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authorMarc Zyngier <maz@kernel.org>2020-07-04 13:30:55 +0100
committerMarc Zyngier <maz@kernel.org>2020-07-06 11:47:02 +0100
commit146f76cc84b787c4eec6ed73ebeec708a06e4ae4 (patch)
tree36ee854a0a245d215240b0a8a263c6b91c14f1a7
parenta3f574cd65487cd993f79ab235d70229d9302c1e (diff)
downloadlinux-stericsson-146f76cc84b787c4eec6ed73ebeec708a06e4ae4.tar.gz
KVM: arm64: PMU: Fix per-CPU access in preemptible context
Commit 07da1ffaa137 ("KVM: arm64: Remove host_cpu_context member from vcpu structure") has, by removing the host CPU context pointer, exposed that kvm_vcpu_pmu_restore_guest is called in preemptible contexts: [ 266.932442] BUG: using smp_processor_id() in preemptible [00000000] code: qemu-system-aar/779 [ 266.939721] caller is debug_smp_processor_id+0x20/0x30 [ 266.944157] CPU: 2 PID: 779 Comm: qemu-system-aar Tainted: G E 5.8.0-rc3-00015-g8d4aa58b2fe3 #1374 [ 266.954268] Hardware name: amlogic w400/w400, BIOS 2020.04 05/22/2020 [ 266.960640] Call trace: [ 266.963064] dump_backtrace+0x0/0x1e0 [ 266.966679] show_stack+0x20/0x30 [ 266.969959] dump_stack+0xe4/0x154 [ 266.973338] check_preemption_disabled+0xf8/0x108 [ 266.977978] debug_smp_processor_id+0x20/0x30 [ 266.982307] kvm_vcpu_pmu_restore_guest+0x2c/0x68 [ 266.986949] access_pmcr+0xf8/0x128 [ 266.990399] perform_access+0x8c/0x250 [ 266.994108] kvm_handle_sys_reg+0x10c/0x2f8 [ 266.998247] handle_exit+0x78/0x200 [ 267.001697] kvm_arch_vcpu_ioctl_run+0x2ac/0xab8 Note that the bug was always there, it is only the switch to using percpu accessors that made it obvious. The fix is to wrap these accesses in a preempt-disabled section, so that we sample a coherent context on trap from the guest. Fixes: 435e53fb5e21 ("arm64: KVM: Enable VHE support for :G/:H perf event modifiers") Cc:: Andrew Murray <amurray@thegoodpenguin.co.uk> Signed-off-by: Marc Zyngier <maz@kernel.org>
-rw-r--r--arch/arm64/kvm/pmu.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/arch/arm64/kvm/pmu.c b/arch/arm64/kvm/pmu.c
index b5ae3a5d509e..3c224162b3dd 100644
--- a/arch/arm64/kvm/pmu.c
+++ b/arch/arm64/kvm/pmu.c
@@ -159,7 +159,10 @@ static void kvm_vcpu_pmu_disable_el0(unsigned long events)
}
/*
- * On VHE ensure that only guest events have EL0 counting enabled
+ * On VHE ensure that only guest events have EL0 counting enabled.
+ * This is called from both vcpu_{load,put} and the sysreg handling.
+ * Since the latter is preemptible, special care must be taken to
+ * disable preemption.
*/
void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu)
{
@@ -169,12 +172,14 @@ void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu)
if (!has_vhe())
return;
+ preempt_disable();
host = this_cpu_ptr(&kvm_host_data);
events_guest = host->pmu_events.events_guest;
events_host = host->pmu_events.events_host;
kvm_vcpu_pmu_enable_el0(events_guest);
kvm_vcpu_pmu_disable_el0(events_host);
+ preempt_enable();
}
/*