linux-kernel - Re: [RFC PATCH v2 10/18] livepatch/powerpc: add TIF_PATCH

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Date:	Tue, 3 May 2016 14:06:42 +0200 (CEST)
From:	Miroslav Benes <mbenes@...e.cz>
To:	Petr Mladek <pmladek@...e.com>
cc:	Josh Poimboeuf <jpoimboe@...hat.com>, Jessica Yu <jeyu@...hat.com>,
	Jiri Kosina <jikos@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-s390@...r.kernel.org, Vojtech Pavlik <vojtech@...e.com>,
	Jiri Slaby <jslaby@...e.cz>,
	Chris J Arges <chris.j.arges@...onical.com>,
	Andy Lutomirski <luto@...nel.org>
Subject: Re: [RFC PATCH v2 10/18] livepatch/powerpc: add TIF_PATCH_PENDING
 thread flag

On Tue, 3 May 2016, Petr Mladek wrote:

> On Thu 2016-04-28 15:44:41, Josh Poimboeuf wrote:
> > Add the TIF_PATCH_PENDING thread flag to enable the new livepatch
> > per-task consistency model for powerpc.  The bit getting set indicates
> > the thread has a pending patch which needs to be applied when the thread
> > exits the kernel.
> > 
> > The bit is included in the _TIF_USER_WORK_MASK macro so that
> > do_notify_resume() and klp_patch_task() get called when the bit is set.
> > 
> > Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> > ---
> >  arch/powerpc/include/asm/thread_info.h | 4 +++-
> >  arch/powerpc/kernel/signal.c           | 4 ++++
> >  2 files changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
> > index 8febc3f..df262ca 100644
> > --- a/arch/powerpc/include/asm/thread_info.h
> > +++ b/arch/powerpc/include/asm/thread_info.h
> > @@ -88,6 +88,7 @@ static inline struct thread_info *current_thread_info(void)
> >  					   TIF_NEED_RESCHED */
> >  #define TIF_32BIT		4	/* 32 bit binary */
> >  #define TIF_RESTORE_TM		5	/* need to restore TM FP/VEC/VSX */
> > +#define TIF_PATCH_PENDING	6	/* pending live patching update */
> >  #define TIF_SYSCALL_AUDIT	7	/* syscall auditing active */
> >  #define TIF_SINGLESTEP		8	/* singlestepping active */
> >  #define TIF_NOHZ		9	/* in adaptive nohz mode */
> > @@ -111,6 +112,7 @@ static inline struct thread_info *current_thread_info(void)
> >  #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
> >  #define _TIF_32BIT		(1<<TIF_32BIT)
> >  #define _TIF_RESTORE_TM		(1<<TIF_RESTORE_TM)
> > +#define _TIF_PATCH_PENDING	(1<<TIF_PATCH_PENDING)
> >  #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
> >  #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
> >  #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
> > @@ -127,7 +129,7 @@ static inline struct thread_info *current_thread_info(void)
> >  
> >  #define _TIF_USER_WORK_MASK	(_TIF_SIGPENDING | _TIF_NEED_RESCHED | \
> >  				 _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
> > -				 _TIF_RESTORE_TM)
> > +				 _TIF_RESTORE_TM | _TIF_PATCH_PENDING)
> >  #define _TIF_PERSYSCALL_MASK	(_TIF_RESTOREALL|_TIF_NOERROR)
> >  
> >  /* Bits in local_flags */
> > diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
> > index cb64d6f..844497b 100644
> > --- a/arch/powerpc/kernel/signal.c
> > +++ b/arch/powerpc/kernel/signal.c
> > @@ -14,6 +14,7 @@
> >  #include <linux/uprobes.h>
> >  #include <linux/key.h>
> >  #include <linux/context_tracking.h>
> > +#include <linux/livepatch.h>
> >  #include <asm/hw_breakpoint.h>
> >  #include <asm/uaccess.h>
> >  #include <asm/unistd.h>
> > @@ -159,6 +160,9 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags)
> >  		tracehook_notify_resume(regs);
> >  	}
> >  
> > +	if (thread_info_flags & _TIF_PATCH_PENDING)
> > +		klp_patch_task(current);
> > +
> 
> JFYI, if we later add the fake signal to speed up migration of
> sleeping task, we would need to move this up before calling
> do_signal(). It would help to avoid cycling here twice.
> Mirek surely knows more details about it.

Yes, that is true if we go with a fake signal implementation we have in 
kGraft. Nevertheless it is the issue of that patch so let's discuss that 
there (when I send it).

Miroslav