[ Upstream commit 0cf72f7f14 ]
The hypervisor returns migration failure if all VAS windows are not
closed. During pre-migration stage, vas_migration_handler() sets
migration_in_progress flag and closes all windows from the list.
The allocate VAS window routine checks the migration flag, setup
the window and then add it to the list. So there is possibility of
the migration handler missing the window that is still in the
process of setup.
t1: Allocate and open VAS t2: Migration event
window
lock vas_pseries_mutex
If migration_in_progress set
unlock vas_pseries_mutex
return
open window HCALL
unlock vas_pseries_mutex
Modify window HCALL lock vas_pseries_mutex
setup window migration_in_progress=true
Closes all windows from the list
// May miss windows that are
// not in the list
unlock vas_pseries_mutex
lock vas_pseries_mutex return
if nr_closed_windows == 0
// No DLPAR CPU or migration
add window to the list
// Window will be added to the
// list after the setup is completed
unlock vas_pseries_mutex
return
unlock vas_pseries_mutex
Close VAS window
// due to DLPAR CPU or migration
return -EBUSY
This patch resolves the issue with the following steps:
- Set the migration_in_progress flag without holding mutex.
- Introduce nr_open_wins_progress counter in VAS capabilities
struct
- This counter tracks the number of open windows are still in
progress
- The allocate setup window thread closes windows if the migration
is set and decrements nr_open_window_progress counter
- The migration handler waits for no in-progress open windows.
The code flow with the fix is as follows:
t1: Allocate and open VAS t2: Migration event
window
lock vas_pseries_mutex
If migration_in_progress set
unlock vas_pseries_mutex
return
open window HCALL
nr_open_wins_progress++
// Window opened, but not
// added to the list yet
unlock vas_pseries_mutex
Modify window HCALL migration_in_progress=true
setup window lock vas_pseries_mutex
Closes all windows from the list
While nr_open_wins_progress {
unlock vas_pseries_mutex
lock vas_pseries_mutex sleep
if nr_closed_windows == 0 // Wait if any open window in
or migration is not started // progress. The open window
// No DLPAR CPU or migration // thread closes the window without
add window to the list // adding to the list and return if
nr_open_wins_progress-- // the migration is in progress.
unlock vas_pseries_mutex
return
Close VAS window
nr_open_wins_progress--
unlock vas_pseries_mutex
return -EBUSY lock vas_pseries_mutex
}
unlock vas_pseries_mutex
return
Fixes: 37e6764895 ("powerpc/pseries/vas: Add VAS migration handler")
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231125235104.3405008-1-haren@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
e1b45baa2e