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Subject[PATCH 3/3] KVM: Expose MSRs to userspace
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Date
From: Uri Lublin <uril@qumranet.com>

Expose the model-specific registers to userspace. Primarily useful for
save/resume.

Signed-off-by: Uri Lublin <uril@qumranet.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

Index: linux-2.6/drivers/kvm/kvm.h
===================================================================
--- linux-2.6.orig/drivers/kvm/kvm.h
+++ linux-2.6/drivers/kvm/kvm.h
@@ -106,11 +106,7 @@ struct vmcs {
char data[0];
};

-struct vmx_msr_entry {
- u32 index;
- u32 reserved;
- u64 data;
-};
+#define vmx_msr_entry kvm_msr_entry

struct kvm_vcpu;

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
@@ -2298,21 +2298,22 @@ static int handle_cpuid(struct kvm_vcpu
return 0;
}

-static int handle_rdmsr(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
+/*
+ * Reads an msr value (of 'msr_index') into 'pdata'.
+ * Returns 0 on success, non-0 otherwise.
+ * Assumes vcpu_load() was already called.
+ */
+static int get_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata)
{
- u32 ecx = vcpu->regs[VCPU_REGS_RCX];
- struct vmx_msr_entry *msr = find_msr_entry(vcpu, ecx);
u64 data;
+ struct vmx_msr_entry *msr;

-#ifdef KVM_DEBUG
- if (guest_cpl() != 0) {
- vcpu_printf(vcpu, "%s: not supervisor\n", __FUNCTION__);
- inject_gp(vcpu);
- return 1;
+ if (!pdata) {
+ printk(KERN_ERR "BUG: get_msr called with NULL pdata\n");
+ return -EINVAL;
}
-#endif

- switch (ecx) {
+ switch (msr_index) {
#ifdef __x86_64__
case MSR_FS_BASE:
data = vmcs_readl(GUEST_FS_BASE);
@@ -2351,11 +2352,25 @@ static int handle_rdmsr(struct kvm_vcpu
data = vcpu->apic_base;
break;
default:
- if (msr) {
- data = msr->data;
- break;
+ msr = find_msr_entry(vcpu, msr_index);
+ if (!msr) {
+ printk(KERN_ERR "kvm: unhandled rdmsr: %x\n", msr_index);
+ return 1;
}
- printk(KERN_ERR "kvm: unhandled rdmsr: %x\n", ecx);
+ data = msr->data;
+ break;
+ }
+
+ *pdata = data;
+ return 0;
+}
+
+static int handle_rdmsr(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
+{
+ u32 ecx = vcpu->regs[VCPU_REGS_RCX];
+ u64 data;
+
+ if (get_msr(vcpu, ecx, &data)) {
inject_gp(vcpu);
return 1;
}
@@ -2401,22 +2416,16 @@ static void set_efer(struct kvm_vcpu *vc

#endif

-static int handle_wrmsr(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
+
+/*
+ * Writes msr value into into the appropriate "register".
+ * Returns 0 on success, non-0 otherwise.
+ * Assumes vcpu_load() was already called.
+ */
+static int set_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data)
{
- u32 ecx = vcpu->regs[VCPU_REGS_RCX];
struct vmx_msr_entry *msr;
- u64 data = (vcpu->regs[VCPU_REGS_RAX] & -1u)
- | ((u64)(vcpu->regs[VCPU_REGS_RDX] & -1u) << 32);
-
-#ifdef KVM_DEBUG
- if (guest_cpl() != 0) {
- vcpu_printf(vcpu, "%s: not supervisor\n", __FUNCTION__);
- inject_gp(vcpu);
- return 1;
- }
-#endif
-
- switch (ecx) {
+ switch (msr_index) {
#ifdef __x86_64__
case MSR_FS_BASE:
vmcs_writel(GUEST_FS_BASE, data);
@@ -2437,7 +2446,7 @@ static int handle_wrmsr(struct kvm_vcpu
#ifdef __x86_64
case MSR_EFER:
set_efer(vcpu, data);
- return 1;
+ break;
case MSR_IA32_MC0_STATUS:
printk(KERN_WARNING "%s: MSR_IA32_MC0_STATUS 0x%llx, nop\n"
, __FUNCTION__, data);
@@ -2455,16 +2464,31 @@ static int handle_wrmsr(struct kvm_vcpu
vcpu->apic_base = data;
break;
default:
- msr = find_msr_entry(vcpu, ecx);
- if (msr) {
- msr->data = data;
- break;
+ msr = find_msr_entry(vcpu, msr_index);
+ if (!msr) {
+ printk(KERN_ERR "kvm: unhandled wrmsr: 0x%x\n", msr_index);
+ return 1;
}
- printk(KERN_ERR "kvm: unhandled wrmsr: %x\n", ecx);
+ msr->data = data;
+ break;
+ }
+
+ return 0;
+}
+
+static int handle_wrmsr(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
+{
+ u32 ecx = vcpu->regs[VCPU_REGS_RCX];
+ u64 data = (vcpu->regs[VCPU_REGS_RAX] & -1u)
+ | ((u64)(vcpu->regs[VCPU_REGS_RDX] & -1u) << 32);
+
+ if (set_msr(vcpu, ecx, data) != 0) {
inject_gp(vcpu);
return 1;
}
- skip_emulated_instruction(vcpu);
+
+ if (ecx != MSR_EFER)
+ skip_emulated_instruction(vcpu);
return 1;
}

@@ -3121,6 +3145,125 @@ static int kvm_dev_ioctl_set_sregs(struc
}

/*
+ * List of msr numbers which we expose to userspace through KVM_GET_MSRS
+ * and KVM_SET_MSRS.
+ */
+static u32 msrs_to_save[] = {
+ MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
+ MSR_K6_STAR,
+#ifdef __x86_64__
+ MSR_CSTAR, MSR_KERNEL_GS_BASE, MSR_SYSCALL_MASK, MSR_LSTAR,
+#endif
+ MSR_IA32_TIME_STAMP_COUNTER,
+};
+
+static int kvm_dev_ioctl_get_msrs(struct kvm *kvm, struct kvm_msrs *msrs)
+{
+ struct kvm_vcpu *vcpu;
+ struct kvm_msr_entry *entry, *entries;
+ int rc;
+ u32 size, num_entries, i;
+
+ if (msrs->vcpu < 0 || msrs->vcpu >= KVM_MAX_VCPUS)
+ return -EINVAL;
+
+ num_entries = ARRAY_SIZE(msrs_to_save);
+ if (msrs->nmsrs < num_entries) {
+ /* inform actual number of entries */
+ msrs->nmsrs = num_entries;
+ return -EINVAL;
+ }
+
+ vcpu = vcpu_load(kvm, msrs->vcpu);
+ if (!vcpu)
+ return -ENOENT;
+
+ msrs->nmsrs = num_entries; /* update to actual number of entries */
+ size = msrs->nmsrs * sizeof(struct kvm_msr_entry);
+ rc = -E2BIG;
+ if (size > 4096)
+ goto out_vcpu;
+
+ rc = -ENOMEM;
+ entries = vmalloc(size);
+ if (entries == NULL)
+ goto out_vcpu;
+
+ memset(entries, 0, size);
+ rc = -EINVAL;
+ for (i=0; i<num_entries; i++) {
+ entry = &entries[i];
+ entry->index = msrs_to_save[i];
+ if (get_msr(vcpu, entry->index, &entry->data))
+ goto out_free;
+ }
+
+ rc = -EFAULT;
+ if (copy_to_user(msrs->entries, entries, size))
+ goto out_free;
+
+ rc = 0;
+out_free:
+ vfree(entries);
+
+out_vcpu:
+ vcpu_put(vcpu);
+
+ return rc;
+}
+
+static int kvm_dev_ioctl_set_msrs(struct kvm *kvm, struct kvm_msrs *msrs)
+{
+ struct kvm_vcpu *vcpu;
+ struct kvm_msr_entry *entry, *entries;
+ int rc;
+ u32 size, num_entries, i;
+
+ if (msrs->vcpu < 0 || msrs->vcpu >= KVM_MAX_VCPUS)
+ return -EINVAL;
+
+ num_entries = ARRAY_SIZE(msrs_to_save);
+ if (msrs->nmsrs < num_entries) {
+ msrs->nmsrs = num_entries; /* inform actual size */
+ return -EINVAL;
+ }
+
+ vcpu = vcpu_load(kvm, msrs->vcpu);
+ if (!vcpu)
+ return -ENOENT;
+
+ size = msrs->nmsrs * sizeof(struct kvm_msr_entry);
+ rc = -E2BIG;
+ if (size > 4096)
+ goto out_vcpu;
+
+ rc = -ENOMEM;
+ entries = vmalloc(size);
+ if (entries == NULL)
+ goto out_vcpu;
+
+ rc = -EFAULT;
+ if (copy_from_user(entries, msrs->entries, size))
+ goto out_free;
+
+ rc = -EINVAL;
+ for (i=0; i<num_entries; i++) {
+ entry = &entries[i];
+ if (set_msr(vcpu, entry->index, entry->data))
+ goto out_free;
+ }
+
+ rc = 0;
+out_free:
+ vfree(entries);
+
+out_vcpu:
+ vcpu_put(vcpu);
+
+ return rc;
+}
+
+/*
* Translate a guest virtual address to a guest physical address.
*/
static int kvm_dev_ioctl_translate(struct kvm *kvm, struct kvm_translation *tr)
@@ -3361,6 +3504,33 @@ static long kvm_dev_ioctl(struct file *f
goto out;
break;
}
+ case KVM_GET_MSRS: {
+ struct kvm_msrs kvm_msrs;
+
+ r = -EFAULT;
+ if (copy_from_user(&kvm_msrs, (void *)arg, sizeof kvm_msrs))
+ goto out;
+ r = kvm_dev_ioctl_get_msrs(kvm, &kvm_msrs);
+ if (r)
+ goto out;
+ r = -EFAULT;
+ if (copy_to_user((void *)arg, &kvm_msrs, sizeof kvm_msrs))
+ goto out;
+ r = 0;
+ break;
+ }
+ case KVM_SET_MSRS: {
+ struct kvm_msrs kvm_msrs;
+
+ r = -EFAULT;
+ if (copy_from_user(&kvm_msrs, (void *)arg, sizeof kvm_msrs))
+ goto out;
+ r = kvm_dev_ioctl_set_msrs(kvm, &kvm_msrs);
+ if (r)
+ goto out;
+ r = 0;
+ break;
+ }
default:
;
}
Index: linux-2.6/include/linux/kvm.h
===================================================================
--- linux-2.6.orig/include/linux/kvm.h
+++ linux-2.6/include/linux/kvm.h
@@ -141,6 +141,23 @@ struct kvm_sregs {
__u64 interrupt_bitmap[KVM_IRQ_BITMAP_SIZE(__u64)];
};

+struct kvm_msr_entry {
+ __u32 index;
+ __u32 reserved;
+ __u64 data;
+};
+
+/* for KVM_GET_MSRS and KVM_SET_MSRS */
+struct kvm_msrs {
+ __u32 vcpu;
+ __u32 nmsrs; /* number of msrs in entries */
+
+ union {
+ struct kvm_msr_entry __user *entries;
+ __u64 padding;
+ };
+};
+
/* for KVM_TRANSLATE */
struct kvm_translation {
/* in */
@@ -200,5 +217,7 @@ struct kvm_dirty_log {
#define KVM_SET_MEMORY_REGION _IOW(KVMIO, 10, struct kvm_memory_region)
#define KVM_CREATE_VCPU _IOW(KVMIO, 11, int /* vcpu_slot */)
#define KVM_GET_DIRTY_LOG _IOW(KVMIO, 12, struct kvm_dirty_log)
+#define KVM_GET_MSRS _IOWR(KVMIO, 13, struct kvm_msrs)
+#define KVM_SET_MSRS _IOW(KVMIO, 14, struct kvm_msrs)

#endif
-
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