This is a note to let you know that I've just added the patch titled
KVM: s390: pv: simplify shutdown and fix race
to the 6.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kvm-s390-pv-simplify-shutdown-and-fix-race.patch
and it can be found in the queue-6.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 469d3ac7321990f1b8d55049f86b6b5d2de0705c
Author: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Date: Wed Jul 5 13:19:36 2023 +0200
KVM: s390: pv: simplify shutdown and fix race
[ Upstream commit 5ff92181577a89ed12ad4e0e5813751faf16a139 ]
Simplify the shutdown of non-protected VMs. There is no need to do
complex manipulations of the counter if it was zero.
This also fixes a very rare race which caused pages to be torn down
from the address space with a non-zero counter even on older machines
that don't support the UVC instruction, causing a crash.
Reported-by: Marc Hartmayer <mhartmay@xxxxxxxxxxxxx>
Fixes: fb491d5500a7 ("KVM: s390: pv: asynchronous destroy for reboot")
Reviewed-by: Nico Boehr <nrb@xxxxxxxxxxxxx>
Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Message-ID: <20230705111937.33472-2-imbrenda@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
index 3ce5f4351156a..899f3b8ac0110 100644
--- a/arch/s390/kvm/pv.c
+++ b/arch/s390/kvm/pv.c
@@ -411,8 +411,12 @@ int kvm_s390_pv_deinit_cleanup_all(struct kvm *kvm, u16 *rc, u16 *rrc)
u16 _rc, _rrc;
int cc = 0;
- /* Make sure the counter does not reach 0 before calling s390_uv_destroy_range */
- atomic_inc(&kvm->mm->context.protected_count);
+ /*
+ * Nothing to do if the counter was already 0. Otherwise make sure
+ * the counter does not reach 0 before calling s390_uv_destroy_range.
+ */
+ if (!atomic_inc_not_zero(&kvm->mm->context.protected_count))
+ return 0;
*rc = 1;
/* If the current VM is protected, destroy it */
