mirror of https://gitee.com/openkylin/linux.git
vfio-ccw: update documentation
The vfio-ccw documentation comes from the cover letter of the original patch submission, which shows in some parts. Give it some love; in particular: - Remove/rework statements that make sense in a cover letter, but not in regular documentation. - Fix some typos. - Describe the current limitations in more detail. Acked-by: Halil Pasic <pasic@linux.vnet.ibm.com> Reviewed-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
This commit is contained in:
Cornelia Huck
parent
5628683cf7
commit
69cfd92ea4
|
|
@ -28,7 +28,7 @@ every detail. More information/reference could be found here:
|
|||
https://en.wikipedia.org/wiki/Channel_I/O
|
||||
- s390 architecture:
|
||||
s390 Principles of Operation manual (IBM Form. No. SA22-7832)
|
||||
- The existing Qemu code which implements a simple emulated channel
|
||||
- The existing QEMU code which implements a simple emulated channel
|
||||
subsystem could also be a good reference. It makes it easier to follow
|
||||
the flow.
|
||||
qemu/hw/s390x/css.c
|
||||
|
|
@ -39,22 +39,22 @@ For vfio mediated device framework:
|
|||
Motivation of vfio-ccw
|
||||
----------------------
|
||||
|
||||
Currently, a guest virtualized via qemu/kvm on s390 only sees
|
||||
Typically, a guest virtualized via QEMU/KVM on s390 only sees
|
||||
paravirtualized virtio devices via the "Virtio Over Channel I/O
|
||||
(virtio-ccw)" transport. This makes virtio devices discoverable via
|
||||
standard operating system algorithms for handling channel devices.
|
||||
|
||||
However this is not enough. On s390 for the majority of devices, which
|
||||
use the standard Channel I/O based mechanism, we also need to provide
|
||||
the functionality of passing through them to a Qemu virtual machine.
|
||||
the functionality of passing through them to a QEMU virtual machine.
|
||||
This includes devices that don't have a virtio counterpart (e.g. tape
|
||||
drives) or that have specific characteristics which guests want to
|
||||
exploit.
|
||||
|
||||
For passing a device to a guest, we want to use the same interface as
|
||||
everybody else, namely vfio. Thus, we would like to introduce vfio
|
||||
support for channel devices. And we would like to name this new vfio
|
||||
device "vfio-ccw".
|
||||
everybody else, namely vfio. We implement this vfio support for channel
|
||||
devices via the vfio mediated device framework and the subchannel device
|
||||
driver "vfio_ccw".
|
||||
|
||||
Access patterns of CCW devices
|
||||
------------------------------
|
||||
|
|
@ -99,7 +99,7 @@ As mentioned above, we realize vfio-ccw with a mdev implementation.
|
|||
Channel I/O does not have IOMMU hardware support, so the physical
|
||||
vfio-ccw device does not have an IOMMU level translation or isolation.
|
||||
|
||||
Sub-channel I/O instructions are all privileged instructions, When
|
||||
Subchannel I/O instructions are all privileged instructions. When
|
||||
handling the I/O instruction interception, vfio-ccw has the software
|
||||
policing and translation how the channel program is programmed before
|
||||
it gets sent to hardware.
|
||||
|
|
@ -121,7 +121,7 @@ devices:
|
|||
- The vfio_mdev driver for the mediated vfio ccw device.
|
||||
This is provided by the mdev framework. It is a vfio device driver for
|
||||
the mdev that created by vfio_ccw.
|
||||
It realize a group of vfio device driver callbacks, adds itself to a
|
||||
It realizes a group of vfio device driver callbacks, adds itself to a
|
||||
vfio group, and registers itself to the mdev framework as a mdev
|
||||
driver.
|
||||
It uses a vfio iommu backend that uses the existing map and unmap
|
||||
|
|
@ -178,7 +178,7 @@ vfio-ccw I/O region
|
|||
|
||||
An I/O region is used to accept channel program request from user
|
||||
space and store I/O interrupt result for user space to retrieve. The
|
||||
defination of the region is:
|
||||
definition of the region is:
|
||||
|
||||
struct ccw_io_region {
|
||||
#define ORB_AREA_SIZE 12
|
||||
|
|
@ -198,30 +198,23 @@ irb_area stores the I/O result.
|
|||
|
||||
ret_code stores a return code for each access of the region.
|
||||
|
||||
vfio-ccw patches overview
|
||||
-------------------------
|
||||
vfio-ccw operation details
|
||||
--------------------------
|
||||
|
||||
For now, our patches are rebased on the latest mdev implementation.
|
||||
vfio-ccw follows what vfio-pci did on the s390 paltform and uses
|
||||
vfio-iommu-type1 as the vfio iommu backend. It's a good start to launch
|
||||
the code review for vfio-ccw. Note that the implementation is far from
|
||||
complete yet; but we'd like to get feedback for the general
|
||||
architecture.
|
||||
vfio-ccw follows what vfio-pci did on the s390 platform and uses
|
||||
vfio-iommu-type1 as the vfio iommu backend.
|
||||
|
||||
* CCW translation APIs
|
||||
- Description:
|
||||
These introduce a group of APIs (start with 'cp_') to do CCW
|
||||
translation. The CCWs passed in by a user space program are
|
||||
organized with their guest physical memory addresses. These APIs
|
||||
will copy the CCWs into the kernel space, and assemble a runnable
|
||||
kernel channel program by updating the guest physical addresses with
|
||||
their corresponding host physical addresses.
|
||||
- Patches:
|
||||
vfio: ccw: introduce channel program interfaces
|
||||
A group of APIs (start with 'cp_') to do CCW translation. The CCWs
|
||||
passed in by a user space program are organized with their guest
|
||||
physical memory addresses. These APIs will copy the CCWs into kernel
|
||||
space, and assemble a runnable kernel channel program by updating the
|
||||
guest physical addresses with their corresponding host physical addresses.
|
||||
Note that we have to use IDALs even for direct-access CCWs, as the
|
||||
referenced memory can be located anywhere, including above 2G.
|
||||
|
||||
* vfio_ccw device driver
|
||||
- Description:
|
||||
The following patches utilizes the CCW translation APIs and introduce
|
||||
This driver utilizes the CCW translation APIs and introduces
|
||||
vfio_ccw, which is the driver for the I/O subchannel devices you want
|
||||
to pass through.
|
||||
vfio_ccw implements the following vfio ioctls:
|
||||
|
|
@ -236,20 +229,14 @@ architecture.
|
|||
This also provides the SET_IRQ ioctl to setup an event notifier to
|
||||
notify the user space program the I/O completion in an asynchronous
|
||||
way.
|
||||
- Patches:
|
||||
vfio: ccw: basic implementation for vfio_ccw driver
|
||||
vfio: ccw: introduce ccw_io_region
|
||||
vfio: ccw: realize VFIO_DEVICE_GET_REGION_INFO ioctl
|
||||
vfio: ccw: realize VFIO_DEVICE_RESET ioctl
|
||||
vfio: ccw: realize VFIO_DEVICE_G(S)ET_IRQ_INFO ioctls
|
||||
|
||||
The user of vfio-ccw is not limited to Qemu, while Qemu is definitely a
|
||||
The use of vfio-ccw is not limited to QEMU, while QEMU is definitely a
|
||||
good example to get understand how these patches work. Here is a little
|
||||
bit more detail how an I/O request triggered by the Qemu guest will be
|
||||
bit more detail how an I/O request triggered by the QEMU guest will be
|
||||
handled (without error handling).
|
||||
|
||||
Explanation:
|
||||
Q1-Q7: Qemu side process.
|
||||
Q1-Q7: QEMU side process.
|
||||
K1-K5: Kernel side process.
|
||||
|
||||
Q1. Get I/O region info during initialization.
|
||||
|
|
@ -263,7 +250,7 @@ Q4. Write the guest channel program and ORB to the I/O region.
|
|||
K2. Translate the guest channel program to a host kernel space
|
||||
channel program, which becomes runnable for a real device.
|
||||
K3. With the necessary information contained in the orb passed in
|
||||
by Qemu, issue the ccwchain to the device.
|
||||
by QEMU, issue the ccwchain to the device.
|
||||
K4. Return the ssch CC code.
|
||||
Q5. Return the CC code to the guest.
|
||||
|
||||
|
|
@ -271,7 +258,7 @@ Q5. Return the CC code to the guest.
|
|||
|
||||
K5. Interrupt handler gets the I/O result and write the result to
|
||||
the I/O region.
|
||||
K6. Signal Qemu to retrieve the result.
|
||||
K6. Signal QEMU to retrieve the result.
|
||||
Q6. Get the signal and event handler reads out the result from the I/O
|
||||
region.
|
||||
Q7. Update the irb for the guest.
|
||||
|
|
@ -289,10 +276,20 @@ More information for DASD and ECKD could be found here:
|
|||
https://en.wikipedia.org/wiki/Direct-access_storage_device
|
||||
https://en.wikipedia.org/wiki/Count_key_data
|
||||
|
||||
Together with the corresponding work in Qemu, we can bring the passed
|
||||
Together with the corresponding work in QEMU, we can bring the passed
|
||||
through DASD/ECKD device online in a guest now and use it as a block
|
||||
device.
|
||||
|
||||
While the current code allows the guest to start channel programs via
|
||||
START SUBCHANNEL, support for HALT SUBCHANNEL or CLEAR SUBCHANNEL is
|
||||
not yet implemented.
|
||||
|
||||
vfio-ccw supports classic (command mode) channel I/O only. Transport
|
||||
mode (HPF) is not supported.
|
||||
|
||||
QDIO subchannels are currently not supported. Classic devices other than
|
||||
DASD/ECKD might work, but have not been tested.
|
||||
|
||||
Reference
|
||||
---------
|
||||
1. ESA/s390 Principles of Operation manual (IBM Form. No. SA22-7832)
|
||||
|
|
|
|||
Loading…
Reference in New Issue