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Mon, 10 Feb 2020 17:25:18 +0000 (UTC) Received: from x1.home (ovpn-116-28.phx2.redhat.com [10.3.116.28]) by smtp.corp.redhat.com (Postfix) with ESMTP id D340E8ED05; Mon, 10 Feb 2020 17:25:15 +0000 (UTC) Date: Mon, 10 Feb 2020 10:25:15 -0700 From: Alex Williamson To: Kirti Wankhede Subject: Re: [PATCH v12 Kernel 1/7] vfio: KABI for migration interface for device state Message-ID: <20200210102515.0c85cc0a@x1.home> In-Reply-To: <1581104554-10704-2-git-send-email-kwankhede@nvidia.com> References: <1581104554-10704-1-git-send-email-kwankhede@nvidia.com> <1581104554-10704-2-git-send-email-kwankhede@nvidia.com> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Zhengxiao.zx@Alibaba-inc.com, kevin.tian@intel.com, yi.l.liu@intel.com, cjia@nvidia.com, kvm@vger.kernel.org, eskultet@redhat.com, ziye.yang@intel.com, qemu-devel@nongnu.org, cohuck@redhat.com, shuangtai.tst@alibaba-inc.com, dgilbert@redhat.com, zhi.a.wang@intel.com, mlevitsk@redhat.com, pasic@linux.ibm.com, aik@ozlabs.ru, eauger@redhat.com, felipe@nutanix.com, jonathan.davies@nutanix.com, yan.y.zhao@intel.com, changpeng.liu@intel.com, Ken.Xue@amd.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Sat, 8 Feb 2020 01:12:28 +0530 Kirti Wankhede wrote: > - Defined MIGRATION region type and sub-type. > > - Defined vfio_device_migration_info structure which will be placed at 0th > offset of migration region to get/set VFIO device related information. > Defined members of structure and usage on read/write access. > > - Defined device states and state transition details. > > - Defined sequence to be followed while saving and resuming VFIO device. > > Signed-off-by: Kirti Wankhede > Reviewed-by: Neo Jia > --- > include/uapi/linux/vfio.h | 208 ++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 208 insertions(+) > > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h > index 9e843a147ead..572242620ce9 100644 > --- a/include/uapi/linux/vfio.h > +++ b/include/uapi/linux/vfio.h > @@ -305,6 +305,7 @@ struct vfio_region_info_cap_type { > #define VFIO_REGION_TYPE_PCI_VENDOR_MASK (0xffff) > #define VFIO_REGION_TYPE_GFX (1) > #define VFIO_REGION_TYPE_CCW (2) > +#define VFIO_REGION_TYPE_MIGRATION (3) > > /* sub-types for VFIO_REGION_TYPE_PCI_* */ > > @@ -379,6 +380,213 @@ struct vfio_region_gfx_edid { > /* sub-types for VFIO_REGION_TYPE_CCW */ > #define VFIO_REGION_SUBTYPE_CCW_ASYNC_CMD (1) > > +/* sub-types for VFIO_REGION_TYPE_MIGRATION */ > +#define VFIO_REGION_SUBTYPE_MIGRATION (1) > + > +/* > + * Structure vfio_device_migration_info is placed at 0th offset of > + * VFIO_REGION_SUBTYPE_MIGRATION region to get/set VFIO device related migration > + * information. Field accesses from this structure are only supported at their > + * native width and alignment, otherwise the result is undefined and vendor > + * drivers should return an error. > + * > + * device_state: (read/write) > + * - User application writes this field to inform vendor driver about the > + * device state to be transitioned to. > + * - Vendor driver should take necessary actions to change device state. > + * On successful transition to given state, vendor driver should return > + * success on write(device_state, state) system call. If device state > + * transition fails, vendor driver should return error, -EFAULT. s/error, -EFAULT/an appropriate -errno for the fault condition/ > + * - On user application side, if device state transition fails, i.e. if > + * write(device_state, state) returns error, read device_state again to > + * determine the current state of the device from vendor driver. > + * - Vendor driver should return previous state of the device unless vendor > + * driver has encountered an internal error, in which case vendor driver > + * may report the device_state VFIO_DEVICE_STATE_ERROR. > + * - User application must use the device reset ioctl in order to recover > + * the device from VFIO_DEVICE_STATE_ERROR state. If the device is > + * indicated in a valid device state via reading device_state, the user > + * application may decide attempt to transition the device to any valid > + * state reachable from the current state or terminate itself. > + * > + * device_state consists of 3 bits: > + * - If bit 0 set, indicates _RUNNING state. When it's clear, that > + * indicates _STOP state. When device is changed to _STOP, driver should > + * stop device before write() returns. > + * - If bit 1 set, indicates _SAVING state. When set, that indicates driver > + * should start gathering device state information which will be provided > + * to VFIO user application to save device's state. > + * - If bit 2 set, indicates _RESUMING state. When set, that indicates > + * prepare to resume device, data provided through migration region > + * should be used to resume device. > + * Bits 3 - 31 are reserved for future use. In order to preserve them, > + * user application should perform read-modify-write operation on this > + * field when modifying the specified bits. > + * > + * +------- _RESUMING > + * |+------ _SAVING > + * ||+----- _RUNNING > + * ||| > + * 000b => Device Stopped, not saving or resuming > + * 001b => Device running state, default state > + * 010b => Stop Device & save device state, stop-and-copy state > + * 011b => Device running and save device state, pre-copy state > + * 100b => Device stopped and device state is resuming > + * 101b => Invalid state > + * 110b => Error state > + * 111b => Invalid state > + * > + * State transitions: > + * > + * _RESUMING _RUNNING Pre-copy Stop-and-copy _STOP > + * (100b) (001b) (011b) (010b) (000b) > + * 0. Running or Default state > + * | > + * > + * 1. Normal Shutdown (optional) > + * |------------------------------------->| > + * > + * 2. Save state or Suspend > + * |------------------------->|---------->| > + * > + * 3. Save state during live migration > + * |----------->|------------>|---------->| > + * > + * 4. Resuming > + * |<---------| > + * > + * 5. Resumed > + * |--------->| > + * > + * 0. Default state of VFIO device is _RUNNNG when user application starts. > + * 1. During normal user application shutdown, vfio device state changes > + * from _RUNNING to _STOP. This is optional, user application may or may not > + * perform this state transition and vendor driver may not need. s/may not need/must not require, but must support this transition/ > + * 2. When user application save state or suspend application, device state > + * transitions from _RUNNING to stop-and-copy state and then to _STOP. > + * On state transition from _RUNNING to stop-and-copy, driver must > + * stop device, save device state and send it to application through > + * migration region. Sequence to be followed for such transition is given > + * below. > + * 3. In user application live migration, state transitions from _RUNNING > + * to pre-copy to stop-and-copy to _STOP. > + * On state transition from _RUNNING to pre-copy, driver should start > + * gathering device state while application is still running and send device > + * state data to application through migration region. > + * On state transition from pre-copy to stop-and-copy, driver must stop > + * device, save device state and send it to user application through > + * migration region. > + * Sequence to be followed for above two transitions is given below. Perhaps adding something like "Vendor drivers must support the pre-copy state even for implementations where no data is provided to the user until the stop-and-copy state. The user must not be required to consume all migration data prior to transitioning to a new state, including the stop-and-copy state." > + * 4. To start resuming phase, device state should be transitioned from > + * _RUNNING to _RESUMING state. > + * In _RESUMING state, driver should use received device state data through > + * migration region to resume device. > + * 5. On providing saved device data to driver, application should change state > + * from _RESUMING to _RUNNING. > + * > + * pending bytes: (read only) > + * Number of pending bytes yet to be migrated from vendor driver > + * > + * data_offset: (read only) > + * User application should read data_offset in migration region from where > + * user application should read device data during _SAVING state or write > + * device data during _RESUMING state. See below for detail of sequence to > + * be followed. > + * > + * data_size: (read/write) > + * User application should read data_size to get size of data copied in > + * bytes in migration region during _SAVING state and write size of data > + * copied in bytes in migration region during _RESUMING state. > + * > + * Migration region looks like: > + * ------------------------------------------------------------------ > + * |vfio_device_migration_info| data section | > + * | | /////////////////////////////// | > + * ------------------------------------------------------------------ > + * ^ ^ > + * offset 0-trapped part data_offset > + * > + * Structure vfio_device_migration_info is always followed by data section in > + * the region, so data_offset will always be non-0. Offset from where data is > + * copied is decided by kernel driver, data section can be trapped or mapped > + * or partitioned, depending on how kernel driver defines data section. > + * Data section partition can be defined as mapped by sparse mmap capability. > + * If mmapped, then data_offset should be page aligned, where as initial section > + * which contain vfio_device_migration_info structure might not end at offset > + * which is page aligned. The user is not required to access via mmap regardless > + * of the region mmap capabilities. > + * Vendor driver should decide whether to partition data section and how to > + * partition the data section. Vendor driver should return data_offset > + * accordingly. > + * > + * Sequence to be followed for _SAVING|_RUNNING device state or pre-copy phase > + * and for _SAVING device state or stop-and-copy phase: > + * a. read pending_bytes, indicates start of new iteration to get device data. > + * Repeatative read on pending_bytes at this stage should have no side > + * effect. s/Repeatative/Repeated/ > + * If pending_bytes == 0, user application should not iterate to get data > + * for that device. > + * If pending_bytes > 0, go through below steps. > + * b. read data_offset, indicates vendor driver to make data available through > + * data section. Vendor driver should return this read operation only after > + * data is available from (region + data_offset) to (region + data_offset + > + * data_size). > + * c. read data_size, amount of data in bytes available through migration > + * region. > + * Read on data_offset and data_size should return offset and size of current > + * buffer if user application reads those more than once here. > + * d. read data of data_size bytes from (region + data_offset) from migration > + * region. > + * e. process data. > + * f. read pending_bytes, this read operation indicates data from previous > + * iteration had read. If pending_bytes > 0, goto step b. > + * > + * If there is any error during the above sequence, vendor driver can return > + * error code for next read()/write() operation, that will terminate the loop > + * and user should take next necessary action, for example, fail migration or > + * terminate user application. > + * > + * User application can transition from _SAVING|_RUNNING (pre-copy state) to > + * _SAVING (stop-and-copy) state regardless of pending bytes. Ok, you cover one of my concerns above here. Maybe doesn't hurt to mention in both places. > + * User application should iterate in _SAVING (stop-and-copy) until > + * pending_bytes is 0. > + * > + * Sequence to be followed while _RESUMING device state: > + * While data for this device is available, repeat below steps: > + * a. read data_offset from where user application should write data. > + * b. write data of data_size to migration region from data_offset. Data size > + * should be data packet size at source during _SAVING. I find the reference to data_size a bit confusing in this wording, almost as if it's implied that the user reads data_size on the target. What if we changed it a little: b. write migration data starting at migration region + data_offset for length determined by data_size from the migration source. > + * c. write data_size which indicates vendor driver that data is written in > + * migration region. Vendor driver should read this data from migration > + * region and resume device's state. Perhaps "Vendor driver should apply the user provided migration region data towards the device resume state"? > + * > + * For user application, data is opaque. User application should write data in > + * the same order as received and should of same transaction size at source. Great! > + */ > + > +struct vfio_device_migration_info { > + __u32 device_state; /* VFIO device state */ > +#define VFIO_DEVICE_STATE_STOP (0) > +#define VFIO_DEVICE_STATE_RUNNING (1 << 0) > +#define VFIO_DEVICE_STATE_SAVING (1 << 1) > +#define VFIO_DEVICE_STATE_RESUMING (1 << 2) > +#define VFIO_DEVICE_STATE_MASK (VFIO_DEVICE_STATE_RUNNING | \ > + VFIO_DEVICE_STATE_SAVING | \ > + VFIO_DEVICE_STATE_RESUMING) > + > +#define VFIO_DEVICE_STATE_VALID(state) \ > + (state & VFIO_DEVICE_STATE_RESUMING ? \ > + (state & VFIO_DEVICE_STATE_MASK) == VFIO_DEVICE_STATE_RESUMING : 1) > + > +#define VFIO_DEVICE_STATE_ERROR \ > + (VFIO_DEVICE_STATE_SAVING | VFIO_DEVICE_STATE_RESUMING) It looks like this isn't used in this series, so I'm not sure the intention of this macro, but I think we decided to only use 110b as the "error" state. So should this be something like #define VFIO_DEVICE_STATE_IS_ERROR(state) \ (state & VFIO_DEVICE_STATE_MASK == (VFIO_DEVICE_STATE_SAVING | \ VFIO_DEVICE_STATE_RESUMING)) Or if this was intended to be used in setting the device_state to error, perhaps #define VFIO_DEVICE_STATE_SET_ERROR(state) \ ((state & ~VFIO_DEVICE_STATE_MASK) | VFIO_DEVICE_SATE_SAVING | \ VFIO_DEVICE_STATE_RESUMING) > + > + __u32 reserved; Can we specify this reserved field as reads return zero, writes are ignored so that we give ourselves the opportunity to re-purpose it later? > + __u64 pending_bytes; > + __u64 data_offset; > + __u64 data_size; > +} __attribute__((packed)); > + > /* > * The MSIX mappable capability informs that MSIX data of a BAR can be mmapped > * which allows direct access to non-MSIX registers which happened to be within Thanks, Alex