From: Oleg Nesterov <oleg@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Fenghua Yu <fenghua.yu@intel.com>,
Suresh Siddha <sbsiddha@gmail.com>,
Bean Anderson <bean@azulsystems.com>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
the arch/x86 maintainers <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: [PATCH 2/4] x86, fpu: don't abuse ->has_fpu in __kernel_fpu_begin/end
Date: Fri, 29 Aug 2014 20:16:32 +0200 [thread overview]
Message-ID: <20140829181632.GC30659@redhat.com> (raw)
In-Reply-To: <20140829181533.GA30659@redhat.com>
Now that we have in_kernel_fpu we can remove __thread_clear_has_fpu()
in __kernel_fpu_begin(). And this allow to replace the asymmetrical
and nontrivial use_eager_fpu+tsk_used_math check in kernel_fpu_end()
with the same __thread_has_fpu().
The logic becomes really simple afaics: if _begin() does save() then
_end() needs restore(), and this is controlled by __thread_has_fpu().
Also, with this patch __kernel_fpu_end() does restore_fpu_checking()
and WARNs if it fails instead of math_state_restore(). I think this
looks better because we no longer need __thread_fpu_begin(), and it
would be better to report the failure in this case.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
arch/x86/kernel/i387.c | 19 ++++++-------------
1 files changed, 6 insertions(+), 13 deletions(-)
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index 8fb8868..19dd36d 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -82,9 +82,7 @@ void __kernel_fpu_begin(void)
/* FIXME: race with math_state_restore()-like code */
if (__thread_has_fpu(me)) {
- __thread_clear_has_fpu(me);
__save_init_fpu(me);
- /* We do 'stts()' in __kernel_fpu_end() */
} else if (!use_eager_fpu()) {
this_cpu_write(fpu_owner_task, NULL);
clts();
@@ -94,17 +92,12 @@ EXPORT_SYMBOL(__kernel_fpu_begin);
void __kernel_fpu_end(void)
{
- if (use_eager_fpu()) {
- /*
- * For eager fpu, most the time, tsk_used_math() is true.
- * Restore the user math as we are done with the kernel usage.
- * At few instances during thread exit, signal handling etc,
- * tsk_used_math() is false. Those few places will take proper
- * actions, so we don't need to restore the math here.
- */
- if (likely(tsk_used_math(current)))
- math_state_restore();
- } else {
+ struct task_struct *me = current;
+
+ if (__thread_has_fpu(me)) {
+ if (WARN_ON(restore_fpu_checking(me)))
+ drop_init_fpu(me);
+ } else if (!use_eager_fpu()) {
stts();
}
--
1.5.5.1
next prev parent reply other threads:[~2014-08-29 18:19 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-27 18:51 [PATCH 0/4] x86, fpu: copy_process's FPU paths cleanups Oleg Nesterov
2014-08-27 18:51 ` [PATCH 1/4] x86, fpu: change __thread_fpu_begin() to use use_eager_fpu() Oleg Nesterov
2014-08-27 18:51 ` [PATCH 2/4] x86, fpu: copy_process: avoid fpu_alloc/copy if !used_math() Oleg Nesterov
2014-08-27 18:52 ` [PATCH 3/4] x86, fpu: copy_process: sanitize fpu->last_cpu initialization Oleg Nesterov
2014-08-27 18:52 ` [PATCH 4/4] x86, fpu: shift "fpu_counter = 0" from copy_thread() to arch_dup_task_struct() Oleg Nesterov
2014-08-27 20:43 ` [PATCH 0/4] x86, fpu: copy_process's FPU paths cleanups H. Peter Anvin
2014-08-28 6:50 ` Ingo Molnar
2014-08-28 12:25 ` Oleg Nesterov
2014-08-28 10:38 ` Oleg Nesterov
2014-08-28 1:17 ` Linus Torvalds
2014-08-28 11:16 ` Oleg Nesterov
2014-08-29 18:15 ` [PATCH 0/4] x86, fpu: kernel_fpu_begin/end cleanups Oleg Nesterov
2014-08-29 18:16 ` [PATCH 1/4] x86, fpu: introduce per-cpu "bool in_kernel_fpu" Oleg Nesterov
2014-09-02 6:43 ` Suresh Siddha
2014-08-29 18:16 ` Oleg Nesterov [this message]
2014-08-29 18:17 ` [PATCH 3/4] x86, fpu: irq_fpu_usable: always return true if use_eager_fpu() Oleg Nesterov
2014-08-29 18:17 ` [PATCH 4/4] x86, fpu: irq_fpu_usable: kill all checks except !in_kernel_fpu Oleg Nesterov
2014-09-02 7:04 ` Suresh Siddha
2014-09-02 12:58 ` Oleg Nesterov
2014-09-02 14:13 ` Oleg Nesterov
2014-09-02 5:04 ` [PATCH 0/4] x86, fpu: copy_process's FPU paths cleanups Suresh Siddha
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