linux-kernel - Re: [PATCH] [4/7] Convert TSC disabling to generic cpuid disable bitmap

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Message-Id: <1200766712.32050.35.camel@cthulhu.hellion.org.uk>
Date:	Sat, 19 Jan 2008 18:18:32 +0000
From:	Ian Campbell <ijc@...lion.org.uk>
To:	Andi Kleen <ak@...e.de>
Cc:	mingo@...e.hu, hpa@...or.com, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH] [4/7] Convert TSC disabling to generic cpuid disable
	bitmap

Should have added Jeremy to CC, sorry for the duplicate message.

On Fri, 2008-01-18 at 18:27 +0100, Andi Kleen wrote:
> Index: linux/arch/x86/xen/time.c
> ===================================================================
> --- linux.orig/arch/x86/xen/time.c
> +++ linux/arch/x86/xen/time.c
> @@ -592,7 +592,7 @@ __init void xen_time_init(void)
>         set_normalized_timespec(&wall_to_monotonic,
>                                 -xtime.tv_sec, -xtime.tv_nsec);
>  
> -       tsc_disable = 0;
> +       setup_clear_cpu_cap(X86_FEATURE_TSC);
>  
>         xen_setup_timer(cpu);
>         xen_setup_cpu_clockevents();

That inverts the meaning, doesn't it? Previously the code force the TSC
to be on and now it forcefully disables it. Now when booting a Xen guest
I get:
        Kernel panic - not syncing: Kernel compiled for Pentium+, requires TSC feature!

I think you want something like the following
---
>>From eab0f03f2659670673496b48c03c0f79151e7bbf Mon Sep 17 00:00:00 2001
From: Ian Campbell <ijc@...lion.org.uk>
Date: Sat, 19 Jan 2008 18:08:23 +0000
Subject: [PATCH] x86: Xen requires TSC support to be forced on, not disabled.

Signed-off-by: Ian Campbell <ijc@...lion.org.uk>
---
 arch/x86/xen/time.c          |    2 +-
 include/asm-x86/cpufeature.h |    4 ++++
 2 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 6f5c74a..b3721fd 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -592,7 +592,7 @@ __init void xen_time_init(void)
 	set_normalized_timespec(&wall_to_monotonic,
 				-xtime.tv_sec, -xtime.tv_nsec);
 
-	setup_clear_cpu_cap(X86_FEATURE_TSC);
+	setup_force_cpu_cap(X86_FEATURE_TSC);
 
 	xen_setup_timer(cpu);
 	xen_setup_cpu_clockevents();
diff --git a/include/asm-x86/cpufeature.h b/include/asm-x86/cpufeature.h
index 91a7665..b6f969c 100644
--- a/include/asm-x86/cpufeature.h
+++ b/include/asm-x86/cpufeature.h
@@ -135,6 +135,10 @@
 	clear_cpu_cap(&boot_cpu_data, bit);	\
 	set_bit(bit, cleared_cpu_caps); 	\
 } while (0)
+#define setup_force_cpu_cap(bit) do { \
+	set_cpu_cap(&boot_cpu_data, bit);	\
+	clear_bit(bit, cleared_cpu_caps); 	\
+} while (0)
 
 #define cpu_has_fpu		boot_cpu_has(X86_FEATURE_FPU)
 #define cpu_has_vme		boot_cpu_has(X86_FEATURE_VME)
-- 
1.5.3.8


-- 
Ian Campbell

All that glitters is not gold; all that wander are not lost.

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