KVM: Be more careful restoring fs on lightweight vmexit

i386 wants fs for accessing the pda even on a lightweight exit, so ensure
we can always restore it.  This fixes a regression on i386 introduced by
the lightweight vmexit patch.

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

diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index 9ebb18d..49cadd3 100644 (file)
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -1832,16 +1832,21 @@ preempted:
         * Set host fs and gs selectors.  Unfortunately, 22.2.3 does not
         * allow segment selectors with cpl > 0 or ti == 1.
         */
-       fs_sel = read_fs();
-       gs_sel = read_gs();
        ldt_sel = read_ldt();
-       fs_gs_ldt_reload_needed = (fs_sel & 7) | (gs_sel & 7) | ldt_sel;
-       if (!fs_gs_ldt_reload_needed) {
+       fs_gs_ldt_reload_needed = ldt_sel;
+       fs_sel = read_fs();
+       if (!(fs_sel & 7))
                vmcs_write16(HOST_FS_SELECTOR, fs_sel);
-               vmcs_write16(HOST_GS_SELECTOR, gs_sel);
-       } else {
+       else {
                vmcs_write16(HOST_FS_SELECTOR, 0);
+               fs_gs_ldt_reload_needed = 1;
+       }
+       gs_sel = read_gs();
+       if (!(gs_sel & 7))
+               vmcs_write16(HOST_GS_SELECTOR, gs_sel);
+       else {
                vmcs_write16(HOST_GS_SELECTOR, 0);
+               fs_gs_ldt_reload_needed = 1;
        }
 
 #ifdef CONFIG_X86_64
@@ -2035,11 +2040,6 @@ again:
        }
 
 out:
-       /*
-        * 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);