Re: [PATCH v3 10/10] KVM: s390: Fix cleanup in kvm_s390_pv_create_cpu()

[Janosch Frank <frankja@linux.ibm.com>]

On 7/27/26 17:02, Claudio Imbrenda wrote:
> If creating a protected vCPU in kvm_s390_pv_create_cpu() fails,
> kvm_s390_pv_destroy_cpu() was called, which checks whether the vCPU has
> a PV handle and exits doing nothing otherwise. At that point, due to
> not having created the protected vCPU, the PV handle will not be set,
> and kvm_s390_pv_destroy_cpu() will do nothing, thus leaking the
> allocated memory.
> 
> Fix by factoring out the code to free and reset a PV vCPU; call it from
> kvm_s390_pv_destroy_cpu() and kvm_s390_pv_create_cpu().
> 
> Fixes: d4074324b07a ("KVM: s390: pv: avoid double free of sida page")
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> ---
>   arch/s390/kvm/pv.c | 41 +++++++++++++++++++++--------------------
>   1 file changed, 21 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
> index dc204b521052..b02e0159d3cd 100644
> --- a/arch/s390/kvm/pv.c
> +++ b/arch/s390/kvm/pv.c
> @@ -244,6 +244,24 @@ static void kvm_s390_clear_pv_state(struct kvm *kvm)
>   	kvm->arch.pv.stor_var = NULL;
>   }
>   
> +static void kvm_s390_pv_dispose_cpu(struct kvm_vcpu *vcpu, bool free_stor_base)
> +{
> +	if (free_stor_base)
> +		free_pages(vcpu->arch.pv.stor_base, get_order(uv_info.guest_cpu_stor_len));
> +	free_page((unsigned long)sida_addr(vcpu->arch.sie_block));
> +	vcpu->arch.sie_block->pv_handle_cpu = 0;
> +	vcpu->arch.sie_block->pv_handle_config = 0;
> +	memset(&vcpu->arch.pv, 0, sizeof(vcpu->arch.pv));
> +	vcpu->arch.sie_block->sdf = 0;
> +	/*
> +	 * The sidad field (for sdf == 2) is now the gbea field (for sdf == 0).
> +	 * Use the reset value of gbea to avoid leaking the kernel pointer of
> +	 * the just freed sida.
> +	 */
> +	vcpu->arch.sie_block->gbea = 1;
> +	kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
> +}
> +
>   int kvm_s390_pv_destroy_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc)
>   {
>   	int cc;
> @@ -258,24 +276,9 @@ int kvm_s390_pv_destroy_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc)
>   	WARN_ONCE(cc, "protvirt destroy cpu failed rc %x rrc %x", *rc, *rrc);
>   
>   	/* Intended memory leak for something that should never happen. */

That comment doesn't make a lot of sense anymore after your changes.