linux-kernel - [tip:tracing/core] x86: implement atomic text

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Date:	Sun, 8 Mar 2009 15:51:50 GMT
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, mathieu.desnoyers@...ymtl.ca,
	hpa@...or.com, mingo@...hat.com, tglx@...utronix.de,
	mhiramat@...hat.com, mingo@...e.hu
Subject: [tip:tracing/core] x86: implement atomic text_poke() via fixmap

Commit-ID:  78ff7fae04554b49d29226ed12536268c2500d1f
Gitweb:     http://git.kernel.org/tip/78ff7fae04554b49d29226ed12536268c2500d1f
Author:     "Masami Hiramatsu" <mhiramat@...hat.com>
AuthorDate: Fri, 6 Mar 2009 10:37:54 -0500
Commit:     Ingo Molnar <mingo@...e.hu>
CommitDate: Fri, 6 Mar 2009 16:49:01 +0100

x86: implement atomic text_poke() via fixmap

Use fixmaps instead of vmap/vunmap in text_poke() for avoiding
page allocation and delayed unmapping.

At the result of above change, text_poke() becomes atomic and can be called
from stop_machine() etc.

Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
LKML-Reference: <49B14352.2040705@...hat.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>


---
 arch/x86/include/asm/fixmap.h |    2 ++
 arch/x86/kernel/alternative.c |   24 +++++++++++++++---------
 2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
index 63a79c7..81937a5 100644
--- a/arch/x86/include/asm/fixmap.h
+++ b/arch/x86/include/asm/fixmap.h
@@ -111,6 +111,8 @@ enum fixed_addresses {
 #ifdef CONFIG_PARAVIRT
 	FIX_PARAVIRT_BOOTMAP,
 #endif
+	FIX_TEXT_POKE0,	/* reserve 2 pages for text_poke() */
+	FIX_TEXT_POKE1,
 	__end_of_permanent_fixed_addresses,
 #ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT
 	FIX_OHCI1394_BASE,
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 092a7b8..2d903b7 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -13,7 +13,9 @@
 #include <asm/nmi.h>
 #include <asm/vsyscall.h>
 #include <asm/cacheflush.h>
+#include <asm/tlbflush.h>
 #include <asm/io.h>
+#include <asm/fixmap.h>
 
 #define MAX_PATCH_LEN (255-1)
 
@@ -505,15 +507,16 @@ void *text_poke_early(void *addr, const void *opcode, size_t len)
  * It means the size must be writable atomically and the address must be aligned
  * in a way that permits an atomic write. It also makes sure we fit on a single
  * page.
+ *
+ * Note: Must be called under text_mutex.
  */
 void *__kprobes text_poke(void *addr, const void *opcode, size_t len)
 {
+	unsigned long flags;
 	char *vaddr;
-	int nr_pages = 2;
 	struct page *pages[2];
 	int i;
 
-	might_sleep();
 	if (!core_kernel_text((unsigned long)addr)) {
 		pages[0] = vmalloc_to_page(addr);
 		pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
@@ -523,14 +526,17 @@ void *__kprobes text_poke(void *addr, const void *opcode, size_t len)
 		pages[1] = virt_to_page(addr + PAGE_SIZE);
 	}
 	BUG_ON(!pages[0]);
-	if (!pages[1])
-		nr_pages = 1;
-	vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
-	BUG_ON(!vaddr);
-	local_irq_disable();
+	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_enable();
-	vunmap(vaddr);
+	local_irq_restore(flags);
+	clear_fixmap(FIX_TEXT_POKE0);
+	if (pages[1])
+		clear_fixmap(FIX_TEXT_POKE1);
+	local_flush_tlb();
 	sync_core();
 	/* Could also do a CLFLUSH here to speed up CPU recovery; but
 	   that causes hangs on some VIA CPUs. */
--
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