From: Marc Zyngier maz@kernel.org
commit 970dee09b230895fe2230d2b32ad05a2826818c6 upstream.
Since 0bf50497f03b ("KVM: Drop kvm_count_lock and instead protect kvm_usage_count with kvm_lock"), hotplugging back a CPU whilst a guest is running results in a number of ugly splats as most of this code expects to run with preemption disabled, which isn't the case anymore.
While the context is preemptable, it isn't migratable, which should be enough. But we have plenty of preemptible() checks all over the place, and our per-CPU accessors also disable preemption.
Since this affects released versions, let's do the easy fix first, disabling preemption in kvm_arch_hardware_enable(). We can always revisit this with a more invasive fix in the future.
Fixes: 0bf50497f03b ("KVM: Drop kvm_count_lock and instead protect kvm_usage_count with kvm_lock") Reported-by: Kristina Martsenko kristina.martsenko@arm.com Tested-by: Kristina Martsenko kristina.martsenko@arm.com Signed-off-by: Marc Zyngier maz@kernel.org Link: https://lore.kernel.org/r/aeab7562-2d39-e78e-93b1-4711f8cc3fa5@arm.com Cc: stable@vger.kernel.org # v6.3, v6.4 Link: https://lore.kernel.org/r/20230703163548.1498943-1-maz@kernel.org Signed-off-by: Oliver Upton oliver.upton@linux.dev Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/kvm/arm.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
--- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -1793,8 +1793,17 @@ static void _kvm_arch_hardware_enable(vo
int kvm_arch_hardware_enable(void) { - int was_enabled = __this_cpu_read(kvm_arm_hardware_enabled); + int was_enabled;
+ /* + * Most calls to this function are made with migration + * disabled, but not with preemption disabled. The former is + * enough to ensure correctness, but most of the helpers + * expect the later and will throw a tantrum otherwise. + */ + preempt_disable(); + + was_enabled = __this_cpu_read(kvm_arm_hardware_enabled); _kvm_arch_hardware_enable(NULL);
if (!was_enabled) { @@ -1802,6 +1811,8 @@ int kvm_arch_hardware_enable(void) kvm_timer_cpu_up(); }
+ preempt_enable(); + return 0; }