied pages tracking and to get bitmap of all
>> dirtied pages for requested IO virtual address range.
>>
>> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
>> Reviewed-by: Neo Jia <cjia@nvidia.com>
>> ---
>>   include/uapi/linux/vfio.h | 55 +++++++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 55 insertions(+)
>>
>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>> index ad9bb5af3463..123de3bc2dce 100644
>> --- a/include/uapi/linux/vfio.h
>> +++ b/include/uapi/linux/vfio.h
>> @@ -1033,6 +1033,12 @@ struct vfio_iommu_type1_dma_map {
>>   
>>   #define VFIO_IOMMU_MAP_DMA _IO(VFIO_TYPE, VFIO_BASE + 13)
>>   
>> +struct vfio_bitmap {
>> +	__u64        pgsize;	/* page size for bitmap in bytes */
>> +	__u64        size;	/* in bytes */
>> +	__u64 __user *data;	/* one bit per page */
>> +};
>> +
>>   /**
>>    * VFIO_IOMMU_UNMAP_DMA - _IOWR(VFIO_TYPE, VFIO_BASE + 14,
>>    *							struct vfio_dma_unmap)
>> @@ -1059,6 +1065,55 @@ struct vfio_iommu_type1_dma_unmap {
>>   #define VFIO_IOMMU_ENABLE	_IO(VFIO_TYPE, VFIO_BASE + 15)
>>   #define VFIO_IOMMU_DISABLE	_IO(VFIO_TYPE, VFIO_BASE + 16)
>>   
>> +/**
>> + * VFIO_IOMMU_DIRTY_PAGES - _IOWR(VFIO_TYPE, VFIO_BASE + 17,
>> + *                                     struct vfio_iommu_type1_dirty_bitmap)
>> + * IOCTL is used for dirty pages tracking.
>> + * Caller should set flag depending on which operation to perform, details as
>> + * below:
>> + *
>> + * When IOCTL is called with VFIO_IOMMU_DIRTY_PAGES_FLAG_START set, indicates
>> + * migration is active and IOMMU module should track pages which are dirtied or
>> + * potentially dirtied by device.
> 
> "Calling the IOCTL with VFIO_IOMMU_DIRTY_PAGES_FLAG_START instructs the
> IOMMU driver to track pages that are dirtied or potentially dirtied by
> the device; designed to be used when a migration is in progress."
> 
> ?
> 

Ok, updating.

>> + * Dirty pages are tracked until tracking is stopped by user application by
>> + * setting VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP flag.
> 
> "...by calling the IOCTL with VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP." ?
> 
>> + *
>> + * When IOCTL is called with VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP set, indicates
>> + * IOMMU should stop tracking dirtied pages.
> 
> "Calling the IOCTL with VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP instructs the
> IOMMU driver to stop tracking dirtied pages."
> 
> ?
> 

Ok.

>> + *
>> + * When IOCTL is called with VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP flag set,
>> + * IOCTL returns dirty pages bitmap for IOMMU container during migration for
>> + * given IOVA range.
> 
> "Calling the IOCTL with VFIO_IOMMU_DIRTY_PAGES_GET_BITMAP returns the
> dirty pages bitmap for the IOMMU container for a given IOVA range." ?
> 
> Q: How does this interact with the two other operations? I imagine
> getting an empty bitmap before _START 

No, if dirty page tracking is not started, get_bitmap IOCTL will fail 
with -EINVAL.

> and a bitmap-in-progress between
> _START and _STOP. > After _STOP, will subsequent calls always give the
> same bitmap?
>

No, return -EINVAL.


>> User must provide data[] as the structure
>> + * vfio_iommu_type1_dirty_bitmap_get through which user provides IOVA range and
>> + * pgsize.
> 
> "The user must specify the IOVA range and the pgsize through the
> vfio_iommu_type1_dirty_bitmap_get structure in the data[] portion."
> 
> ?
> 
>> This interface supports to get bitmap of smallest supported pgsize
>> + * only and can be modified in future to get bitmap of specified pgsize.
> 
> That's a current restriction? How can the user find out whether it has
> been lifted (or, more generally, find out which pgsize values are
> supported)?

Migration capability is added to IOMMU info chain. That gives supported 
pgsize bitmap by IOMMU driver.

> 
>> + * User must allocate memory for bitmap, zero the bitmap memory  and set size
>> + * of allocated memory in bitmap.size field.
> 
> "The user must provide a zeroed memory area for the bitmap memory and
> specify its size in bitmap.size."
> 
> ?
> 
>> One bit is used to represent one
>> + * page consecutively starting from iova offset. User should provide page size
>> + * in bitmap.pgsize field.
> 
> s/User/The user/
> 
> Is that the 'pgsize' the comment above talks about?
> 

By specifying pgsize here user can ask for bitmap of specific pgsize.

>> Bit set in bitmap indicates page at that offset from
>> + * iova is dirty.
> 
> "A bit set in the bitmap indicates that the page at that offset from
> iova is dirty." ?
> 
>> Caller must set argsz including size of structure
>> + * vfio_iommu_type1_dirty_bitmap_get.
> 
> s/Caller/The caller/
> 
> Does argz also include the size of the bitmap?

No.

> 
>> + *
>> + * Only one of the flags _START, STOP and _GET may be specified at a time.
> 
> s/STOP/_STOP/
> 
> (just to be consistent)
> 
>> + *
>> + */
>> +struct vfio_iommu_type1_dirty_bitmap {
>> +	__u32        argsz;
>> +	__u32        flags;
>> +#define VFIO_IOMMU_DIRTY_PAGES_FLAG_START	(1 << 0)
>> +#define VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP	(1 << 1)
>> +#define VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP	(1 << 2)
>> +	__u8         data[];
>> +};
>> +
>> +struct vfio_iommu_type1_dirty_bitmap_get {
>> +	__u64              iova;	/* IO virtual address */
>> +	__u64              size;	/* Size of iova range */
>> +	struct vfio_bitmap bitmap;
>> +};
> 
> That's for type1 only, right?
>

Yes.

Thanks,
Kirti

>> +
>> +#define VFIO_IOMMU_DIRTY_PAGES             _IO(VFIO_TYPE, VFIO_BASE + 17)
>> +
>>   /* -------- Additional API for SPAPR TCE (Server POWERPC) IOMMU -------- */
>>   
>>   /*
>