[src/trunk]: src/sys/arch/x86/x86 Call clts/stts in fpu_kern_enter/leave so t...

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/ff6093bbc672
branches:  trunk
changeset: 934042:ff6093bbc672
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Thu Jun 04 19:53:55 2020 +0000

description:
Call clts/stts in fpu_kern_enter/leave so they work.

diffstat:

 sys/arch/x86/x86/fpu.c |  19 +++++++++++++++++--
 1 files changed, 17 insertions(+), 2 deletions(-)

diffs (47 lines):

diff -r 51e33fd11516 -r ff6093bbc672 sys/arch/x86/x86/fpu.c
--- a/sys/arch/x86/x86/fpu.c    Thu Jun 04 19:50:21 2020 +0000
+++ b/sys/arch/x86/x86/fpu.c    Thu Jun 04 19:53:55 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: fpu.c,v 1.61 2020/01/31 08:55:38 maxv Exp $    */
+/*     $NetBSD: fpu.c,v 1.62 2020/06/04 19:53:55 riastradh Exp $       */
 
 /*
  * Copyright (c) 2008, 2019 The NetBSD Foundation, Inc.  All
@@ -96,7 +96,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: fpu.c,v 1.61 2020/01/31 08:55:38 maxv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: fpu.c,v 1.62 2020/06/04 19:53:55 riastradh Exp $");
 
 #include "opt_multiprocessor.h"
 
@@ -365,6 +365,14 @@
        } else {
                fpu_save_lwp(l);
        }
+
+       /*
+        * Clear CR0_TS, which fpu_save_lwp set if it saved anything --
+        * otherwise the CPU will trap if we try to use the FPU under
+        * the false impression that there has been a task switch since
+        * the last FPU usage requiring that we save the FPU state.
+        */
+       clts();
 }
 
 void
@@ -375,6 +383,13 @@
 
        KASSERT(ci->ci_ilevel == IPL_HIGH);
        KASSERT(ci->ci_kfpu_spl != -1);
+
+       /*
+        * Set CR0_TS again so that the kernel can't accidentally use
+        * the FPU.
+        */
+       stts();
+
        s = ci->ci_kfpu_spl;
        ci->ci_kfpu_spl = -1;
        splx(s);