[src/trunk]: src/sys/arch/x86/x86 Save fpu state at IPL_VM to exclude fpu_ker...

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

details:   https://anonhg.NetBSD.org/src/rev/483dfcc16026
branches:  trunk
changeset: 936180:483dfcc16026
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Mon Jul 20 16:41:18 2020 +0000

description:
Save fpu state at IPL_VM to exclude fpu_kern_enter/leave.

This way fpu_kern_enter/leave cannot interrupt the transition, so the
transition from state-on-CPU to state-in-memory (with TS set) is
atomic whether in an interrupt or not.

(I am not 100% convinced that this is necessary, but it makes
reasoning about the transition simpler.)

diffstat:

 sys/arch/x86/x86/fpu.c |  19 +++++++++++++------
 1 files changed, 13 insertions(+), 6 deletions(-)

diffs (65 lines):

diff -r c9da59bb1f71 -r 483dfcc16026 sys/arch/x86/x86/fpu.c
--- a/sys/arch/x86/x86/fpu.c    Mon Jul 20 16:38:47 2020 +0000
+++ b/sys/arch/x86/x86/fpu.c    Mon Jul 20 16:41:18 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: fpu.c,v 1.70 2020/07/20 16:38:47 riastradh Exp $       */
+/*     $NetBSD: fpu.c,v 1.71 2020/07/20 16:41:18 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 1.70 2020/07/20 16:38:47 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: fpu.c,v 1.71 2020/07/20 16:41:18 riastradh Exp $");
 
 #include "opt_multiprocessor.h"
 
@@ -151,14 +151,15 @@
 {
        struct pcb *pcb = lwp_getpcb(l);
        union savefpu *area = &pcb->pcb_savefpu;
+       int s;
 
-       kpreempt_disable();
+       s = splvm();
        if (l->l_md.md_flags & MDL_FPU_IN_CPU) {
                KASSERT((l->l_flag & LW_SYSTEM) == 0);
                fpu_area_save(area, x86_xsave_features);
                l->l_md.md_flags &= ~MDL_FPU_IN_CPU;
        }
-       kpreempt_enable();
+       splx(s);
 }
 
 /*
@@ -299,8 +300,12 @@
 void
 fpu_switch(struct lwp *oldlwp, struct lwp *newlwp)
 {
+       struct cpu_info *ci __diagused = curcpu();
        struct pcb *pcb;
 
+       KASSERTMSG(ci->ci_ilevel >= IPL_SCHED, "cpu%d ilevel=%d",
+           cpu_index(ci), ci->ci_ilevel);
+
        if (oldlwp->l_md.md_flags & MDL_FPU_IN_CPU) {
                KASSERT(!(oldlwp->l_flag & LW_SYSTEM));
                pcb = lwp_getpcb(oldlwp);
@@ -334,11 +339,13 @@
 void
 fpu_lwp_abandon(struct lwp *l)
 {
+       int s;
+
        KASSERT(l == curlwp);
-       kpreempt_disable();
+       s = splvm();
        l->l_md.md_flags &= ~MDL_FPU_IN_CPU;
        stts();
-       kpreempt_enable();
+       splx(s);
 }
 
 /* -------------------------------------------------------------------------- */