linux-kernel - [PATCH] x86/apic: Silence "FW_BUG TSC_DEADLINE disabled due to Errata" on hypervisors

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Date:   Tue, 10 Oct 2017 12:12:57 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     x86@...nel.org, Hans de Goede <hdegoede@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, stable@...r.kernel.org
Subject: [PATCH] x86/apic: Silence "FW_BUG TSC_DEADLINE disabled due to Errata" on hypervisors

Commit 594a30fb1242 ("x86/apic: Silence "FW_BUG TSC_DEADLINE disabled
due to Errata" on CPUs without the feature", 2017-08-30) was also about
silencing the warning on VirtualBox; however, KVM does expose the TSC
deadline time, and it's virtualized so that it is immune from CPU errata.

Therefore, booting 4.13 with "-cpu Haswell" shows this in the logs:

     [    0.000000] [Firmware Bug]: TSC_DEADLINE disabled due to Errata;
                    please update microcode to version: 0xb2 (or later)

Even if you had a hypervisor that does _not_ virtualize the TSC deadline
and rather exposes the hardware one, it should be the hypervisor's task
to update microcode and possibly hide the flag from CPUID.  So just
hide the message when running on _any_ hypervisor, not just those that
do not support the TSC deadline timer.

The older check still makes sense, so keep it.

Cc: Hans de Goede <hdegoede@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: stable@...r.kernel.org
Fixes: bd9240a18e ("x86/apic: Add TSC_DEADLINE quirk due to errata")
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kernel/apic/apic.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index d705c769f77d..50109eae8cd7 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -600,7 +600,8 @@ static void apic_check_deadline_errata(void)
 	const struct x86_cpu_id *m;
 	u32 rev;

-	if (!boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER))
+	if (!boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER) ||
+	    boot_cpu_has(X86_FEATURE_HYPERVISOR))
 		return;

 	m = x86_match_cpu(deadline_match);
-- 
1.8.3.1