Introduce a new pre_restart notifier chain for callbacks that need to be executed after the system has been made quiescent with syscore_shutdown(), before machine restart.
Register pre-restart notifiers to flush pmem areas from CPU data cache to memory on reboot, immediately before restarting the machine. This ensures all other CPUs are quiescent before the pmem data is flushed to memory. The use-case for this new notifier chain is to preserve tracing data within pmem areas on systems where the BIOS does not clear memory across warm reboots. I did an earlier POC that flushed caches on panic/die oops notifiers [1], but it did not cover the reboot case. I've been made aware that some distribution vendors have started shipping their own modified version of my earlier POC patch. This makes a strong argument for upstreaming this work. Link: https://lore.kernel.org/linux-kernel/[email protected]/ [1] Cc: Vishal Verma <[email protected]> Cc: Dave Jiang <[email protected]> Cc: Ira Weiny <[email protected]> Cc: [email protected] Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Dave Hansen <[email protected]> Cc: [email protected] Cc: "H. Peter Anvin" <[email protected]> Cc: Catalin Marinas <[email protected]> Cc: Will Deacon <[email protected]> Cc: [email protected] Mathieu Desnoyers (4): kernel/reboot: Introduce pre_restart notifiers nvdimm/pmem: Flush to memory before machine restart arm64: Invoke pre_restart notifiers x86: Invoke pre_restart notifiers arch/arm64/kernel/process.c | 2 ++ arch/x86/kernel/reboot.c | 7 +++-- drivers/nvdimm/pmem.c | 29 ++++++++++++++++++++- drivers/nvdimm/pmem.h | 2 ++ include/linux/reboot.h | 4 +++ kernel/reboot.c | 51 +++++++++++++++++++++++++++++++++++++ 6 files changed, 92 insertions(+), 3 deletions(-) -- 2.39.2
