linux-kernel - [patch 8/7] x86/kvmclock: Avoid TSC recalibration

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180709092243.GG2476@hirez.programming.kicks-ass.net>
Date:   Mon, 9 Jul 2018 11:22:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        x86@...nel.org, kvm@...r.kernel.org
Subject: [patch 8/7] x86/kvmclock: Avoid TSC recalibration


If the host gives us a TSC rate, assume it is good and don't try and
recalibrate things against virtual timer hardware.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -140,7 +140,16 @@ static inline void kvm_sched_clock_init(
  */
 static unsigned long kvm_get_tsc_khz(void)
 {
-	return pvclock_tsc_khz(this_cpu_pvti());
+	unsigned long tsc_khz = pvclock_tsc_khz(this_cpu_pvti());
+
+	/*
+	 * TSC frequency is reported by the host; calibration against (virtual)
+	 * HPET/PM-timer in a guest is dodgy and pointless since the host already
+	 * did it for us where required.
+	 */
+	setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
+
+	return tsc_khz;
 }
 
 static void kvm_get_preset_lpj(void)