Re: [PATCH v2 7/7] KVM: s390: Free guest debug data on vcpu destroy

[sashiko-bot@kernel.org]

> 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: 27291e2165b6 ("KVM: s390: hardware support for guest debugging")
> Cc: stable@vger.kernel.org
> Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260804162435.28617-1-borntraeger@linux.ibm.com?part=7