From: Oleg Nesterov <oleg@redhat.com>
To: "H. Peter Anvin" <hpa@zytor.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Cc: Chuck Ebbert <chuckebbert.lk@gmail.com>,
Jan Kratochvil <jan.kratochvil@redhat.com>,
linux-kernel@vger.kernel.org
Subject: ptrace && fpu_lazy_restore
Date: Sun, 15 Apr 2012 01:52:38 +0200 [thread overview]
Message-ID: <20120414235238.GA11131@redhat.com> (raw)
Credits to Jan and Chuck, see
https://bugzilla.redhat.com/show_bug.cgi?id=810668
with reproducer:
https://bugzilla.redhat.com/attachment.cgi?id=577270
But afaics the root of the problem is clear. Once PTRACE_SETFPREGS
changes fpu.state->fxsave the task obviously needs restore_fpu_checking()
on context switch.
But I am not sure about the fix, and in any case I need more time
to read this new code.
Oleg.
--- x/arch/x86/kernel/i387.c~ 2012-04-09 20:12:12.000000000 +0200
+++ x/arch/x86/kernel/i387.c 2012-04-15 01:34:09.000000000 +0200
@@ -301,6 +301,8 @@ int xfpregs_set(struct task_struct *targ
sanitize_i387_state(target);
+ target->thread.fpu.last_cpu = ~0;
+
ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
&target->thread.fpu.state->fxsave, 0, -1);
@@ -563,6 +565,8 @@ int fpregs_set(struct task_struct *targe
sanitize_i387_state(target);
+ target->thread.fpu.last_cpu = ~0;
+
if (!HAVE_HWFP)
return fpregs_soft_set(target, regset, pos, count, kbuf, ubuf);
next reply other threads:[~2012-04-14 23:53 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-14 23:52 Oleg Nesterov [this message]
2012-04-14 23:59 ` ptrace && fpu_lazy_restore Oleg Nesterov
2012-04-15 2:03 ` Linus Torvalds
2012-04-15 22:38 ` Oleg Nesterov
2012-04-15 23:42 ` Linus Torvalds
2012-04-15 23:46 ` Linus Torvalds
2012-04-16 20:47 ` [PATCH 0/1] i387: ptrace breaks the lazy-fpu-restore logic Oleg Nesterov
2012-04-16 20:48 ` [PATCH 1/1] " Oleg Nesterov
2012-04-16 22:09 ` Oleg Nesterov
2012-04-17 0:05 ` [tip:x86/urgent] " tip-bot for Oleg Nesterov
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