From 5ff92181577a89ed12ad4e0e5813751faf16a139 Mon Sep 17 00:00:00 2001 From: Claudio Imbrenda Date: Wed, 5 Jul 2023 13:19:36 +0200 Subject: [PATCH] KVM: s390: pv: simplify shutdown and fix race 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 Fixes: fb491d5500a7 ("KVM: s390: pv: asynchronous destroy for reboot") Reviewed-by: Nico Boehr Signed-off-by: Claudio Imbrenda Message-ID: <20230705111937.33472-2-imbrenda@linux.ibm.com> --- arch/s390/kvm/pv.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c index 2f34c7c..bf1fdc7 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 */ -- 2.7.4