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KVM: s390: Free guest debug data on vcpu destroy

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kvm_s390_clear_bp_data() is only called from
kvm_arch_vcpu_ioctl_set_guest_debug(), i.e. when user space changes or
disables debugging. A vCPU that is destroyed while hardware breakpoints
are still armed - the normal case when the VMM just exits or crashes -
leaks hw_bp_info, hw_wp_info and all old_data buffers, since generic KVM
frees the vCPU right after kvm_arch_vcpu_destroy().

That is bounded by MAX_BP_COUNT entries, so roughly 8 KiB per vCPU, but
it is unbounded over VM lifetimes. The allocations are
GFP_KERNEL_ACCOUNT, so the charge also outlives the exiting process and
pins dying memcgs.

Fix by clearing the debug data on vCPU destruction. Calling it
unconditionally is fine: struct kvm_vcpu is zero allocated, so for a vCPU
that never enabled debugging the counters are 0 and the pointers NULL.

Fixes: 27291e2165 ("KVM: s390: hardware support for guest debugging")
Cc: stable@vger.kernel.org
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20260805110455.7200-8-borntraeger@linux.ibm.com>
This commit is contained in:
Christian Borntraeger 2026-08-05 13:04:54 +02:00 committed by Claudio Imbrenda
parent a4e482def8
commit e7f698b09d
1 changed files with 1 additions and 0 deletions
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arch/s390/kvm/kvm-s390.c
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@ -3410,6 +3410,7 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
trace_kvm_s390_destroy_vcpu(vcpu->vcpu_id);
kvm_s390_clear_local_irqs(vcpu);
kvm_clear_async_pf_completion_queue(vcpu);
kvm_s390_clear_bp_data(vcpu);
if (!kvm_is_ucontrol(vcpu->kvm))
sca_del_vcpu(vcpu);
kvm_s390_update_topology_change_report(vcpu->kvm, 1);