From: Ira Weiny <ira.weiny@intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Rik van Riel <riel@surriel.com>,
Dave Hansen <dave.hansen@intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>, <x86@kernel.org>,
<linux-kernel@vger.kernel.org>, <kernel-team@fb.com>
Subject: Re: [RFC PATCH 2/5] entry: Add calls for save/restore auxiliary pt_regs
Date: Tue, 9 Aug 2022 11:38:03 -0700 [thread overview]
Message-ID: <YvKpi/CVHko50PNQ@iweiny-desk3> (raw)
In-Reply-To: <YvJNe2rzXfcogFFX@zn.tnic>
On Tue, Aug 09, 2022 at 02:05:15PM +0200, Borislav Petkov wrote:
> On Fri, Aug 05, 2022 at 10:30:06AM -0700, ira.weiny@intel.com wrote:
> > From: Ira Weiny <ira.weiny@intel.com>
> >
> > Some architectures have auxiliary pt_regs space available to store
> > information on the stack during exceptions. This information is easier
> > to obtain and store within C code rather than in arch specific assembly.
>
> There are others?
Other archs? not now.
>
> Because I would've done this whole thing in arch/x86/ only...
Thomas did a lot of work to make the entry code generic. So I was keeping that
work consistent. This also helps to ensure I did not miss any places.
>
> > diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> > index 8c0f334c4b75..a70a0f314aee 100644
> > --- a/kernel/entry/common.c
> > +++ b/kernel/entry/common.c
> > @@ -317,7 +317,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
> >
> > if (user_mode(regs)) {
> > irqentry_enter_from_user_mode(regs);
> > - return ret;
> > + goto aux_save;
>
> Why do you have to goto and do the instrumentation sandwitch around it
> at the goto label?
>
> Why not simply do
>
> if (user_mode(regs)) {
> irqentry_enter_from_user_mode(regs);
> arch_save_aux_pt_regs(regs);
> return ret;
I don't believe this is correct because instrumentation is not enabled here.
See below.[1]
There are 3 exit paths from irqentry_enter(). All must call
arch_save_aux_pt_regs(). I felt the maintenance of the code would be easier if
I did not scatter those calls through the function and simply exited 1
place.[1]
FWICT calling instrumentation_{begin,end}() is a noop in production code. So
there is no real cost to calling instrumentation_begin() -> end -> begin ->
end. And the goto seemed low enough overhead. Given the current discussion I
admit I may have made the wrong choice. But I think I would add some comments
to the below to help future developers.
Ira
[1]
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -317,6 +317,9 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
if (user_mode(regs)) {
irqentry_enter_from_user_mode(regs);
+ instrumentation_begin();
+ arch_save_aux_pt_regs(regs);
+ instrumentation_end();
return ret;
}
@@ -353,6 +356,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
ct_irq_enter();
instrumentation_begin();
trace_hardirqs_off_finish();
+ arch_save_aux_pt_regs(regs);
instrumentation_end();
ret.exit_rcu = true;
@@ -369,6 +373,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
instrumentation_begin();
rcu_irq_enter_check_tick();
trace_hardirqs_off_finish();
+ arch_save_aux_pt_regs(regs);
instrumentation_end();
return ret;
next prev parent reply other threads:[~2022-08-09 19:04 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-05 17:30 [RFC PATCH 0/5] Print CPU at segfault time ira.weiny
2022-08-05 17:30 ` [RFC PATCH 1/5] entry: Pass pt_regs to irqentry_exit_cond_resched() ira.weiny
2022-08-05 18:33 ` Rik van Riel
2022-08-08 10:38 ` Borislav Petkov
2022-08-08 17:34 ` Ira Weiny
2022-08-08 17:38 ` Borislav Petkov
2022-08-08 17:43 ` Dave Hansen
2022-08-08 17:52 ` Borislav Petkov
2022-08-09 23:18 ` Thomas Gleixner
2022-08-10 7:25 ` Thomas Gleixner
2022-08-05 17:30 ` [RFC PATCH 2/5] entry: Add calls for save/restore auxiliary pt_regs ira.weiny
2022-08-05 18:34 ` Rik van Riel
2022-08-09 12:05 ` Borislav Petkov
2022-08-09 18:38 ` Ira Weiny [this message]
2022-08-09 18:49 ` Borislav Petkov
2022-08-09 21:14 ` Thomas Gleixner
2022-08-09 21:38 ` Borislav Petkov
2022-08-09 22:33 ` Ira Weiny
2022-08-09 21:49 ` Ira Weiny
2022-08-09 23:53 ` Thomas Gleixner
2022-08-05 17:30 ` [RFC PATCH 3/5] x86/entry: Add auxiliary pt_regs space ira.weiny
2022-08-05 18:45 ` Rik van Riel
2022-08-05 17:30 ` [RFC PATCH 4/5] x86,mm: print likely CPU at segfault time ira.weiny
2022-08-05 17:30 ` [RFC PATCH 5/5] x86/entry: Store CPU info on exception entry ira.weiny
2022-08-05 18:46 ` Rik van Riel
2022-08-05 18:47 ` Dave Hansen
2022-08-06 9:01 ` Ingo Molnar
2022-08-06 9:11 ` Borislav Petkov
2022-08-07 10:02 ` Ingo Molnar
2022-08-07 10:35 ` Borislav Petkov
2022-08-07 20:02 ` Ira Weiny
2022-08-08 11:03 ` Ingo Molnar
2022-08-08 12:01 ` Borislav Petkov
2022-08-09 20:06 ` Thomas Gleixner
2022-08-08 16:16 ` Dave Hansen
2022-08-08 17:24 ` Rik van Riel
2022-08-09 21:19 ` Andy Lutomirski
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