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KVM: s390: pv: simplify shutdown and fix race

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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@linux.ibm.com>
Fixes: fb491d5500 ("KVM: s390: pv: asynchronous destroy for reboot")
Reviewed-by: Nico Boehr <nrb@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20230705111937.33472-2-imbrenda@linux.ibm.com>
This commit is contained in:
Claudio Imbrenda 2023-07-05 13:19:36 +02:00
parent fdf0eaf114
commit 5ff9218157
1 changed files with 6 additions and 2 deletions
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8
arch/s390/kvm/pv.c
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@ -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 */