From: Andy Lutomirski <luto@amacapital.net>
To: Borislav Petkov <bp@alien8.de>
Cc: "X86 ML" <x86@kernel.org>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Peter Zijlstra" <peterz@infradead.org>,
"Oleg Nesterov" <oleg@redhat.com>,
"Tony Luck" <tony.luck@intel.com>,
"Andi Kleen" <andi@firstfloor.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
"Josh Triplett" <josh@joshtriplett.org>,
"Frédéric Weisbecker" <fweisbec@gmail.com>
Subject: Re: [PATCH v4 2/5] x86, traps: Track entry into and exit from IST context
Date: Mon, 24 Nov 2014 11:48:43 -0800 [thread overview]
Message-ID: <CALCETrWwPz=GNwo=tNyc2_2xsQxtd1qcLj5Sw-Qw2Ox_U93jSQ@mail.gmail.com> (raw)
In-Reply-To: <20141122172025.GC4395@pd.tnic>
On Sat, Nov 22, 2014 at 9:20 AM, Borislav Petkov <bp@alien8.de> wrote:
> On Fri, Nov 21, 2014 at 01:26:08PM -0800, Andy Lutomirski wrote:
>> We currently pretend that IST context is like standard exception
>> context, but this is incorrect. IST entries from userspace are like
>> standard exceptions except that they use per-cpu stacks, so they are
>> atomic. IST entries from kernel space are like NMIs from RCU's
>> perspective -- they are not quiescent states even if they
>> interrupted the kernel during a quiescent state.
>>
>> Add and use ist_enter and ist_exit to track IST context. Even
>> though x86_32 has no IST stacks, we track these interrupts the same
>> way.
>>
>> This fixes two issues:
>>
>> - Scheduling from an IST interrupt handler will now warn. It would
>> previously appear to work as long as we got lucky and nothing
>> overwrote the stack frame. (I don't know of any bugs in this
>> that would trigger the warning, but it's good to be on the safe
>> side.)
>>
>> - RCU handling in IST context was dangerous. As far as I know,
>> only machine checks were likely to trigger this, but it's good to
>> be on the safe side.
>>
>> Note that the machine check handlers appears to have been missing
>> any context tracking at all before this patch.
>>
>> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
>> Cc: Josh Triplett <josh@joshtriplett.org>
>> Cc: Frédéric Weisbecker <fweisbec@gmail.com>
>> Signed-off-by: Andy Lutomirski <luto@amacapital.net>
>> ---
>> arch/x86/include/asm/traps.h | 4 +++
>> arch/x86/kernel/cpu/mcheck/mce.c | 5 ++++
>> arch/x86/kernel/cpu/mcheck/p5.c | 6 +++++
>> arch/x86/kernel/cpu/mcheck/winchip.c | 5 ++++
>> arch/x86/kernel/traps.c | 49 ++++++++++++++++++++++++++++++------
>> 5 files changed, 61 insertions(+), 8 deletions(-)
>
> ...
>
>> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
>> index 0d0e922fafc1..f5c4b8813774 100644
>> --- a/arch/x86/kernel/traps.c
>> +++ b/arch/x86/kernel/traps.c
>> @@ -107,6 +107,39 @@ static inline void preempt_conditional_cli(struct pt_regs *regs)
>> preempt_count_dec();
>> }
>>
>> +enum ctx_state ist_enter(struct pt_regs *regs)
>> +{
>> + /*
>> + * We are atomic because we're on the IST stack (or we're on x86_32,
>> + * in which case we still shouldn't schedule.
>> + */
>> + preempt_count_add(HARDIRQ_OFFSET);
>> +
>> + if (user_mode_vm(regs)) {
>> + /* Other than that, we're just an exception. */
>> + return exception_enter();
>> + } else {
>> + /*
>> + * We might have interrupted pretty much anything. In
>> + * fact, if we're a machine check, we can even interrupt
>> + * NMI processing. We don't want in_nmi() to return true,
>> + * but we need to notify RCU.
>> + */
>> + rcu_nmi_enter();
>> + return IN_KERNEL; /* the value is irrelevant. */
>> + }
>
> I guess dropping the explicit else-branch could make it look a bit nicer
> with the curly braces gone and all...
>
> enum ctx_state ist_enter(struct pt_regs *regs)
> {
> /*
> * We are atomic because we're on the IST stack (or we're on x86_32,
> * in which case we still shouldn't schedule.
> */
> preempt_count_add(HARDIRQ_OFFSET);
>
> if (user_mode_vm(regs))
> /* Other than that, we're just an exception. */
> return exception_enter();
>
Two indented lines w/o curly braces makes me think of goto fail; :-/
TBH, when there are clearly two options, I tend to prefer the braces
that make it very obvious what's going on. I had some memorable bugs
several years ago that would have been impossible if I has used braces
more liberally.
--Andy
> /*
> * We might have interrupted pretty much anything. In fact, if we're a
> * machine check, we can even interrupt NMI processing. We don't want
> * in_nmi() to return true, but we need to notify RCU.
> */
> rcu_nmi_enter();
> return IN_KERNEL; /* the value is irrelevant. */
> }
>
>> +}
>> +
>> +void ist_exit(struct pt_regs *regs, enum ctx_state prev_state)
>> +{
>> + preempt_count_sub(HARDIRQ_OFFSET);
>> +
>> + if (user_mode_vm(regs))
>> + return exception_exit(prev_state);
>> + else
>> + rcu_nmi_exit();
>> +}
>
> Ditto here.
>
>> +
>> static nokprobe_inline int
>> do_trap_no_signal(struct task_struct *tsk, int trapnr, char *str,
>> struct pt_regs *regs, long error_code)
>
> --
> Regards/Gruss,
> Boris.
>
> Sent from a fat crate under my desk. Formatting is fine.
> --
--
Andy Lutomirski
AMA Capital Management, LLC
next prev parent reply other threads:[~2014-11-24 19:49 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-21 21:26 [PATCH v4 0/5] x86: Rework IST interrupts Andy Lutomirski
2014-11-21 21:26 ` [PATCH v4 1/5] uprobes, x86: Fix _TIF_UPROBE vs _TIF_NOTIFY_RESUME Andy Lutomirski
2014-11-22 16:55 ` Borislav Petkov
2014-11-24 17:58 ` Andy Lutomirski
2014-11-21 21:26 ` [PATCH v4 2/5] x86, traps: Track entry into and exit from IST context Andy Lutomirski
2014-11-21 21:32 ` Andy Lutomirski
2014-11-21 22:07 ` Paul E. McKenney
2014-11-21 22:19 ` Andy Lutomirski
2014-11-21 22:55 ` Paul E. McKenney
2014-11-21 23:06 ` Andy Lutomirski
2014-11-21 23:38 ` Paul E. McKenney
2014-11-22 2:00 ` Andy Lutomirski
2014-11-22 4:20 ` Paul E. McKenney
2014-11-22 5:53 ` Andy Lutomirski
2014-11-22 23:41 ` Paul E. McKenney
2014-11-24 20:22 ` Andy Lutomirski
2014-11-24 20:54 ` Paul E. McKenney
2014-11-24 21:02 ` Andy Lutomirski
2014-11-24 21:35 ` Paul E. McKenney
2014-11-24 22:34 ` Paul E. McKenney
2014-11-24 22:36 ` Andy Lutomirski
2014-11-24 22:57 ` Paul E. McKenney
2014-11-24 23:31 ` Paul E. McKenney
2014-11-24 23:35 ` Andy Lutomirski
2014-11-24 23:50 ` Paul E. McKenney
2014-11-24 23:52 ` Andy Lutomirski
2014-11-25 18:58 ` Borislav Petkov
2014-11-25 19:16 ` Paul E. McKenney
2014-12-11 0:22 ` Tony Luck
2014-12-11 0:24 ` Andy Lutomirski
2015-01-05 21:46 ` Tony Luck
2015-01-05 21:54 ` Andy Lutomirski
2015-01-06 0:44 ` [PATCH] x86, mce: Get rid of TIF_MCE_NOTIFY and associated mce tricks Luck, Tony
2015-01-06 1:01 ` Andy Lutomirski
2015-01-06 18:00 ` Luck, Tony
2015-01-07 12:13 ` Borislav Petkov
2015-01-07 15:51 ` Andy Lutomirski
2015-01-07 15:58 ` Borislav Petkov
2015-01-07 16:12 ` Paul E. McKenney
2014-11-25 17:13 ` [PATCH v4 2/5] x86, traps: Track entry into and exit from IST context Paul E. McKenney
2014-11-27 7:03 ` Lai Jiangshan
2014-11-27 16:46 ` Paul E. McKenney
2014-11-24 21:27 ` Paul E. McKenney
2014-11-21 22:20 ` Frederic Weisbecker
2014-11-21 22:00 ` Paul E. McKenney
2014-11-22 17:20 ` Borislav Petkov
2014-11-24 19:48 ` Andy Lutomirski [this message]
2015-01-22 21:52 ` Sasha Levin
2015-01-23 17:58 ` Andy Lutomirski
2015-01-23 18:04 ` Borislav Petkov
2015-01-23 18:34 ` Andy Lutomirski
2015-01-23 20:48 ` Sasha Levin
2015-01-24 1:25 ` Andy Lutomirski
2015-01-28 16:33 ` Andy Lutomirski
2015-01-28 17:48 ` Paul E. McKenney
2015-01-28 21:02 ` Andy Lutomirski
2015-01-30 19:57 ` Sasha Levin
2015-01-31 1:28 ` Sasha Levin
2015-01-31 3:12 ` Andy Lutomirski
2015-01-31 12:50 ` Andy Lutomirski
2015-01-31 13:01 ` [PATCH] x86, traps: Fix ist_enter from userspace Andy Lutomirski
2015-01-31 15:09 ` Sasha Levin
2015-01-31 16:18 ` Paul E. McKenney
2015-02-01 2:17 ` Andy Lutomirski
2015-02-04 6:01 ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2014-11-21 21:26 ` [PATCH v4 3/5] x86, entry: Switch stacks on a paranoid entry " Andy Lutomirski
2014-11-24 15:55 ` Borislav Petkov
2014-11-21 21:26 ` [PATCH v4 4/5] x86: Clean up current_stack_pointer Andy Lutomirski
2014-11-24 11:39 ` Borislav Petkov
2014-11-21 21:26 ` [PATCH v4 5/5] x86, traps: Add ist_begin_non_atomic and ist_end_non_atomic Andy Lutomirski
2014-11-24 15:54 ` Borislav Petkov
2014-11-24 19:52 ` Andy Lutomirski
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CALCETrWwPz=GNwo=tNyc2_2xsQxtd1qcLj5Sw-Qw2Ox_U93jSQ@mail.gmail.com' \
--to=luto@amacapital.net \
--cc=andi@firstfloor.org \
--cc=bp@alien8.de \
--cc=fweisbec@gmail.com \
--cc=josh@joshtriplett.org \
--cc=linux-kernel@vger.kernel.org \
--cc=oleg@redhat.com \
--cc=paulmck@linux.vnet.ibm.com \
--cc=peterz@infradead.org \
--cc=tony.luck@intel.com \
--cc=torvalds@linux-foundation.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).