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>

diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index 9a49b2e..fd7746a 100644 (file)
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -14,6 +14,7 @@
 
 #include "vmx.h"
 #include <linux/kvm.h>
+#include <linux/kvm_para.h>
 
 #define CR0_PE_MASK (1ULL << 0)
 #define CR0_TS_MASK (1ULL << 3)
@@ -237,6 +238,9 @@ struct kvm_vcpu {
        unsigned long cr0;
        unsigned long cr2;
        unsigned long cr3;
+       gpa_t para_state_gpa;
+       struct page *para_state_page;
+       gpa_t hypercall_gpa;
        unsigned long cr4;
        unsigned long cr8;
        u64 pdptrs[4]; /* pae */
@@ -382,6 +386,8 @@ struct kvm_arch_ops {
        int (*run)(struct kvm_vcpu *vcpu, struct kvm_run *run);
        int (*vcpu_setup)(struct kvm_vcpu *vcpu);
        void (*skip_emulated_instruction)(struct kvm_vcpu *vcpu);
+       void (*patch_hypercall)(struct kvm_vcpu *vcpu,
+                               unsigned char *hypercall_addr);
 };
 
 extern struct kvm_stat kvm_stat;

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 122c05f..757a41f 100644 (file)
--- 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;

diff --git a/drivers/kvm/svm.c b/drivers/kvm/svm.c
index 72cac04..f6e8652 100644 (file)
--- a/drivers/kvm/svm.c
+++ b/drivers/kvm/svm.c
@@ -1669,6 +1669,18 @@ static int is_disabled(void)
        return 0;
 }
 
+static void
+svm_patch_hypercall(struct kvm_vcpu *vcpu, unsigned char *hypercall)
+{
+       /*
+        * Patch in the VMMCALL instruction:
+        */
+       hypercall[0] = 0x0f;
+       hypercall[1] = 0x01;
+       hypercall[2] = 0xd9;
+       hypercall[3] = 0xc3;
+}
+
 static struct kvm_arch_ops svm_arch_ops = {
        .cpu_has_kvm_support = has_svm,
        .disabled_by_bios = is_disabled,
@@ -1717,6 +1729,7 @@ static struct kvm_arch_ops svm_arch_ops = {
        .run = svm_vcpu_run,
        .skip_emulated_instruction = skip_emulated_instruction,
        .vcpu_setup = svm_vcpu_setup,
+       .patch_hypercall = svm_patch_hypercall,
 };
 
 static int __init svm_init(void)

diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index d1198e2..0198d40 100644 (file)
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -1469,6 +1469,18 @@ static int handle_io(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
        return 0;
 }
 
+static void
+vmx_patch_hypercall(struct kvm_vcpu *vcpu, unsigned char *hypercall)
+{
+       /*
+        * Patch in the VMCALL instruction:
+        */
+       hypercall[0] = 0x0f;
+       hypercall[1] = 0x01;
+       hypercall[2] = 0xc1;
+       hypercall[3] = 0xc3;
+}
+
 static int handle_cr(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 {
        u64 exit_qualification;
@@ -2064,6 +2076,7 @@ static struct kvm_arch_ops vmx_arch_ops = {
        .run = vmx_vcpu_run,
        .skip_emulated_instruction = skip_emulated_instruction,
        .vcpu_setup = vmx_vcpu_setup,
+       .patch_hypercall = vmx_patch_hypercall,
 };
 
 static int __init vmx_init(void)

diff --git a/include/linux/kvm_para.h b/include/linux/kvm_para.h
new file mode 100644 (file)
index 0000000..74be5c1
--- /dev/null
+++ b/include/linux/kvm_para.h
@@ -0,0 +1,55 @@
+#ifndef __LINUX_KVM_PARA_H
+#define __LINUX_KVM_PARA_H
+
+/*
+ * Guest OS interface for KVM paravirtualization
+ *
+ * Note: this interface is totally experimental, and is certain to change
+ *       as we make progress.
+ */
+
+/*
+ * Per-VCPU descriptor area shared between guest and host. Writable to
+ * both guest and host. Registered with the host by the guest when
+ * a guest acknowledges paravirtual mode.
+ *
+ * NOTE: all addresses are guest-physical addresses (gpa), to make it
+ * easier for the hypervisor to map between the various addresses.
+ */
+struct kvm_vcpu_para_state {
+       /*
+        * API version information for compatibility. If there's any support
+        * mismatch (too old host trying to execute too new guest) then
+        * the host will deny entry into paravirtual mode. Any other
+        * combination (new host + old guest and new host + new guest)
+        * is supposed to work - new host versions will support all old
+        * guest API versions.
+        */
+       u32 guest_version;
+       u32 host_version;
+       u32 size;
+       u32 ret;
+
+       /*
+        * The address of the vm exit instruction (VMCALL or VMMCALL),
+        * which the host will patch according to the CPU model the
+        * VM runs on:
+        */
+       u64 hypercall_gpa;
+
+} __attribute__ ((aligned(PAGE_SIZE)));
+
+#define KVM_PARA_API_VERSION 1
+
+/*
+ * This is used for an RDMSR's ECX parameter to probe for a KVM host.
+ * Hopefully no CPU vendor will use up this number. This is placed well
+ * out of way of the typical space occupied by CPU vendors' MSR indices,
+ * and we think (or at least hope) it wont be occupied in the future
+ * either.
+ */
+#define MSR_KVM_API_MAGIC 0x87655678
+
+#define KVM_EINVAL 1
+
+#endif