From a4497a86fb9b855c5ac8503fdc959393b00bb643 Mon Sep 17 00:00:00 2001 From: Prarit Bhargava Date: Thu, 8 Sep 2016 10:15:28 -0400 Subject: [PATCH] x86, clock: Fix kvm guest tsc initialization MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit When booting a kvm guest on AMD with the latest kernel the following messages are displayed in the boot log: tsc: Unable to calibrate against PIT tsc: HPET/PMTIMER calibration failed aa297292d708 ("x86/tsc: Enumerate SKL cpu_khz and tsc_khz via CPUID") introduced a change to account for a difference in cpu and tsc frequencies for Intel SKL processors. Before this change the native tsc set x86_platform.calibrate_tsc to native_calibrate_tsc() which is a hardware calibration of the tsc, and in tsc_init() executed tsc_khz = x86_platform.calibrate_tsc(); cpu_khz = tsc_khz; The kvm code changed x86_platform.calibrate_tsc to kvm_get_tsc_khz() and executed the same tsc_init() function. This meant that KVM guests did not execute the native hardware calibration function. After aa297292d708, there are separate native calibrations for cpu_khz and tsc_khz. The code sets x86_platform.calibrate_tsc to native_calibrate_tsc() which is now an Intel specific calibration function, and x86_platform.calibrate_cpu to native_calibrate_cpu() which is the "old" native_calibrate_tsc() function (ie, the native hardware calibration function). tsc_init() now does cpu_khz = x86_platform.calibrate_cpu(); tsc_khz = x86_platform.calibrate_tsc(); if (tsc_khz == 0) tsc_khz = cpu_khz; else if (abs(cpu_khz - tsc_khz) * 10 > tsc_khz) cpu_khz = tsc_khz; The kvm code should not call the hardware initialization in native_calibrate_cpu(), as it isn't applicable for kvm and it didn't do that prior to aa297292d708. This patch resolves this issue by setting x86_platform.calibrate_cpu to kvm_get_tsc_khz(). v2: I had originally set x86_platform.calibrate_cpu to cpu_khz_from_cpuid(), however, pbonzini pointed out that the CPUID leaf in that function is not available in KVM. I have changed the function pointer to kvm_get_tsc_khz(). Fixes: aa297292d708 ("x86/tsc: Enumerate SKL cpu_khz and tsc_khz via CPUID") Signed-off-by: Prarit Bhargava Cc: Paolo Bonzini Cc: Radim Krčmář Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: x86@kernel.org Cc: Len Brown Cc: "Peter Zijlstra (Intel)" Cc: Borislav Petkov Cc: Adrian Hunter Cc: "Christopher S. Hall" Cc: David Woodhouse Cc: kvm@vger.kernel.org Signed-off-by: Paolo Bonzini --- arch/x86/kernel/kvmclock.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c index 1d39bfbd26bb..3692249a70f1 100644 --- a/arch/x86/kernel/kvmclock.c +++ b/arch/x86/kernel/kvmclock.c @@ -289,6 +289,7 @@ void __init kvmclock_init(void) put_cpu(); x86_platform.calibrate_tsc = kvm_get_tsc_khz; + x86_platform.calibrate_cpu = kvm_get_tsc_khz; x86_platform.get_wallclock = kvm_get_wallclock; x86_platform.set_wallclock = kvm_set_wallclock; #ifdef CONFIG_X86_LOCAL_APIC -- 2.30.2