[PATCH v3] target/arm/kvm: Retry KVM_CREATE_VM call if it fails EINTR

[PATCH v3] target/arm/kvm: Retry KVM_CREATE_VM call if it fails EINTR

[Peter Maydell]

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".

v2: correctly check for -1 and errno is EINTR...
v3: really correctly check errno. This time for sure!
---
 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..1e4de9b42e3 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 == -1 && errno == EINTR);
     if (vmfd < 0) {
         goto err;
     }
-- 
2.25.1

Re: [PATCH v3] target/arm/kvm: Retry KVM_CREATE_VM call if it fails EINTR

[Vitaly Chikunov]

On Fri, Sep 30, 2022 at 12:38:24PM +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".
> 
> v2: correctly check for -1 and errno is EINTR...
> v3: really correctly check errno. This time for sure!
> ---
>  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..1e4de9b42e3 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 == -1 && errno == EINTR);

Reviewed-by: Vitaly Chikunov <vt@altlinux.org>

Thanks,

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

Re: [PATCH v3] target/arm/kvm: Retry KVM_CREATE_VM call if it fails EINTR

[Marc Zyngier]

On Fri, 30 Sep 2022 12:38:24 +0100,
Peter Maydell <peter.maydell@linaro.org> 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".
> 
> v2: correctly check for -1 and errno is EINTR...
> v3: really correctly check errno. This time for sure!
> ---
>  target/arm/kvm.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)

Acked-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.

Re: [PATCH v3] target/arm/kvm: Retry KVM_CREATE_VM call if it fails EINTR

[Eric Auger]

Hi Peter,

On 9/30/22 13:38, 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".
>
> v2: correctly check for -1 and errno is EINTR...
> v3: really correctly check errno. This time for sure!
Reviewed-by: Eric Auger <eric.auger@redhat.com>

Thanks

Eric
> ---
>  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..1e4de9b42e3 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 == -1 && errno == EINTR);
>      if (vmfd < 0) {
>          goto err;
>      }