linux-kernel - Re: [PATCH v2] x86/entry/32: Remove duplicate initialization of tss.ss1

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Message-ID: <20150824064822.GB12756@gmail.com>
Date:	Mon, 24 Aug 2015 08:48:22 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Brian Gerst <brgerst@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>, Willy Tarreau <w@....eu>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2] x86/entry/32: Remove duplicate initialization of
 tss.ss1


* Andy Lutomirski <luto@...capital.net> wrote:

> On Sun, Aug 23, 2015 at 4:26 AM, Ingo Molnar <mingo@...nel.org> wrote:
> >
> > * Andy Lutomirski <luto@...nel.org> wrote:
> >
> >> It's statically initialized, so we don't need to dynamically
> >> initialize it too.
> >>
> >> Reported-by: Brian Gerst <brgerst@...il.com>
> >> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> >> ---
> >>
> >> Changes since v1: Delete the code :)
> >>
> >> arch/x86/kernel/cpu/common.c | 8 --------
> >>  1 file changed, 8 deletions(-)
> >>
> >> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> >> index e2ed2513a51e..e08eee98a5f8 100644
> >> --- a/arch/x86/kernel/cpu/common.c
> >> +++ b/arch/x86/kernel/cpu/common.c
> >> @@ -1005,14 +1005,6 @@ void enable_sep_cpu(void)
> >>       if (IS_ENABLED(CONFIG_X86_32) && !boot_cpu_has(X86_FEATURE_SEP))
> >>               goto out;
> >>
> >> -#ifdef CONFIG_X86_32
> >> -     /*
> >> -      * We cache MSR_IA32_SYSENTER_CS's value in the TSS's ss1 field --
> >> -      * see the big comment in struct x86_hw_tss's definition.
> >> -      */
> >> -     tss->x86_tss.ss1 = __KERNEL_CS;
> >> -#endif
> >> -
> >>       wrmsrl_safe(MSR_IA32_SYSENTER_CS, __KERNEL_CS);
> >>       wrmsrl_safe(MSR_IA32_SYSENTER_ESP,
> >>                   (unsigned long)tss +
> >
> > So this code changed substantially in tip:x86/asm - do we still need this patch?
> >
> 
> Yes, although I think it's actually the other way around -- I think
> this patch may have applied on top of something that never made it
> into tip/x86/asm.  I can re-check or I could just rebase the patch (or
> you could apply it with the obvious fixup).

Yeah, so I noticed that it fell amongst the cracks - please incorporate it into 
your next (v4.4 targeted) series once we get to that, so it doesn't get lost.

> It's obviously not a critical fix.

Yeah.

Thanks,

	Ingo
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