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From a57e456a7b28431b55e407e5ab78ebd5b378d19e Mon Sep 17 00:00:00 2001
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From: Thomas Gleixner <tglx@linutronix.de>
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Date: Sat, 22 Aug 2015 16:41:17 +0200
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Subject: [PATCH] x86/apic: Fix fallout from x2apic cleanup
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In the recent x2apic cleanup I got two things really wrong:
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1) The safety check in __disable_x2apic which allows the function to
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be called unconditionally is backwards. The check is there to
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prevent access to the apic MSR in case that the machine has no
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apic. Though right now it returns if the machine has an apic and
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therefor the disabling of x2apic is never invoked.
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2) x2apic_disable() sets x2apic_mode to 0 after registering the local
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apic. That's wrong, because register_lapic_address() checks x2apic
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mode and therefor takes the wrong code path.
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This results in boot failures on machines with x2apic preenabled by
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BIOS and can also lead to an fatal MSR access on machines without
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apic.
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The solutions are simple:
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1) Correct the sanity check for apic availability
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2) Clear x2apic_mode _before_ calling register_lapic_address()
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Fixes: 659006bf3ae3 'x86/x2apic: Split enable and setup function'
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Reported-and-tested-by: Javier Monteagudo <javiermon@gmail.com>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Link: https://bugzilla.redhat.com/show_bug.cgi?id=1224764
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Cc: stable@vger.kernel.org # 4.0+
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Cc: Laura Abbott <labbott@redhat.com>
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Cc: Jiang Liu <jiang.liu@linux.intel.com>
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Cc: Joerg Roedel <joro@8bytes.org>
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Cc: Tony Luck <tony.luck@intel.com>
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Cc: Borislav Petkov <bp@alien8.de>
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---
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arch/x86/kernel/apic/apic.c | 14 +++++++-------
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1 file changed, 7 insertions(+), 7 deletions(-)
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diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
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index dcb5285..cde732c 100644
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--- a/arch/x86/kernel/apic/apic.c
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+++ b/arch/x86/kernel/apic/apic.c
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@@ -1424,7 +1424,7 @@ static inline void __x2apic_disable(void)
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{
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u64 msr;
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- if (cpu_has_apic)
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+ if (!cpu_has_apic)
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return;
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rdmsrl(MSR_IA32_APICBASE, msr);
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@@ -1483,10 +1483,13 @@ void x2apic_setup(void)
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static __init void x2apic_disable(void)
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{
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- u32 x2apic_id;
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+ u32 x2apic_id, state = x2apic_state;
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- if (x2apic_state != X2APIC_ON)
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- goto out;
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+ x2apic_mode = 0;
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+ x2apic_state = X2APIC_DISABLED;
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+
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+ if (state != X2APIC_ON)
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+ return;
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x2apic_id = read_apic_id();
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if (x2apic_id >= 255)
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@@ -1494,9 +1497,6 @@ static __init void x2apic_disable(void)
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__x2apic_disable();
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register_lapic_address(mp_lapic_addr);
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-out:
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- x2apic_state = X2APIC_DISABLED;
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- x2apic_mode = 0;
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}
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static __init void x2apic_enable(void)
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--
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2.4.3
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