Re: [PATCH 04/59] KVM: arm64: nv: Introduce nested virtualization VCPU feature

Marc Zyngier
2019-07-03T11:56:59Z

On 24/06/2019 12:43, Dave Martin wrote:
> On Fri, Jun 21, 2019 at 10:37:48AM +0100, Marc Zyngier wrote:
>> From: Christoffer Dall <christoffer.dall@arm.com>
>>
>> Introduce the feature bit and a primitive that checks if the feature is
>> set behind a static key check based on the cpus_have_const_cap check.
>>
>> Checking nested_virt_in_use() on systems without nested virt enabled
>> should have neglgible overhead.
>>
>> We don't yet allow userspace to actually set this feature.
>>
>> Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>> ---
>
> [...]
>
>> diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
>> new file mode 100644
>> index 000000000000..8a3d121a0b42
>> --- /dev/null
>> +++ b/arch/arm64/include/asm/kvm_nested.h
>> @@ -0,0 +1,13 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +#ifndef __ARM64_KVM_NESTED_H
>> +#define __ARM64_KVM_NESTED_H
>> +
>> +#include <linux/kvm_host.h>
>> +
>> +static inline bool nested_virt_in_use(const struct kvm_vcpu *vcpu)
>> +{
>> + return cpus_have_const_cap(ARM64_HAS_NESTED_VIRT) &&
>> + test_bit(KVM_ARM_VCPU_NESTED_VIRT, vcpu->arch.features);
>> +}
>
> Also, is it worth having a vcpu->arch.flags flag for this, similarly to
> SVE and ptrauth?

What would we expose through this flag?

Thanks,

M.
--
Jazz is not dead. It just smells funny...