linux-kernel - Re: [PATCH 4/5] x86-64: Replace vsyscall gettimeofday fallback with int 0xcc

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Date:	Sun, 29 May 2011 22:07:06 +0200 (CEST)
From:	Jesper Juhl <jj@...osbits.net>
To:	Andrew Lutomirski <luto@....edu>
cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] x86-64: Replace vsyscall gettimeofday fallback with
 int 0xcc

On Sun, 29 May 2011, Andrew Lutomirski wrote:

> On Sun, May 29, 2011 at 3:54 PM, Jesper Juhl <jj@...osbits.net> wrote:
> > On Sun, 29 May 2011, Jesper Juhl wrote:
> >
> >> On Fri, 27 May 2011, Andy Lutomirski wrote:
> >>
> >> > Now the only way to issue a syscall with side effects through the
> >> > vsyscall page is to call a misaligned instruction.  I haven't
> >> > checked for that.
> >> >
> >> > Signed-off-by: Andy Lutomirski <luto@....edu>
> >> > ---
> >> >  arch/x86/include/asm/traps.h    |    4 +++
> >> >  arch/x86/include/asm/vsyscall.h |    6 +++++
> >> >  arch/x86/kernel/entry_64.S      |    2 +
> >> >  arch/x86/kernel/traps.c         |    4 +++
> >> >  arch/x86/kernel/vsyscall_64.c   |   47 ++++++++++++++++++++++++++++++++++-----
> >> >  5 files changed, 57 insertions(+), 6 deletions(-)
> >> >
> >>
> >> one very tiny nit below.
> >>
> >> [...]
> >> > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> >> > index b9b6716..d34894e 100644
> >> > --- a/arch/x86/kernel/traps.c
> >> > +++ b/arch/x86/kernel/traps.c
> >> > @@ -872,6 +872,10 @@ void __init trap_init(void)
> >> >     set_bit(SYSCALL_VECTOR, used_vectors);
> >> >  #endif
> >> >
> >> > +   set_system_intr_gate(0xCC, &intcc);
> >> > +   set_bit(0xCC, used_vectors);
> >> > +   printk(KERN_ERR "intcc gate isntalled\n");
> >>
> >> Let's spell the error message correctly:
> >>
> >>       printk(KERN_ERR "intcc gate installed\n");
> >>
> > Hmm, why is this KERN_ERR btw? Shouldn't it just be KERN_NOTICE or
> > KERN_INFO ?
> 
> IMO it shouldn't be there at all.  It was a debugging leftover that I
> forgot to delete.
> 
Just removing it sounds good to me :)

-- 
Jesper Juhl <jj@...osbits.net>       http://www.chaosbits.net/
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