This is a generic interface to find out what you can use
KVM_GET_ONE_REG/KVM_SET_ONE_REG on.  Archs need to define
KVM_HAVE_REG_LIST and then kvm_arch_num_regs() and
kvm_arch_copy_reg_indices() functions.

It's inspired by KVM_GET_MSR_INDEX_LIST, except it's a per-vcpu ioctl,
and uses 64-bit indices.

Signed-off-by: Rusty Russell <rusty.russ...@linaro.org>
---
 Documentation/virtual/kvm/api.txt |   20 ++++++++++++++++++++
 include/linux/kvm.h               |   12 ++++++++++++
 include/linux/kvm_host.h          |    5 ++++-
 virt/kvm/kvm_main.c               |   20 ++++++++++++++++++++
 4 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/Documentation/virtual/kvm/api.txt 
b/Documentation/virtual/kvm/api.txt
index b91bfd4..f30c3d0 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1985,6 +1985,26 @@ the virtualized real-mode area (VRMA) facility, the 
kernel will
 re-create the VMRA HPTEs on the next KVM_RUN of any vcpu.)
 
 
+4.76 KVM_VCPU_GET_REG_LIST
+
+Capability: KVM_CAP_REG_LIST
+Architectures: all
+Type: vcpu ioctl
+Parameters: struct kvm_reg_list (in/out)
+Returns: 0 on success; -1 on error
+Errors:
+  E2BIG:     the reg index list is too big to fit in the array specified by
+             the user (the number required will be written into n).
+
+struct kvm_reg_list {
+       __u64 n; /* number of registers in reg[] */
+       __u64 reg[0];
+};
+
+This ioctl returns the guest registers that are supported for the
+KVM_GET_ONE_REG/KVM_SET_ONE_REG calls.
+
+
 5. The kvm_run structure
 ------------------------
 
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 8c3760e..e839889 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -625,6 +625,7 @@ struct kvm_ppc_smmu_info {
 #ifdef __KVM_HAVE_READONLY_MEM
 #define KVM_CAP_READONLY_MEM 81
 #endif
+#define KVM_CAP_REG_LIST 82
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -913,6 +914,7 @@ struct kvm_s390_ucas_mapping {
 #define KVM_SET_ONE_REG                  _IOW(KVMIO,  0xac, struct kvm_one_reg)
 /* VM is being stopped by host */
 #define KVM_KVMCLOCK_CTRL        _IO(KVMIO,   0xad)
+#define KVM_VCPU_GET_REG_LIST    _IOWR(KVMIO, 0xb0, struct kvm_reg_list)
 
 #define KVM_DEV_ASSIGN_ENABLE_IOMMU    (1 << 0)
 #define KVM_DEV_ASSIGN_PCI_2_3         (1 << 1)
@@ -964,4 +971,9 @@ struct kvm_assigned_msix_entry {
        __u16 padding[3];
 };
 
+/* For KVM_VCPU_GET_REG_LIST. */
+struct kvm_reg_list {
+       __u64 n; /* number of regs */
+       __u64 reg[0];
+};
 #endif /* __LINUX_KVM_H */
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 2277ff8..d9ee33f 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -587,7 +587,10 @@ int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu);
 int kvm_arch_get_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg);
 int kvm_arch_set_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg);
 #endif
-
+#ifdef KVM_HAVE_REG_LIST
+unsigned long kvm_arch_num_regs(struct kvm_vcpu *vcpu);
+int kvm_arch_copy_reg_indices(struct kvm_vcpu *vcpu, u64 __user *indices);
+#endif
 void kvm_free_physmem(struct kvm *kvm);
 
 void *kvm_kvzalloc(unsigned long size);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 169a001..453fe93 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2082,6 +2082,23 @@ out_free2:
                break;
        }
 #endif
+#ifdef KVM_HAVE_REG_LIST
+       case KVM_VCPU_GET_REG_LIST: {
+               struct kvm_reg_list __user *user_list = argp;
+               struct kvm_reg_list reg_list;
+               unsigned n;
+
+               if (copy_from_user(&reg_list, user_list, sizeof reg_list))
+                       return -EFAULT;
+               n = reg_list.n;
+               reg_list.n = kvm_arch_num_regs(vcpu);
+               if (copy_to_user(user_list, &reg_list, sizeof reg_list))
+                       return -EFAULT;
+               if (n < reg_list.n)
+                       return -E2BIG;
+               return kvm_arch_copy_reg_indices(vcpu, user_list->reg);
+       }
+#endif
 
        default:
                r = kvm_arch_vcpu_ioctl(filp, ioctl, arg);
@@ -2397,6 +2414,9 @@ static long kvm_dev_ioctl_check_extension_generic(long 
arg)
 #ifdef KVM_HAVE_ONE_REG
        case KVM_CAP_ONE_REG:
 #endif
+#ifdef KVM_HAVE_REG_LIST
+       case KVM_CAP_REG_LIST:
+#endif
                return 1;
 #ifdef KVM_CAP_IRQ_ROUTING
        case KVM_CAP_IRQ_ROUTING:
-- 
1.7.9.5

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