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SubjectRe: [PATCH v1] KVM: x86: add KVM_CAP_DEVICE_CTRL
On Thu, Dec 15, 2022, Wei Wang wrote:
> KVM_CAP_DEVICE_CTRL allows userspace to create emulated device in KVM.
> For example, userspace VFIO implementation needs to create a kvm_device
> (i.e. KVM_DEV_TYPE_VFIO) on x86. So add the cap to allow userspace for
> such use cases.
>
> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> ---
> arch/x86/kvm/x86.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 69227f77b201..1cdc4469652c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4410,6 +4410,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> case KVM_CAP_VAPIC:
> case KVM_CAP_ENABLE_CAP:
> case KVM_CAP_VM_DISABLE_NX_HUGE_PAGES:
> + case KVM_CAP_DEVICE_CTRL:

Rather than hardcode this in x86, I think it would be better to add an #ifdef'd
version in the generic check. E.g. if MIPS or RISC-V ever gains KVM_VFIO support
then they'll need to enumerate KVM_CAP_DEVICE_CTRL too, and odds are we'll forget
to to do.

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 13e88297f999..f70b9cea95d9 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4525,6 +4525,10 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
case KVM_CAP_BINARY_STATS_FD:
case KVM_CAP_SYSTEM_EVENT_DATA:
return 1;
+#ifdef CONFIG_KVM_VFIO
+ case KVM_CAP_DEVICE_CTRL:
+ return 1;
+#endif
default:
break;
}
The other potentially bad idea would be to detect the presence of a device_ops and
delete all of the arch hooks, e.g.

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 9c5573bc4614..190e9c3b10a7 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -212,7 +212,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
r = vgic_present;
break;
case KVM_CAP_IOEVENTFD:
- case KVM_CAP_DEVICE_CTRL:
case KVM_CAP_USER_MEMORY:
case KVM_CAP_SYNC_MMU:
case KVM_CAP_DESTROY_MEMORY_REGION_WORKS:
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 04494a4fb37a..21f9fbe96f6a 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -541,7 +541,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_ENABLE_CAP:
case KVM_CAP_ONE_REG:
case KVM_CAP_IOEVENTFD:
- case KVM_CAP_DEVICE_CTRL:
case KVM_CAP_IMMEDIATE_EXIT:
case KVM_CAP_SET_GUEST_DEBUG:
r = 1;
diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
index 65a964d7e70d..6efe93b282e1 100644
--- a/arch/riscv/kvm/vm.c
+++ b/arch/riscv/kvm/vm.c
@@ -57,7 +57,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)

switch (ext) {
case KVM_CAP_IOEVENTFD:
- case KVM_CAP_DEVICE_CTRL:
case KVM_CAP_USER_MEMORY:
case KVM_CAP_SYNC_MMU:
case KVM_CAP_DESTROY_MEMORY_REGION_WORKS:
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index e4890e04b210..191d220b6a30 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -567,7 +567,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_ENABLE_CAP:
case KVM_CAP_S390_CSS_SUPPORT:
case KVM_CAP_IOEVENTFD:
- case KVM_CAP_DEVICE_CTRL:
case KVM_CAP_S390_IRQCHIP:
case KVM_CAP_VM_ATTRIBUTES:
case KVM_CAP_MP_STATE:
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 13e88297f999..99e3da9ce42d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4525,6 +4525,15 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
case KVM_CAP_BINARY_STATS_FD:
case KVM_CAP_SYSTEM_EVENT_DATA:
return 1;
+ case KVM_CAP_DEVICE_CTRL: {
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(kvm_device_ops_table); ++) {
+ if (kvm_device_ops_table[i])
+ return 1;
+ }
+ return 0;
+ }
default:
break;
}


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