linux-kernel - [tip:x86/urgent] x86/vmware: Skip lapic calibration on VMware

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Message-ID: <tip-b91688f528fe96e09d17e6d87c1b2805eb0c445e@git.kernel.org>
Date:   Wed, 5 Oct 2016 02:49:28 -0700
From:   tip-bot for Renat Valiullin <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, akataria@...are.com, rvaliullin@...are.com,
        mingo@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject: [tip:x86/urgent] x86/vmware: Skip lapic calibration on VMware

Commit-ID:  b91688f528fe96e09d17e6d87c1b2805eb0c445e
Gitweb:     http://git.kernel.org/tip/b91688f528fe96e09d17e6d87c1b2805eb0c445e
Author:     Renat Valiullin <rvaliullin@...are.com>
AuthorDate: Tue, 4 Oct 2016 13:11:48 -0700
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Wed, 5 Oct 2016 11:43:30 +0200

x86/vmware: Skip lapic calibration on VMware

In a virtualized environment the APIC timer calibration can go wrong when
the host is overcommitted or the guest is running nested. This results
in the APIC timers operating at an incorrect frequency.

Since VMware supports a mechanism to retrieve the local APIC frequency we
can ask the hypervisor for it and skip the APIC calibration loop.

Signed-off-by: Renat Valiullin <rvaliullin@...are.com>
Acked-by: Alok N Kataria <akataria@...are.com>
Cc: virtualization@...ts.linux-foundation.org
Link: http://lkml.kernel.org/r/20161004201148.GA1421@uu64vm
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

---
 arch/x86/kernel/cpu/vmware.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
index 1ff0598..8116057 100644
--- a/arch/x86/kernel/cpu/vmware.c
+++ b/arch/x86/kernel/cpu/vmware.c
@@ -27,6 +27,7 @@
 #include <asm/div64.h>
 #include <asm/x86_init.h>
 #include <asm/hypervisor.h>
+#include <asm/apic.h>
 
 #define CPUID_VMWARE_INFO_LEAF	0x40000000
 #define VMWARE_HYPERVISOR_MAGIC	0x564D5868
@@ -82,10 +83,17 @@ static void __init vmware_platform_setup(void)
 
 	VMWARE_PORT(GETHZ, eax, ebx, ecx, edx);
 
-	if (ebx != UINT_MAX)
+	if (ebx != UINT_MAX) {
 		x86_platform.calibrate_tsc = vmware_get_tsc_khz;
-	else
+#ifdef CONFIG_X86_LOCAL_APIC
+		/* Skip lapic calibration since we know the bus frequency. */
+		lapic_timer_frequency = ecx / HZ;
+		pr_info("Host bus clock speed read from hypervisor : %u Hz\n",
+			ecx);
+#endif
+	} else {
 		pr_warn("Failed to get TSC freq from the hypervisor\n");
+	}
 }
 
 /*