[patch] KVM: add MSR based hypercall API

Ingo Molnar
2007-01-09T09:27:05Z

Subject: [patch] KVM: add MSR based hypercall API
From: Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org>

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

VMX-only at the moment.

Signed-off-by: Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org>
---
drivers/kvm/kvm.h | 5 +++
drivers/kvm/mmu.c | 1
drivers/kvm/vmx.c | 74 +++++++++++++++++++++++++++++++++++++++++++++--
include/linux/kvm_para.h | 64 ++++++++++++++++++++++++++++++++++++++++
4 files changed, 142 insertions(+), 2 deletions(-)

Index: linux/drivers/kvm/kvm.h
===================================================================
--- linux.orig/drivers/kvm/kvm.h
+++ linux/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 +238,8 @@ struct kvm_vcpu {
unsigned long cr0;
unsigned long cr2;
unsigned long cr3;
+ struct kvm_vcpu_para_state *para_state;
+ hpa_t vm_syscall_hpa;
unsigned long cr4;
unsigned long cr8;
u64 pdptrs[4]; /* pae */
@@ -626,4 +629,6 @@ static inline u32 get_rdx_init_val(void)
#define TSS_REDIRECTION_SIZE (256 / 8)
#define RMODE_TSS_SIZE (TSS_BASE_SIZE + TSS_REDIRECTION_SIZE + TSS_IOPB_SIZE + 1)

+extern int vcpu_register_para(struct kvm_vcpu *vcpu, gpa_t para_state_gpa);
+
#endif
Index: linux/drivers/kvm/mmu.c
===================================================================
--- linux.orig/drivers/kvm/mmu.c
+++ linux/drivers/kvm/mmu.c
@@ -719,6 +719,7 @@ hpa_t gpa_to_hpa(struct kvm_vcpu *vcpu,
return ((hpa_t)page_to_pfn(page) << PAGE_SHIFT)
| (gpa & (PAGE_SIZE-1));
}
+EXPORT_SYMBOL_GPL(gpa_to_hpa);

hpa_t gva_to_hpa(struct kvm_vcpu *vcpu, gva_t gva)
{
Index: linux/drivers/kvm/vmx.c
===================================================================
--- linux.orig/drivers/kvm/vmx.c
+++ linux/drivers/kvm/vmx.c
@@ -406,10 +406,15 @@ static int vmx_set_msr(struct kvm_vcpu *
case MSR_IA32_SYSENTER_ESP:
vmcs_write32(GUEST_SYSENTER_ESP, data);
break;
- case MSR_IA32_TIME_STAMP_COUNTER: {
+ case MSR_IA32_TIME_STAMP_COUNTER:
guest_write_tsc(data);
break;
- }
+ /*
+ * This is the 'probe whether the host is KVM' logic:
+ */
+ case MSR_KVM_API_MAGIC:
+ return vcpu_register_para(vcpu, data);
+
default:
msr = find_msr_entry(vcpu, msr_index);
if (msr) {
@@ -1448,6 +1453,71 @@ static int handle_io(struct kvm_vcpu *vc
return 0;
}

+/*
+ * Register the para guest with the host:
+ */
+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, vm_syscall_hpa;
+ unsigned char *vm_syscall;
+
+ printk("KVM: guest trying to enter paravirtual mode\n");
+ printk(".... 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(".... para_state_hpa: %08Lx\n", para_state_hpa);
+ if (is_error_hpa(para_state_hpa))
+ goto err_gp;
+
+ para_state = (void *)__va(para_state_hpa);
+ printk(".... para_state_hva: %p\n", para_state);
+
+ printk(".... guest version: %d\n", para_state->guest_version);
+ printk(".... 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 = -EINVAL;
+ goto err_skip;
+ }
+
+ vm_syscall_hpa = gpa_to_hpa(vcpu, para_state->vm_syscall_addr);
+ printk(".... vm_syscall_hpa: %08Lx\n", vm_syscall_hpa);
+ if (is_error_hpa(vm_syscall_hpa)) {
+ para_state->ret = -EINVAL;
+ goto err_skip;
+ }
+
+ printk("KVM: para guest successfully registered.\n");
+ vcpu->para_state = para_state;
+ vcpu->vm_syscall_hpa = vm_syscall_hpa;
+
+ vm_syscall = __va(vm_syscall_hpa);
+ /*
+ * Patch in the VMCALL instruction:
+ */
+ vm_syscall[0] = 0x0f;
+ vm_syscall[1] = 0x01;
+ vm_syscall[2] = 0xc1;
+
+ para_state->ret = 0;
+err_skip:
+ return 0;
+err_gp:
+ return 1;
+}
+
static int handle_cr(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
{
u64 exit_qualification;
Index: linux/include/linux/kvm_para.h
===================================================================
--- /dev/null
+++ linux/include/linux/kvm_para.h
@@ -0,0 +1,64 @@
+#ifndef __LINUX_KVM_PARA_H
+#define __LINUX_KVM_PARA_H
+
+/*
+ * Guest OS interface for KVM paravirtualization
+ *
+ * Note: this interface is considered experimental and may change without
+ * notice.
+ */
+
+#define KVM_CR3_CACHE_SIZE 4
+
+struct kvm_cr3_cache_entry {
+ u64 guest_cr3;
+ u64 host_cr3;
+};
+
+struct kvm_cr3_cache {
+ struct kvm_cr3_cache_entry entry[KVM_CR3_CACHE_SIZE];
+ u32 max_idx;
+};
+
+/*
+ * 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.
+ */
+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 vm_syscall_addr;
+
+ struct kvm_cr3_cache cr3_cache;
+
+} __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
+
+#endif