KVM: add MSR based hypercall API

This adds a special MSR based hypercall API to KVM. This is to be
used by paravirtual kernels and virtual drivers.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 73 insertions, 0 deletions

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 122c05f283e1..757a41f1db84 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -1204,6 +1204,73 @@ void realmode_set_cr(struct kvm_vcpu *vcpu, int cr, unsigned long val,
         }
 }
 
+/*
+ * Register the para guest with the host:
+ */
+static int vcpu_register_para(struct kvm_vcpu *vcpu, gpa_t para_state_gpa)
+{
+        struct kvm_vcpu_para_state *para_state;
+        hpa_t para_state_hpa, hypercall_hpa;
+        struct page *para_state_page;
+        unsigned char *hypercall;
+        gpa_t hypercall_gpa;
+
+        printk(KERN_DEBUG "kvm: guest trying to enter paravirtual mode\n");
+        printk(KERN_DEBUG ".... para_state_gpa: %08Lx\n", para_state_gpa);
+
+        /*
+         * Needs to be page aligned:
+         */
+        if (para_state_gpa != PAGE_ALIGN(para_state_gpa))
+                goto err_gp;
+
+        para_state_hpa = gpa_to_hpa(vcpu, para_state_gpa);
+        printk(KERN_DEBUG ".... para_state_hpa: %08Lx\n", para_state_hpa);
+        if (is_error_hpa(para_state_hpa))
+                goto err_gp;
+
+        para_state_page = pfn_to_page(para_state_hpa >> PAGE_SHIFT);
+        para_state = kmap_atomic(para_state_page, KM_USER0);
+
+        printk(KERN_DEBUG "....  guest version: %d\n", para_state->guest_version);
+        printk(KERN_DEBUG "....           size: %d\n", para_state->size);
+
+        para_state->host_version = KVM_PARA_API_VERSION;
+        /*
+         * We cannot support guests that try to register themselves
+         * with a newer API version than the host supports:
+         */
+        if (para_state->guest_version > KVM_PARA_API_VERSION) {
+                para_state->ret = -KVM_EINVAL;
+                goto err_kunmap_skip;
+        }
+
+        hypercall_gpa = para_state->hypercall_gpa;
+        hypercall_hpa = gpa_to_hpa(vcpu, hypercall_gpa);
+        printk(KERN_DEBUG ".... hypercall_hpa: %08Lx\n", hypercall_hpa);
+        if (is_error_hpa(hypercall_hpa)) {
+                para_state->ret = -KVM_EINVAL;
+                goto err_kunmap_skip;
+        }
+
+        printk(KERN_DEBUG "kvm: para guest successfully registered.\n");
+        vcpu->para_state_page = para_state_page;
+        vcpu->para_state_gpa = para_state_gpa;
+        vcpu->hypercall_gpa = hypercall_gpa;
+
+        hypercall = kmap_atomic(pfn_to_page(hypercall_hpa >> PAGE_SHIFT),
+                                KM_USER1) + (hypercall_hpa & ~PAGE_MASK);
+        kvm_arch_ops->patch_hypercall(vcpu, hypercall);
+        kunmap_atomic(hypercall, KM_USER1);
+
+        para_state->ret = 0;
+err_kunmap_skip:
+        kunmap_atomic(para_state, KM_USER0);
+        return 0;
+err_gp:
+        return 1;
+}
+
 int kvm_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
 {
         u64 data;
@@ -1312,6 +1379,12 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
         case MSR_IA32_MISC_ENABLE:
                 vcpu->ia32_misc_enable_msr = data;
                 break;
+        /*
+         * This is the 'probe whether the host is KVM' logic:
+         */
+        case MSR_KVM_API_MAGIC:
+                return vcpu_register_para(vcpu, data);
+
         default:
                 printk(KERN_ERR "kvm: unhandled wrmsr: 0x%x\n", msr);
                 return 1;