linux-kernel - Re: [PATCH -tip 5/4] Expands irq-off region in text

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Date:	Mon, 09 Mar 2009 12:40:40 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH -tip 5/4] Expands irq-off region in text_poke()

Mathieu Desnoyers wrote:
>>> I think irq off should cover the BUG_ON too. This safety check assumes
>>> we are the only ones modifying "addr".
>> I think others don't change without text_mutex, don't it?
>>
> 
> They shouldn't, but given we decided to grow the irq off region to
> contain all the code that needs to be executed atomically, it should
> also contain the BUG_ON, because it is expected to be as atomic as the
> rest of the code.

Hm, sure, I updated the delta patch.

Expand irq-off region to cover fixmap using code and cache synchronizing.

Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc: Ingo Molnar <mingo@...e.hu>
---
 arch/x86/kernel/alternative.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: linux-2.6-tip/arch/x86/kernel/alternative.c
===================================================================
--- linux-2.6-tip.orig/arch/x86/kernel/alternative.c
+++ linux-2.6-tip/arch/x86/kernel/alternative.c
@@ -526,13 +526,12 @@ void *__kprobes text_poke(void *addr, co
 		pages[1] = virt_to_page(addr + PAGE_SIZE);
 	}
 	BUG_ON(!pages[0]);
+	local_irq_save(flags);
 	set_fixmap(FIX_TEXT_POKE0, page_to_phys(pages[0]));
 	if (pages[1])
 		set_fixmap(FIX_TEXT_POKE1, page_to_phys(pages[1]));
 	vaddr = (char *)fix_to_virt(FIX_TEXT_POKE0);
-	local_irq_save(flags);
 	memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
-	local_irq_restore(flags);
 	clear_fixmap(FIX_TEXT_POKE0);
 	if (pages[1])
 		clear_fixmap(FIX_TEXT_POKE1);
@@ -542,5 +541,6 @@ void *__kprobes text_poke(void *addr, co
 	   that causes hangs on some VIA CPUs. */
 	for (i = 0; i < len; i++)
 		BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]);
+	local_irq_restore(flags);
 	return addr;
 }

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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