Re: [PATCH] target/arm/kvm: Retry KVM_CREATE_VM call if it fails EINTR

[Vitaly Chikunov]

Peter,

On Mon, Sep 26, 2022 at 02:36:44PM +0100, Peter Maydell wrote:
> Occasionally the KVM_CREATE_VM ioctl can return EINTR, even though
> there is no pending signal to be taken. In commit 94ccff13382055
> we added a retry-on-EINTR loop to the KVM_CREATE_VM call in the
> generic KVM code. Adopt the same approach for the use of the
> ioctl in the Arm-specific KVM code (where we use it to create a
> scratch VM for probing for various things).
> 
> For more information, see the mailing list thread:
> https://lore.kernel.org/qemu-devel/8735e0s1zw.wl-maz@kernel.org/
> 
> Reported-by: Vitaly Chikunov <vt@altlinux.org>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> The view in the thread seems to be that this is a kernel bug (because
> in QEMU's case there shouldn't be a signal to be delivered at this
> point because of our signal handling strategy); so I've adopted the
> same "just retry-on-EINTR for this specific ioctl" approach that
> commit 94ccff13 did, rather than, for instance, something wider like
> "make kvm_ioctl() and friends always retry on EINTR".
> ---
>  target/arm/kvm.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index e5c1bd50d29..2982d216176 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -79,7 +79,9 @@ bool kvm_arm_create_scratch_host_vcpu(const uint32_t 
> *cpus_to_try,
>      if (max_vm_pa_size < 0) {
>          max_vm_pa_size = 0;
>      }
> -    vmfd = ioctl(kvmfd, KVM_CREATE_VM, max_vm_pa_size);
> +    do {
> +        vmfd = ioctl(kvmfd, KVM_CREATE_VM, max_vm_pa_size);
> +    } while (vmfd == -EINTR);

This does not seem correct. ioctl(2) returns -1 on error and will set errno
to EINTR (in this case).

Thanks,

>      if (vmfd < 0) {
>          goto err;
>      }
> -- 
> 2.25.1