Re: [PATCH v3 33/66] KVM: arm64: nv: Support multiple nested Stage-2 mmu structures

On Thu, 21 Jan 2021 02:59:13 +0000,
Haibo Xu [off-list ref] wrote:

On Fri, 11 Dec 2020 at 00:04, Marc Zyngier [off-list ref] wrote:

[...]

quoted

diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index 9fb44bc7db3f..8e85d2ef24d9 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c

@@ -19,12 +19,177 @@
 #include <linux/kvm.h>
 #include <linux/kvm_host.h>

+#include <asm/kvm_arm.h>
 #include <asm/kvm_emulate.h>
+#include <asm/kvm_mmu.h>
 #include <asm/kvm_nested.h>
 #include <asm/sysreg.h>

 #include "sys_regs.h"

+void kvm_init_nested(struct kvm *kvm)
+{
+       kvm->arch.nested_mmus = NULL;
+       kvm->arch.nested_mmus_size = 0;
+}
+
+int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu)
+{
+       struct kvm *kvm = vcpu->kvm;
+       struct kvm_s2_mmu *tmp;
+       int num_mmus;
+       int ret = -ENOMEM;
+
+       if (!test_bit(KVM_ARM_VCPU_HAS_EL2, vcpu->arch.features))
+               return 0;
+
+       if (!cpus_have_final_cap(ARM64_HAS_NESTED_VIRT))
+               return -EINVAL;

nit: returning a "not supported" kind of errno?

I think this is consistent with what we otherwise return when there is
a mismatch between requested features from userspace and host
capabilities (such as asking for a 32bit guest on a 64bit only CPU).

What seems to be missing though is a way to *advertise* the feature to
userspace as such:

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 97d377265d8e..0225b81d3434 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c

@@ -243,6 +243,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_ARM_EL1_32BIT:
 		r = cpus_have_const_cap(ARM64_HAS_32BIT_EL1);
 		break;
+	case KVM_CAP_ARM_EL2:
+		r = cpus_have_const_cap(ARM64_HAS_NESTED_VIRT);
+		break;
 	case KVM_CAP_GUEST_DEBUG_HW_BPS:
 		r = get_num_brps();
 		break;

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 374c67875cdb..555a60ac00d8 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h

@@ -1058,6 +1058,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_ENFORCE_PV_FEATURE_CPUID 190
 #define KVM_CAP_SYS_HYPERV_CPUID 191
 #define KVM_CAP_DIRTY_LOG_RING 192
+#define KVM_CAP_ARM_EL2 193
 
 #ifdef KVM_CAP_IRQ_ROUTING
 

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.