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Fix race in fpu save with fpu_kern_enter in softint. 

Likely source of:

https://mail-index.netbsd.org/current-users/2020/07/02/msg039051.html
This commit is contained in:
riastradh 2020-07-06 01:08:15 +00:00
parent 7036a82e3b
commit 4ecb7e6b96
1 changed files with 29 additions and 5 deletions
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34
sys/arch/x86/x86/fpu.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: fpu.c,v 1.65 2020/06/14 16:12:05 riastradh Exp $ */
/* $NetBSD: fpu.c,v 1.66 2020/07/06 01:08:15 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 1.65 2020/06/14 16:12:05 riastradh Exp $");
__KERNEL_RCSID(0, "$NetBSD: fpu.c,v 1.66 2020/07/06 01:08:15 riastradh Exp $");
#include "opt_multiprocessor.h"
@ -126,6 +126,8 @@ __KERNEL_RCSID(0, "$NetBSD: fpu.c,v 1.65 2020/06/14 16:12:05 riastradh Exp $");
#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 *);
@ -155,8 +157,24 @@ fpu_save_lwp(struct lwp *l)
kpreempt_disable();
if (l->l_md.md_flags & MDL_FPU_IN_CPU) {
KASSERT((l->l_flag & LW_SYSTEM) == 0);
fpu_area_save(area, x86_xsave_features);
/*
* 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);
l->l_md.md_flags &= ~MDL_FPU_IN_CPU;
stts();
}
kpreempt_enable();
}
@ -245,8 +263,8 @@ fpu_errata_amd(void)
fldummy();
}
void
fpu_area_save(void *area, uint64_t xsave_features)
static void
fpu_area_do_save(void *area, uint64_t xsave_features)
{
switch (x86_fpu_save) {
case FPU_SAVE_FSAVE:
@ -262,7 +280,13 @@ fpu_area_save(void *area, uint64_t xsave_features)
xsaveopt(area, xsave_features);
break;
}
}
void
fpu_area_save(void *area, uint64_t xsave_features)
{
fpu_area_do_save(area, xsave_features);
stts();
}