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

From: Tomas Racek <tracek@redhat.com>
To: Avi Kivity <avi@redhat.com>
Cc: Michael Tokarev <mjt@tls.msk.ru>,
	Borislav Petkov <borislav.petkov@amd.com>,
	kvm-devel <kvm@vger.kernel.org>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	qemu-devel@nongnu.org, linux-kernel@vger.kernel.org,
	Anthony Liguori <anthony@codemonkey.ws>,
	"H. Peter Anvin" <hpa@linux.intel.com>,
	Alan Cox <alan@lxorguk.ukuu.org.uk>,
	Alan Cox <alan@linux.intel.com>,
	the arch/x86 maintainers <x86@kernel.org>
Subject: Re: [PATCH] x86, alternative: fix p6 nops on non-modular kernels
Date: Wed, 22 Aug 2012 06:33:40 -0400 (EDT)	[thread overview]
Message-ID: <1406258973.2560632.1345631620655.JavaMail.root@redhat.com> (raw)
In-Reply-To: <5034AE84.90708@redhat.com>

----- Original Message -----
> 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.
> 

Works fine. Thank you!

Tom

> -------8<----cut-here-----8<-----------------------------------
> 
> From: Avi Kivity <avi@redhat.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@redhat.com>
> Signed-off-by: Avi Kivity <avi@redhat.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
> 