Re: [PATCH v4 3/4] KVM: s390: avoid kvm_s390_handle_pv() error overwrite

Lorenzo Stoakes (Oracle)
2026-03-23T17:53:27Z

On Sat, Mar 21, 2026 at 10:43:07PM -0700, Suren Baghdasaryan wrote:
> If kvm_s390_handle_pv() call fails its error code gets recorded but
> execution proceeds as if the call was successful. If the next call to
> copy_to_user() fails then the original error is overwritten.

Is that really a big deal though, as you're returning an error in either case?

> The follow-up patch adds fatal signal checks during VMA walk, which
> makes it possible for kvm_s390_handle_pv() to return EINTR error.
> Without this fix any error including EINTR can be overwritten and
> original error will be lost.
>
> Change error handling for kvm_s390_handle_pv() to alter normal flow
> once failure happens. This is consistent with how kvm_arch_vm_ioctl
> handles errors for other ioctl commands.
>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
> arch/s390/kvm/kvm-s390.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 3eb60aa932ec..ddad08c0926f 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -2947,6 +2947,8 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
> }
> /* must be called without kvm->lock */
> r = kvm_s390_handle_pv(kvm, &args);
> + if (r)
> + break;
> if (copy_to_user(argp, &args, sizeof(args))) {

Yeah as per Sashiko we probably need to copy_to_user() still.

But in that case, do we even need a change at all? I'm not sure it really
matters which error code terminates things does it?

> r = -EFAULT;
> break;
> --
> 2.53.0.1018.g2bb0e51243-goog
>

Thanks, Lorenzo