linux-kernel - Re: [PATCH] s390, sched: Fix thread_struct move fallout to __switch

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Date:	Mon, 20 Jul 2015 10:34:47 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...nel.org>, Dave Hansen <dave@...1.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] s390, sched: Fix thread_struct move fallout to
 __switch_to()


* Ingo Molnar <mingo@...nel.org> wrote:

> I also looked at fixing pgm_check_handler(), but my s390-fu gave up completely 
> on that one: task_struct is in 'r14', but this is a hardware entry function it 
> appears. So to fix it we'd have to pick a temporary register, put thread_struct 
> pointer into it, and fix up these offsets:
> 
> arch/s390/kernel/asm-offsets.c: DEFINE(__THREAD_per_address, offsetof(struct task_struct, thread.per_event.address));
> arch/s390/kernel/asm-offsets.c: DEFINE(__THREAD_per_paid, offsetof(struct task_struct, thread.per_event.paid));
> arch/s390/kernel/asm-offsets.c: DEFINE(__THREAD_trap_tdb, offsetof(struct task_struct, thread.trap_tdb));
> 
> to be thread_struct relative.

Here's a stab at that: we can move 'r14' from 'current' to 'current->thread' and 
back relatively cheaply I think. If I got the mnemonics right.

Thanks,

	Ingo

===============================>

 arch/s390/kernel/asm-offsets.c | 9 +++++----
 arch/s390/kernel/entry.S       | 2 ++
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c
index 2b422297660f..26edbc4b5078 100644
--- a/arch/s390/kernel/asm-offsets.c
+++ b/arch/s390/kernel/asm-offsets.c
@@ -24,13 +24,14 @@
 int main(void)
 {
 	DEFINE(__TASK_thread_info, offsetof(struct task_struct, stack));
+	DEFINE(__TASK_thread_struct, offsetof(struct task_struct, thread));
 	DEFINE(__THREAD_ksp, offsetof(struct thread_struct, ksp));
 	BLANK();
 	DEFINE(__TASK_pid, offsetof(struct task_struct, pid));
 	BLANK();
-	DEFINE(__THREAD_per_cause, offsetof(struct task_struct, thread.per_event.cause));
-	DEFINE(__THREAD_per_address, offsetof(struct task_struct, thread.per_event.address));
-	DEFINE(__THREAD_per_paid, offsetof(struct task_struct, thread.per_event.paid));
+	DEFINE(__THREAD_per_cause, offsetof(struct thread_struct, per_event.cause));
+	DEFINE(__THREAD_per_address, offsetof(struct thread_struct, per_event.address));
+	DEFINE(__THREAD_per_paid, offsetof(struct thread_struct, per_event.paid));
 	BLANK();
 	DEFINE(__TI_task, offsetof(struct thread_info, task));
 	DEFINE(__TI_flags, offsetof(struct thread_info, flags));
@@ -175,7 +176,7 @@ int main(void)
 	DEFINE(__LC_VDSO_PER_CPU, offsetof(struct _lowcore, vdso_per_cpu_data));
 	DEFINE(__LC_GMAP, offsetof(struct _lowcore, gmap));
 	DEFINE(__LC_PGM_TDB, offsetof(struct _lowcore, pgm_tdb));
-	DEFINE(__THREAD_trap_tdb, offsetof(struct task_struct, thread.trap_tdb));
+	DEFINE(__THREAD_trap_tdb, offsetof(struct thread_struct, trap_tdb));
 	DEFINE(__GMAP_ASCE, offsetof(struct gmap, asce));
 	DEFINE(__SIE_PROG0C, offsetof(struct kvm_s390_sie_block, prog0c));
 	DEFINE(__SIE_PROG20, offsetof(struct kvm_s390_sie_block, prog20));
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index c2fcb9e7ad25..9806b2f94985 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -421,6 +421,7 @@ ENTRY(pgm_check_handler)
 	LAST_BREAK %r14
 	lg	%r15,__LC_KERNEL_STACK
 	lg	%r14,__TI_task(%r12)
+	ahi     %r14,__TASK_thread_struct # r14 now points to 'current->thread'
 	lghi	%r13,__LC_PGM_TDB
 	tm	__LC_PGM_ILC+2,0x02	# check for transaction abort
 	jz	2f
@@ -448,6 +449,7 @@ ENTRY(pgm_check_handler)
 	nill	%r10,0x007f
 	sll	%r10,2
 	je	.Lsysc_return
+	ahi     %r14,-__TASK_thread_struct # r14 now points to 'current'
 	lgf	%r1,0(%r10,%r1)		# load address of handler routine
 	lgr	%r2,%r11		# pass pointer to pt_regs
 	basr	%r14,%r1		# branch to interrupt-handler

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