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Subject[PATCH 7/13] KVM: add MSR based hypercall API
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From: Ingo Molnar <mingo@elte.hu>

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>

Index: linux-2.6/drivers/kvm/kvm_main.c
===================================================================
--- linux-2.6.orig/drivers/kvm/kvm_main.c
+++ linux-2.6/drivers/kvm/kvm_main.c
@@ -1204,6 +1204,73 @@ void realmode_set_cr(struct kvm_vcpu *vc
}
}

+/*
+ * 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 *
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;
Index: linux-2.6/drivers/kvm/kvm.h
===================================================================
--- linux-2.6.orig/drivers/kvm/kvm.h
+++ linux-2.6/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;
Index: linux-2.6/include/linux/kvm_para.h
===================================================================
--- /dev/null
+++ linux-2.6/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
Index: linux-2.6/drivers/kvm/svm.c
===================================================================
--- linux-2.6.orig/drivers/kvm/svm.c
+++ linux-2.6/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)
Index: linux-2.6/drivers/kvm/vmx.c
===================================================================
--- linux-2.6.orig/drivers/kvm/vmx.c
+++ linux-2.6/drivers/kvm/vmx.c
@@ -1469,6 +1469,18 @@ static int handle_io(struct kvm_vcpu *vc
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)
-
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