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

[Cornelia Huck <cohuck@redhat.com>]

On Tue, Oct 17 2023, Peter Maydell <peter.maydell@linaro.org> wrote:

> 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.

Whoops, it seems that I misread this. (And my test environment didn't
have that enabled...)