[src/trunk]: src/sys/arch/x86/x86 Revert 1.66 "Fix race in fpu save with fpu_...

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

details:   https://anonhg.NetBSD.org/src/rev/16bd577e8945
branches:  trunk
changeset: 974027:16bd577e8945
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Mon Jul 20 16:38:47 2020 +0000

description:
Revert 1.66 "Fix race in fpu save with fpu_kern_enter in softint."

This only fixed part of the race, and we can do it more simply.

diffstat:

 sys/arch/x86/x86/fpu.c |  34 +++++-----------------------------
 1 files changed, 5 insertions(+), 29 deletions(-)

diffs (78 lines):

diff -r a29245545fcd -r 16bd577e8945 sys/arch/x86/x86/fpu.c
--- a/sys/arch/x86/x86/fpu.c    Mon Jul 20 16:37:34 2020 +0000
+++ b/sys/arch/x86/x86/fpu.c    Mon Jul 20 16:38:47 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: fpu.c,v 1.69 2020/07/20 16:37:34 riastradh Exp $       */
+/*     $NetBSD: fpu.c,v 1.70 2020/07/20 16:38:47 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 1.69 2020/07/20 16:37:34 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: fpu.c,v 1.70 2020/07/20 16:38:47 riastradh Exp $");
 
 #include "opt_multiprocessor.h"
 
@@ -126,8 +126,6 @@
 #define stts() HYPERVISOR_fpu_taskswitch(1)
 #endif
 
-static void fpu_area_do_save(void *, uint64_t);
-
 void fpu_handle_deferred(void);
 void fpu_switch(struct lwp *, struct lwp *);
 
@@ -157,24 +155,8 @@
        kpreempt_disable();
        if (l->l_md.md_flags & MDL_FPU_IN_CPU) {
                KASSERT((l->l_flag & LW_SYSTEM) == 0);
-
-               /*
-                * Order is important, in case we are interrupted and
-                * the interrupt calls fpu_kern_enter, triggering
-                * reentry of fpu_save_lwp:
-                *
-                * 1. Save FPU state.
-                * 2. Note FPU state has been saved.
-                * 3. Disable FPU access so the kernel doesn't
-                *    accidentally use it.
-                *
-                * Steps (1) and (2) are both idempotent until step
-                * (3), after which point attempting to save the FPU
-                * state will trigger #NM/fpudna fault.
-                */
-               fpu_area_do_save(area, x86_xsave_features);
+               fpu_area_save(area, x86_xsave_features);
                l->l_md.md_flags &= ~MDL_FPU_IN_CPU;
-               stts();
        }
        kpreempt_enable();
 }
@@ -263,8 +245,8 @@
        fldummy();
 }
 
-static void
-fpu_area_do_save(void *area, uint64_t xsave_features)
+void
+fpu_area_save(void *area, uint64_t xsave_features)
 {
        switch (x86_fpu_save) {
        case FPU_SAVE_FSAVE:
@@ -280,13 +262,7 @@
                xsaveopt(area, xsave_features);
                break;
        }
-}
 
-void
-fpu_area_save(void *area, uint64_t xsave_features)
-{
-
-       fpu_area_do_save(area, xsave_features);
        stts();
 }