Re: [Qemu-devel] [PATCH v2 12/14] target/arm/kvm: scratch vcpu: Preserve input kvm_vcpu_init features

[Auger Eric <eric.auger@redhat.com>]

Hi Drew,

On 6/21/19 6:34 PM, Andrew Jones wrote:
> kvm_arm_create_scratch_host_vcpu() takes a struct kvm_vcpu_init
> parameter. Rather than just using it as an output parameter to
> pass back the preferred target, use it also as an input parameter,
> allowing a caller to pass a selected target if they wish and to
> also pass cpu features. If the caller doesn't want to select a
> target they can pass -1 for the target which indicates they want
> to use the preferred target and have it passed back like before.
> 
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> ---
>  target/arm/kvm.c   | 20 +++++++++++++++-----
>  target/arm/kvm32.c |  6 +++++-
>  target/arm/kvm64.c |  6 +++++-
>  3 files changed, 25 insertions(+), 7 deletions(-)
> 
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index 60645a196d3d..66c0c198604a 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -64,7 +64,7 @@ bool kvm_arm_create_scratch_host_vcpu(const uint32_t *cpus_to_try,
>                                        int *fdarray,
>                                        struct kvm_vcpu_init *init)
>  {
> -    int ret, kvmfd = -1, vmfd = -1, cpufd = -1;
> +    int ret = 0, kvmfd = -1, vmfd = -1, cpufd = -1;
>  
>      kvmfd = qemu_open("/dev/kvm", O_RDWR);
>      if (kvmfd < 0) {
> @@ -84,7 +84,14 @@ bool kvm_arm_create_scratch_host_vcpu(const uint32_t *cpus_to_try,
>          goto finish;
>      }
>  
> -    ret = ioctl(vmfd, KVM_ARM_PREFERRED_TARGET, init);
> +    if (init->target == -1) {
> +        struct kvm_vcpu_init preferred;
> +
> +        ret = ioctl(vmfd, KVM_ARM_PREFERRED_TARGET, &preferred);
> +        if (!ret) {
> +            init->target = preferred.target;
wouldn't it be safe to copy the whole struct. Kernel code says:
        /*
         * For now, we don't return any features.
         * In future, we might use features to return target
         * specific features available for the preferred
         * target type.
         */

> +        }
> +    }
>      if (ret >= 0) {
>          ret = ioctl(cpufd, KVM_ARM_VCPU_INIT, init);
>          if (ret < 0) {
> @@ -96,10 +103,12 @@ bool kvm_arm_create_scratch_host_vcpu(const uint32_t *cpus_to_try,
>           * creating one kind of guest CPU which is its preferred
>           * CPU type.
>           */
> +        struct kvm_vcpu_init try;
> +
>          while (*cpus_to_try != QEMU_KVM_ARM_TARGET_NONE) {
> -            init->target = *cpus_to_try++;
> -            memset(init->features, 0, sizeof(init->features));
> -            ret = ioctl(cpufd, KVM_ARM_VCPU_INIT, init);
> +            try.target = *cpus_to_try++;
> +            memcpy(try.features, init->features, sizeof(init->features));
> +            ret = ioctl(cpufd, KVM_ARM_VCPU_INIT, &try);
>              if (ret >= 0) {
>                  break;
>              }
> @@ -107,6 +116,7 @@ bool kvm_arm_create_scratch_host_vcpu(const uint32_t *cpus_to_try,
>          if (ret < 0) {
>              goto err;
>          }
> +        init->target = try.target;
>      } else {
>          /* Treat a NULL cpus_to_try argument the same as an empty
>           * list, which means we will fail the call since this must
> diff --git a/target/arm/kvm32.c b/target/arm/kvm32.c
> index 51f78f722b18..d007f6bd34d7 100644
> --- a/target/arm/kvm32.c
> +++ b/target/arm/kvm32.c
> @@ -54,7 +54,11 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
>          QEMU_KVM_ARM_TARGET_CORTEX_A15,
>          QEMU_KVM_ARM_TARGET_NONE
>      };
> -    struct kvm_vcpu_init init;
> +    /*
> +     * target = -1 informs kvm_arm_create_scratch_host_vcpu()
> +     * to use the preferred target
> +     */
> +    struct kvm_vcpu_init init = { .target = -1, };
>  
>      if (!kvm_arm_create_scratch_host_vcpu(cpus_to_try, fdarray, &init)) {
>          return false;
> diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
> index 9fc7f078cf68..2821135a4d0e 100644
> --- a/target/arm/kvm64.c
> +++ b/target/arm/kvm64.c
> @@ -502,7 +502,11 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
>          KVM_ARM_TARGET_CORTEX_A57,
>          QEMU_KVM_ARM_TARGET_NONE
>      };
> -    struct kvm_vcpu_init init;
> +    /*
> +     * target = -1 informs kvm_arm_create_scratch_host_vcpu()
> +     * to use the preferred target
> +     */
> +    struct kvm_vcpu_init init = { .target = -1, };
>  
>      if (!kvm_arm_create_scratch_host_vcpu(cpus_to_try, fdarray, &init)) {
>          return false;
> 

Besides

Reviewed-by: Eric Auger <eric.auger@redhat.com>

Thanks

Eric