linux-kernel - [PATCH] x86, alternative: fix p6 nops on non-modular kernels

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Message-ID: <5034AE84.90708@redhat.com>
Date:	Wed, 22 Aug 2012 13:03:48 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Tomas Racek <tracek@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>
CC:	Michael Tokarev <mjt@....msk.ru>,
	Borislav Petkov <borislav.petkov@....com>,
	kvm-devel <kvm@...r.kernel.org>,
	Marcelo Tosatti <mtosatti@...hat.com>, qemu-devel@...gnu.org,
	linux-kernel@...r.kernel.org,
	Anthony Liguori <anthony@...emonkey.ws>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Alan Cox <alan@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86, alternative: fix p6 nops on non-modular kernels

On 08/22/2012 12:54 PM, Avi Kivity wrote:
> On 08/21/2012 12:28 PM, Tomas Racek wrote:
>> 
>> http://fi.muni.cz/~xracek/debian2.img.bz2
>> 
>> Other things are the same.
>> 
>> The runtest.sh sets environment for xfstests and runs test 285 which I wrote and and which should test if FS sends discard requests only on free sectors:
>> 285:
>> 1. Create loop device and FS on it.
>> 2. Populate it with some garbage.
>> 3. Get free sectors from FS.
>> 4. Run fstrim and look for discard requests via blk tracer.
>> 5. Compare free sectors to discard requests.
>> 
>> The test itself can have some issues but I'm pretty sure it shouldn't crash the system. ;-)
> 
> Does the following patch help?
> 

It's obvious that it should.  You're running a non-modular kernel, and those nops are discarded (probably a leftover from the days patching was a boot-only activity), so the kernel patched garbage over its own code.

-------8<----cut-here-----8<-----------------------------------

From: Avi Kivity <avi@...hat.com>
Date: Wed, 22 Aug 2012 12:58:18 +0300
Subject: [PATCH] x86, alternative: fix p6 nops on non-modular kernels

Probably a leftover from the early days of self-patching, p6nops are
marked __initconst_or_module, which causes them to be discarded in a
non-modular kernel.  If something later triggers patching, it will
overwrite kernel code with garbage.

Reported-by: Tomas Racek <tracek@...hat.com>
Signed-off-by: Avi Kivity <avi@...hat.com>

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index afb7ff7..ced4534 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -165,7 +165,7 @@ static int __init setup_noreplace_paravirt(char *str)
 #endif
 
 #ifdef P6_NOP1
-static const unsigned char  __initconst_or_module p6nops[] =
+static const unsigned char p6nops[] =
 {
 	P6_NOP1,
 	P6_NOP2,


-- 
error compiling committee.c: too many arguments to function
--
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