Re: Re: [PATCH v7 4/4] RISC-V: KVM: add KVM_CAP_RISCV_SET_HGATP_MODE

[fangyu . yu]

>> From: Fangyu Yu <fangyu.yu@xxxxxxxxxxxxxxxxx>
>>
>> Add a VM capability that allows userspace to select the G-stage page table
>> format by setting HGATP.MODE on a per-VM basis.
>>
>> Userspace enables the capability via KVM_ENABLE_CAP, passing the requested
>> HGATP.MODE in args[0]. The request is rejected with -EINVAL if the mode is
>> not supported by the host, and with -EBUSY if the VM has already been
>> committed (e.g. vCPUs have been created or any memslot is populated).
>>
>> KVM_CHECK_EXTENSION(KVM_CAP_RISCV_SET_HGATP_MODE) returns a bitmask of the
>> HGATP.MODE formats supported by the host.
>>
>> Signed-off-by: Fangyu Yu <fangyu.yu@xxxxxxxxxxxxxxxxx>
>> Reviewed-by: Andrew Jones <andrew.jones@xxxxxxxxxxxxxxxx>
>> Reviewed-by: Guo Ren <guoren@xxxxxxxxxx>
>> ---
>> diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
>> @@ -211,12 +214,23 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>>
>>  int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
>>  {
>> +	case KVM_CAP_RISCV_SET_HGATP_MODE:
>> +		if (!kvm_riscv_hgatp_mode_is_valid(cap->args[0]))
>> +			return -EINVAL;
>> +
>> +		if (kvm->created_vcpus || !kvm_are_all_memslots_empty(kvm))
>> +			return -EBUSY;
>
>Since multiple VM ioctls can execute concurrently, I would protect
>created_vcpus by kvm->lock and kvm_are_all_memslots_empty by
>kvm->slots_lock.
>

Agreed. I’ll protect created_vcpus with kvm->lock and call
kvm_are_all_memslots_empty() under kvm->slots_lock, following the
kvm->lock -> kvm->slots_lock ordering in v8.

Thanks,
Fangyu

>Thanks.