Re: [PATCH v2 3/3] arm/kvm: convert to read_sys_reg64

[Peter Maydell]

On Tue, 10 Oct 2023 at 15:25, Cornelia Huck <cohuck@redhat.com> wrote:
>
> We can use read_sys_reg64 to get the SVE_VLS register instead of
> calling GET_ONE_REG directly.
>
> Suggested-by: Gavin Shan <gshan@redhat.com>
> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> ---
>  target/arm/kvm64.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
>
> diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
> index 558c0b88dd69..d40c89a84752 100644
> --- a/target/arm/kvm64.c
> +++ b/target/arm/kvm64.c
> @@ -500,10 +500,6 @@ uint32_t kvm_arm_sve_get_vls(CPUState *cs)
>              .target = -1,
>              .features[0] = (1 << KVM_ARM_VCPU_SVE),
>          };
> -        struct kvm_one_reg reg = {
> -            .id = KVM_REG_ARM64_SVE_VLS,
> -            .addr = (uint64_t)&vls[0],
> -        };
>          int fdarray[3], ret;
>
>          probed = true;
> @@ -512,7 +508,7 @@ uint32_t kvm_arm_sve_get_vls(CPUState *cs)
>              error_report("failed to create scratch VCPU with SVE enabled");
>              abort();
>          }
> -        ret = ioctl(fdarray[2], KVM_GET_ONE_REG, &reg);
> +        ret = read_sys_reg64(fdarray[2], &vls[0], KVM_REG_ARM64_SVE_VLS);
>          kvm_arm_destroy_scratch_host_vcpu(fdarray);
>          if (ret) {
>              error_report("failed to get KVM_REG_ARM64_SVE_VLS: %s",

read_sys_reg64() asserts that the register you're trying to
read is 64 bits, but KVM_REG_ARM64_SVE_VLS is not, it's 512 bits:

#define KVM_REG_ARM64_SVE_VLS           (KVM_REG_ARM64 | KVM_REG_ARM64_SVE | \
                                         KVM_REG_SIZE_U512 | 0xffff)

So this change would trip the assert on a host where SVE
is supported and enabled.

thanks
-- PMM