[PATCH] KVM: Do not export unsupported msrs to userspace

Some msrs, such as MSR_STAR, are not available on all processors.  Exporting
them causes qemu to try to fetch them, which will fail.

So, check all msrs for validity at module load time.

Signed-off-by: Michael Riepe <michael@mr511.de>
Signed-off-by: Avi Kivity <avi@qumranet.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 24 insertions, 3 deletions

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 4621b4ee6744..bc2e6c19f855 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -1417,6 +1417,9 @@ static int kvm_dev_ioctl_set_sregs(struct kvm *kvm, struct kvm_sregs *sregs)
 /*
  * List of msr numbers which we expose to userspace through KVM_GET_MSRS
  * and KVM_SET_MSRS, and KVM_GET_MSR_INDEX_LIST.
+ *
+ * This list is modified at module load time to reflect the
+ * capabilities of the host cpu.
  */
 static u32 msrs_to_save[] = {
         MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
@@ -1427,6 +1430,22 @@ static u32 msrs_to_save[] = {
         MSR_IA32_TIME_STAMP_COUNTER,
 };
 
+static unsigned num_msrs_to_save;
+
+static __init void kvm_init_msr_list(void)
+{
+        u32 dummy[2];
+        unsigned i, j;
+
+        for (i = j = 0; i < ARRAY_SIZE(msrs_to_save); i++) {
+                if (rdmsr_safe(msrs_to_save[i], &dummy[0], &dummy[1]) < 0)
+                        continue;
+                if (j < i)
+                        msrs_to_save[j] = msrs_to_save[i];
+                j++;
+        }
+        num_msrs_to_save = j;
+}
 
 /*
  * Adapt set_msr() to msr_io()'s calling convention
@@ -1735,15 +1754,15 @@ static long kvm_dev_ioctl(struct file *filp,
                 if (copy_from_user(&msr_list, user_msr_list, sizeof msr_list))
                         goto out;
                 n = msr_list.nmsrs;
-                msr_list.nmsrs = ARRAY_SIZE(msrs_to_save);
+                msr_list.nmsrs = num_msrs_to_save;
                 if (copy_to_user(user_msr_list, &msr_list, sizeof msr_list))
                         goto out;
                 r = -E2BIG;
-                if (n < ARRAY_SIZE(msrs_to_save))
+                if (n < num_msrs_to_save)
                         goto out;
                 r = -EFAULT;
                 if (copy_to_user(user_msr_list->indices, &msrs_to_save,
-                                 sizeof msrs_to_save))
+                                 num_msrs_to_save * sizeof(u32)))
                         goto out;
                 r = 0;
         }
@@ -1894,6 +1913,8 @@ static __init int kvm_init(void)
 
         kvm_init_debug();
 
+        kvm_init_msr_list();
+
         if ((bad_page = alloc_page(GFP_KERNEL)) == NULL) {
                 r = -ENOMEM;
                 goto out;