1 files changed, 7 insertions, 0 deletions

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index a821b1cd4fa7..72bf2680f819 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -427,6 +427,13 @@ sysretl_from_sys_call:
          * cs and ss are loaded from MSRs.
          * (Note: 32bit->32bit SYSRET is different: since r11
          * does not exist, it merely sets eflags.IF=1).
+         *
+         * NB: On AMD CPUs with the X86_BUG_SYSRET_SS_ATTRS bug, the ss
+         * descriptor is not reinitialized.  This means that we must
+         * avoid SYSRET with SS == NULL, which could happen if we schedule,
+         * exit the kernel, and re-enter using an interrupt vector.  (All
+         * interrupt entries on x86_64 set SS to NULL.)  We prevent that
+         * from happening by reloading SS in __switch_to.
          */
         USERGS_SYSRET32