On 1/26/26 16:21, Stanislav Kinsburskii wrote:
On Mon, Jan 26, 2026 at 03:07:18PM -0800, Mukesh R wrote:
On 1/26/26 12:43, Stanislav Kinsburskii wrote:
On Mon, Jan 26, 2026 at 12:20:09PM -0800, Mukesh R wrote:
On 1/25/26 14:39, Stanislav Kinsburskii wrote:
On Fri, Jan 23, 2026 at 04:16:33PM -0800, Mukesh R wrote:
On 1/23/26 14:20, Stanislav Kinsburskii wrote:
The MSHV driver deposits kernel-allocated pages to the hypervisor during
runtime and never withdraws them. This creates a fundamental incompatibility
with KEXEC, as these deposited pages remain unavailable to the new kernel
loaded via KEXEC, leading to potential system crashes upon kernel accessing
hypervisor deposited pages.
Make MSHV mutually exclusive with KEXEC until proper page lifecycle
management is implemented.
Signed-off-by: Stanislav Kinsburskii <[email protected]>
---
drivers/hv/Kconfig | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
index 7937ac0cbd0f..cfd4501db0fa 100644
--- a/drivers/hv/Kconfig
+++ b/drivers/hv/Kconfig
@@ -74,6 +74,7 @@ config MSHV_ROOT
# e.g. When withdrawing memory, the hypervisor gives back 4k pages in
# no particular order, making it impossible to reassemble larger pages
depends on PAGE_SIZE_4KB
+ depends on !KEXEC
select EVENTFD
select VIRT_XFER_TO_GUEST_WORK
select HMM_MIRROR
Will this affect CRASH kexec? I see few CONFIG_CRASH_DUMP in kexec.c
implying that crash dump might be involved. Or did you test kdump
and it was fine?
Yes, it will. Crash kexec depends on normal kexec functionality, so it
will be affected as well.
So not sure I understand the reason for this patch. We can just block
kexec if there are any VMs running, right? Doing this would mean any
further developement would be without a ver important and major feature,
right?
This is an option. But until it's implemented and merged, a user mshv
driver gets into a situation where kexec is broken in a non-obvious way.
The system may crash at any time after kexec, depending on whether the
new kernel touches the pages deposited to hypervisor or not. This is a
bad user experience.
I understand that. But with this we cannot collect core and debug any
crashes. I was thinking there would be a quick way to prohibit kexec
for update via notifier or some other quick hack. Did you already
explore that and didn't find anything, hence this?
This quick hack you mention isn't quick in the upstream kernel as there
is no hook to interrupt kexec process except the live update one.
That's the one we want to interrupt and block right? crash kexec
is ok and should be allowed. We can document we don't support kexec
for update for now.
I sent an RFC for that one but given todays conversation details is
won't be accepted as is.
Are you taking about this?
"mshv: Add kexec safety for deposited pages"
Making mshv mutually exclusive with kexec is the only viable option for
now given time constraints.
It is intended to be replaced with proper page lifecycle management in
the future.
Yeah, that could take a long time and imo we cannot just disable KEXEC
completely. What we want is just block kexec for updates from some
mshv file for now, we an print during boot that kexec for updates is
not supported on mshv. Hope that makes sense.
Thanks,
-Mukesh
Thanks,
Stanislav
Thanks,
-Mukesh
Therefor it should be explicitly forbidden as it's essentially not
supported yet.
Thanks,
Stanislav
Thanks,
Stanislav
Thanks,
-Mukesh
