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>

1 files changed, 21 insertions, 16 deletions

diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index 25b247199224..fbbf9d6b299f 100644
--- 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:
                  */