Re: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state transition validity
From: Kirti Wankhede
Date: Fri Sep 24 2021 - 05:37:53 EST
On 9/24/2021 1:14 PM, Shameerali Kolothum Thodi wrote:
-----Original Message-----
From: Max Gurtovoy [mailto:mgurtovoy@xxxxxxxxxx]
Sent: 23 September 2021 14:56
To: Leon Romanovsky <leon@xxxxxxxxxx>; Shameerali Kolothum Thodi
<shameerali.kolothum.thodi@xxxxxxxxxx>
Cc: Doug Ledford <dledford@xxxxxxxxxx>; Jason Gunthorpe
<jgg@xxxxxxxxxx>; Yishai Hadas <yishaih@xxxxxxxxxx>; Alex Williamson
<alex.williamson@xxxxxxxxxx>; Bjorn Helgaas <bhelgaas@xxxxxxxxxx>; David
S. Miller <davem@xxxxxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; Kirti
Wankhede <kwankhede@xxxxxxxxxx>; kvm@xxxxxxxxxxxxxxx;
linux-kernel@xxxxxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx;
linux-rdma@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; Saeed Mahameed
<saeedm@xxxxxxxxxx>
Subject: Re: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state
transition validity
On 9/23/2021 2:17 PM, Leon Romanovsky wrote:
On Thu, Sep 23, 2021 at 10:33:10AM +0000, Shameerali Kolothum Thodi
wrote:
-----Original Message-----
From: Leon Romanovsky [mailto:leon@xxxxxxxxxx]
Sent: 22 September 2021 11:39
To: Doug Ledford <dledford@xxxxxxxxxx>; Jason Gunthorpe
<jgg@xxxxxxxxxx>
Cc: Yishai Hadas <yishaih@xxxxxxxxxx>; Alex Williamson
<alex.williamson@xxxxxxxxxx>; Bjorn Helgaas <bhelgaas@xxxxxxxxxx>;
David
S. Miller <davem@xxxxxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; Kirti
Wankhede <kwankhede@xxxxxxxxxx>; kvm@xxxxxxxxxxxxxxx;
linux-kernel@xxxxxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx;
linux-rdma@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; Saeed Mahameed
<saeedm@xxxxxxxxxx>
Subject: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state
transition validity
From: Yishai Hadas <yishaih@xxxxxxxxxx>
Add an API in the core layer to check migration state transition validity
as part of a migration flow.
The valid transitions follow the expected usage as described in
uapi/vfio.h and triggered by QEMU.
This ensures that all migration implementations follow a consistent
migration state machine.
Signed-off-by: Yishai Hadas <yishaih@xxxxxxxxxx>
Reviewed-by: Kirti Wankhede <kwankhede@xxxxxxxxxx>
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxx>
---
drivers/vfio/vfio.c | 41
+++++++++++++++++++++++++++++++++++++++++
include/linux/vfio.h | 1 +
2 files changed, 42 insertions(+)
diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 3c034fe14ccb..c3ca33e513c8 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -1664,6 +1664,47 @@ static int vfio_device_fops_release(struct
inode
*inode, struct file *filep)
return 0;
}
+/**
+ * vfio_change_migration_state_allowed - Checks whether a migration
state
+ * transition is valid.
+ * @new_state: The new state to move to.
+ * @old_state: The old state.
+ * Return: true if the transition is valid.
+ */
+bool vfio_change_migration_state_allowed(u32 new_state, u32
old_state)
+{
+ enum { MAX_STATE = VFIO_DEVICE_STATE_RESUMING };
+ static const u8 vfio_from_state_table[MAX_STATE + 1][MAX_STATE +
1] = {
+ [VFIO_DEVICE_STATE_STOP] = {
+ [VFIO_DEVICE_STATE_RUNNING] = 1,
+ [VFIO_DEVICE_STATE_RESUMING] = 1,
+ },
+ [VFIO_DEVICE_STATE_RUNNING] = {
+ [VFIO_DEVICE_STATE_STOP] = 1,
+ [VFIO_DEVICE_STATE_SAVING] = 1,
+ [VFIO_DEVICE_STATE_SAVING |
VFIO_DEVICE_STATE_RUNNING]
= 1,
Do we need to allow _RESUMING state here or not? As per the "State
transitions"
section from uapi/linux/vfio.h,
It looks like we missed this state transition.
Thanks
I'm not sure this state transition is valid.
Kirti, When we would like to move from RUNNING to RESUMING ?
I guess it depends on what you report as your dev default state.
For HiSilicon ACC migration driver, we set the default to _RUNNING.
And when the migration starts, the destination side Qemu, set the
device state to _RESUMING(vfio_load_state()).
From the documentation, it looks like the assumption on default state of
the VFIO dev is _RUNNING.
That's right. in QEMU VFIO device state at init is running to maintain
backward compatibility since migration support was added later.
RUNNING -> RESUMING state transition is valid.
Thanks,
Kirti
"
* 001b => Device running, which is the default state
"
Sameerali, can you please re-test and update if you see this transition ?
Yes. And if I change the default state to _STOP, then the transition
is from _STOP --> _RESUMING.
But the documentation on State transitions doesn't have _STOP --> _RESUMING
transition as valid.
Thanks,
Shameer
" * 4. To start the resuming phase, the device state should be transitioned
from
* the _RUNNING to the _RESUMING state."
IIRC, I have seen that transition happening on the destination dev while
testing the
HiSilicon ACC dev migration.
Thanks,
Shameer
+ },
+ [VFIO_DEVICE_STATE_SAVING] = {
+ [VFIO_DEVICE_STATE_STOP] = 1,
+ [VFIO_DEVICE_STATE_RUNNING] = 1,
+ },
+ [VFIO_DEVICE_STATE_SAVING | VFIO_DEVICE_STATE_RUNNING]
= {
+ [VFIO_DEVICE_STATE_RUNNING] = 1,
+ [VFIO_DEVICE_STATE_SAVING] = 1,
+ },
+ [VFIO_DEVICE_STATE_RESUMING] = {
+ [VFIO_DEVICE_STATE_RUNNING] = 1,
+ [VFIO_DEVICE_STATE_STOP] = 1,
+ },
+ };
+
+ if (new_state > MAX_STATE || old_state > MAX_STATE)
+ return false;
+
+ return vfio_from_state_table[old_state][new_state];
+}
+EXPORT_SYMBOL_GPL(vfio_change_migration_state_allowed);
+
static long vfio_device_fops_unl_ioctl(struct file *filep,
unsigned int cmd, unsigned long arg)
{
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index b53a9557884a..e65137a708f1 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -83,6 +83,7 @@ extern struct vfio_device
*vfio_device_get_from_dev(struct device *dev);
extern void vfio_device_put(struct vfio_device *device);
int vfio_assign_device_set(struct vfio_device *device, void *set_id);
+bool vfio_change_migration_state_allowed(u32 new_state, u32
old_state);
/* events for the backend driver notify callback */
enum vfio_iommu_notify_type {
--
2.31.1