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From: Marcelo Tosatti <mtosatti@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>,
	Nicolas Saenz Julienne <nsaenzju@redhat.com>
Cc: gor@linux.ibm.com, jpoimboe@redhat.com, jikos@kernel.org,
	mbenes@suse.cz, pmladek@suse.com, mingo@kernel.org,
	linux-kernel@vger.kernel.org, joe.lawrence@redhat.com,
	fweisbec@gmail.com, tglx@linutronix.de, hca@linux.ibm.com,
	svens@linux.ibm.com, sumanthk@linux.ibm.com,
	live-patching@vger.kernel.org, paulmck@kernel.org,
	rostedt@goodmis.org, x86@kernel.org
Subject: Re: [RFC][PATCH v2 11/11] context_tracking,x86: Fix text_poke_sync() vs NOHZ_FULL
Date: Thu, 21 Oct 2021 15:40:42 -0300	[thread overview]
Message-ID: <20211021184042.GA19307@fuller.cnet> (raw)
In-Reply-To: <20211021183935.GA9071@fuller.cnet>

+CC Nicolas.

On Thu, Oct 21, 2021 at 03:39:35PM -0300, Marcelo Tosatti wrote:
> Peter,
> 
> static __always_inline void arch_exit_to_user_mode(void)
> {
>         mds_user_clear_cpu_buffers();
> }
> 
> /**
>  * mds_user_clear_cpu_buffers - Mitigation for MDS and TAA vulnerability
>  *
>  * Clear CPU buffers if the corresponding static key is enabled
>  */
> static __always_inline void mds_user_clear_cpu_buffers(void)
> {
>         if (static_branch_likely(&mds_user_clear))
>                 mds_clear_cpu_buffers();
> }
> 
> We were discussing how to perform objtool style validation 
> that no code after the check for 
> 
> > +             /* NMI happens here and must still do/finish CT_WORK_n */
> > +             sync_core();
> 
> But after the discussion with you, it seems doing the TLB checking 
> and (also sync_core) checking very late/very early on exit/entry 
> makes things easier to review.
> 
> Can then use a single atomic variable with USER/KERNEL state and cmpxchg
> loops.
> 
> On Wed, Sep 29, 2021 at 05:17:34PM +0200, Peter Zijlstra wrote:
> > Use the new context_tracking infrastructure to avoid disturbing
> > userspace tasks when we rewrite kernel code.
> > 
> > XXX re-audit the entry code to make sure only the context_tracking
> > static_branch is before hitting this code.
> > 
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---
> >  arch/x86/include/asm/sync_core.h |    2 ++
> >  arch/x86/kernel/alternative.c    |    8 +++++++-
> >  include/linux/context_tracking.h |    1 +
> >  kernel/context_tracking.c        |   12 ++++++++++++
> >  4 files changed, 22 insertions(+), 1 deletion(-)
> > 
> > --- a/arch/x86/include/asm/sync_core.h
> > +++ b/arch/x86/include/asm/sync_core.h
> > @@ -87,6 +87,8 @@ static inline void sync_core(void)
> >  	 */
> >  	iret_to_self();
> >  }
> > +#define sync_core sync_core
> > +
> >  
> >  /*
> >   * Ensure that a core serializing instruction is issued before returning
> > --- a/arch/x86/kernel/alternative.c
> > +++ b/arch/x86/kernel/alternative.c
> > @@ -18,6 +18,7 @@
> >  #include <linux/mmu_context.h>
> >  #include <linux/bsearch.h>
> >  #include <linux/sync_core.h>
> > +#include <linux/context_tracking.h>
> >  #include <asm/text-patching.h>
> >  #include <asm/alternative.h>
> >  #include <asm/sections.h>
> > @@ -924,9 +925,14 @@ static void do_sync_core(void *info)
> >  	sync_core();
> >  }
> >  
> > +static bool do_sync_core_cond(int cpu, void *info)
> > +{
> > +	return !context_tracking_set_cpu_work(cpu, CT_WORK_SYNC);
> > +}
> > +
> >  void text_poke_sync(void)
> >  {
> > -	on_each_cpu(do_sync_core, NULL, 1);
> > +	on_each_cpu_cond(do_sync_core_cond, do_sync_core, NULL, 1);
> >  }
> >  
> >  struct text_poke_loc {
> > --- a/include/linux/context_tracking.h
> > +++ b/include/linux/context_tracking.h
> > @@ -11,6 +11,7 @@
> >  
> >  enum ct_work {
> >  	CT_WORK_KLP = 1,
> > +	CT_WORK_SYNC = 2,
> >  };
> >  
> >  /*
> > --- a/kernel/context_tracking.c
> > +++ b/kernel/context_tracking.c
> > @@ -51,6 +51,10 @@ static __always_inline void context_trac
> >  	__this_cpu_dec(context_tracking.recursion);
> >  }
> >  
> > +#ifndef sync_core
> > +static inline void sync_core(void) { }
> > +#endif
> > +
> >  /* CT_WORK_n, must be noinstr, non-blocking, NMI safe and deal with spurious calls */
> >  static noinstr void ct_exit_user_work(struct context_tracking *ct)
> >  {
> > @@ -64,6 +68,14 @@ static noinstr void ct_exit_user_work(struct
> >  		arch_atomic_andnot(CT_WORK_KLP, &ct->work);
> >  	}
> >  
> > +	if (work & CT_WORK_SYNC) {
> > +		/* NMI happens here and must still do/finish CT_WORK_n */
> > +		sync_core();
> > +
> > +		smp_mb__before_atomic();
> > +		arch_atomic_andnot(CT_WORK_SYNC, &ct->work);
> > +	}
> > +
> >  	smp_mb__before_atomic();
> >  	arch_atomic_andnot(CT_SEQ_WORK, &ct->seq);
> >  }
> > 
> > 
> > 


  reply	other threads:[~2021-10-21 18:41 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-29 15:17 [PATCH v2 00/11] sched,rcu,context_tracking,livepatch: Improve livepatch task transitions for idle and NOHZ_FULL Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 01/11] sched: Improve try_invoke_on_locked_down_task() Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 02/11] sched,rcu: Rework try_invoke_on_locked_down_task() Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 03/11] sched,livepatch: Use task_call_func() Peter Zijlstra
2021-10-05 11:40   ` Petr Mladek
2021-10-05 14:03     ` Peter Zijlstra
2021-10-06  8:59   ` Miroslav Benes
2021-09-29 15:17 ` [PATCH v2 04/11] sched: Simplify wake_up_*idle*() Peter Zijlstra
2021-10-13 14:32   ` Qian Cai
2021-10-19  3:47     ` Qian Cai
2021-10-19  8:56       ` Peter Zijlstra
2021-10-19  9:10         ` Peter Zijlstra
2021-10-19 15:32           ` Qian Cai
2021-10-19 15:50             ` Peter Zijlstra
2021-10-19 19:22               ` Qian Cai
2021-10-19 20:27                 ` Peter Zijlstra
     [not found]   ` <CGME20211022134630eucas1p2e79e2816587d182c580459d567c1f2a9@eucas1p2.samsung.com>
2021-10-22 13:46     ` Marek Szyprowski
2021-09-29 15:17 ` [PATCH v2 05/11] sched,livepatch: Use wake_up_if_idle() Peter Zijlstra
2021-10-05 12:00   ` Petr Mladek
2021-10-06  9:16   ` Miroslav Benes
2021-10-07  9:18     ` Vasily Gorbik
2021-10-07 10:02       ` Peter Zijlstra
2021-10-13 19:37   ` Arnd Bergmann
2021-10-14 10:42     ` Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 06/11] context_tracking: Prefix user_{enter,exit}*() Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 07/11] context_tracking: Add an atomic sequence/state count Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 08/11] context_tracking,rcu: Replace RCU dynticks counter with context_tracking Peter Zijlstra
2021-09-29 18:37   ` Paul E. McKenney
2021-09-29 19:09     ` Peter Zijlstra
2021-09-29 19:11     ` Peter Zijlstra
2021-09-29 19:13     ` Peter Zijlstra
2021-09-29 19:24       ` Peter Zijlstra
2021-09-29 19:45         ` Paul E. McKenney
2021-09-29 18:54   ` Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 09/11] context_tracking,livepatch: Dont disturb NOHZ_FULL Peter Zijlstra
2021-10-06  8:12   ` Petr Mladek
2021-10-06  9:04     ` Peter Zijlstra
2021-10-06 10:29       ` Petr Mladek
2021-10-06 11:41         ` Peter Zijlstra
2021-10-06 11:48         ` Miroslav Benes
2021-09-29 15:17 ` [RFC][PATCH v2 10/11] livepatch: Remove klp_synchronize_transition() Peter Zijlstra
2021-10-06 12:30   ` Petr Mladek
2021-09-29 15:17 ` [RFC][PATCH v2 11/11] context_tracking,x86: Fix text_poke_sync() vs NOHZ_FULL Peter Zijlstra
2021-10-21 18:39   ` Marcelo Tosatti
2021-10-21 18:40     ` Marcelo Tosatti [this message]
2021-10-21 19:25     ` Peter Zijlstra
2021-10-21 19:57       ` Marcelo Tosatti
2021-10-21 20:18         ` Peter Zijlstra
2021-10-26 18:19           ` Marcelo Tosatti
2021-10-26 19:38             ` Peter Zijlstra
2021-09-29 18:03 ` [PATCH v2 00/11] sched,rcu,context_tracking,livepatch: Improve livepatch task transitions for idle and NOHZ_FULL Paul E. McKenney

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