KVM: always reload segment selectors

failed VM entry on VMX might still change %fs or %gs, thus make sure
that KVM always reloads the segment selectors. This is crutial on both
x86 and x86_64: x86 has __KERNEL_PDA in %fs on which things like
'current' depends and x86_64 has 0 there and needs MSR_GS_BASE to work.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index 25b2471..fbbf9d6 100644 (file)
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -1888,6 +1888,27 @@ again:
                [cr2]"i"(offsetof(struct kvm_vcpu, cr2))
              : "cc", "memory" );
 
+       /*
+        * Reload segment selectors ASAP. (it's needed for a functional
+        * kernel: x86 relies on having __KERNEL_PDA in %fs and x86_64
+        * relies on having 0 in %gs for the CPU PDA to work.)
+        */
+       if (fs_gs_ldt_reload_needed) {
+               load_ldt(ldt_sel);
+               load_fs(fs_sel);
+               /*
+                * If we have to reload gs, we must take care to
+                * preserve our gs base.
+                */
+               local_irq_disable();
+               load_gs(gs_sel);
+#ifdef CONFIG_X86_64
+               wrmsrl(MSR_GS_BASE, vmcs_readl(HOST_GS_BASE));
+#endif
+               local_irq_enable();
+
+               reload_tss();
+       }
        ++kvm_stat.exits;
 
        save_msrs(vcpu->guest_msrs, NR_BAD_MSRS);
@@ -1905,22 +1926,6 @@ again:
                kvm_run->exit_reason = vmcs_read32(VM_INSTRUCTION_ERROR);
                r = 0;
        } else {
-               if (fs_gs_ldt_reload_needed) {
-                       load_ldt(ldt_sel);
-                       load_fs(fs_sel);
-                       /*
-                        * If we have to reload gs, we must take care to
-                        * preserve our gs base.
-                        */
-                       local_irq_disable();
-                       load_gs(gs_sel);
-#ifdef CONFIG_X86_64
-                       wrmsrl(MSR_GS_BASE, vmcs_readl(HOST_GS_BASE));
-#endif
-                       local_irq_enable();
-
-                       reload_tss();
-               }
                /*
                 * Profile KVM exit RIPs:
                 */