linux-kernel - [PATCH v12 16/19] x86/kvmclock: Use clock source callback to update kvm sched clock

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: <20241009092850.197575-17-nikunj@amd.com>
Date: Wed, 9 Oct 2024 14:58:47 +0530
From: Nikunj A Dadhania <nikunj@....com>
To: <linux-kernel@...r.kernel.org>, <thomas.lendacky@....com>, <bp@...en8.de>,
	<x86@...nel.org>, <kvm@...r.kernel.org>
CC: <mingo@...hat.com>, <tglx@...utronix.de>, <dave.hansen@...ux.intel.com>,
	<pgonda@...gle.com>, <seanjc@...gle.com>, <pbonzini@...hat.com>,
	<nikunj@....com>
Subject: [PATCH v12 16/19] x86/kvmclock: Use clock source callback to update kvm sched clock

Although the kernel switches over to stable TSC clocksource instead of
kvmclock, the scheduler still keeps on using kvmclock as the sched clock.
This is due to kvm_sched_clock_init() updating the pv_sched_clock()
unconditionally.

Use the clock source enable/disable callbacks to initialize
kvm_sched_clock_init() and update the pv_sched_clock().

As the clock selection happens in the stop machine context, schedule
delayed work to update the static_call()

Signed-off-by: Nikunj A Dadhania <nikunj@....com>
---
 arch/x86/kernel/kvmclock.c | 34 +++++++++++++++++++++++++++++-----
 1 file changed, 29 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index 5b2c15214a6b..5cd3717e103b 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -21,6 +21,7 @@
 #include <asm/hypervisor.h>
 #include <asm/x86_init.h>
 #include <asm/kvmclock.h>
+#include <asm/timer.h>
 
 static int kvmclock __initdata = 1;
 static int kvmclock_vsyscall __initdata = 1;
@@ -148,12 +149,39 @@ bool kvm_check_and_clear_guest_paused(void)
 	return ret;
 }
 
+static u64 (*old_pv_sched_clock)(void);
+
+static void enable_kvm_sc_work(struct work_struct *work)
+{
+	u8 flags;
+
+	old_pv_sched_clock = static_call_query(pv_sched_clock);
+	flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
+	kvm_sched_clock_init(flags & PVCLOCK_TSC_STABLE_BIT);
+}
+
+static DECLARE_DELAYED_WORK(enable_kvm_sc, enable_kvm_sc_work);
+
+static void disable_kvm_sc_work(struct work_struct *work)
+{
+	if (old_pv_sched_clock)
+		paravirt_set_sched_clock(old_pv_sched_clock);
+}
+static DECLARE_DELAYED_WORK(disable_kvm_sc, disable_kvm_sc_work);
+
 static int kvm_cs_enable(struct clocksource *cs)
 {
 	vclocks_set_used(VDSO_CLOCKMODE_PVCLOCK);
+	schedule_delayed_work(&enable_kvm_sc, 0);
+
 	return 0;
 }
 
+static void kvm_cs_disable(struct clocksource *cs)
+{
+	schedule_delayed_work(&disable_kvm_sc, 0);
+}
+
 static struct clocksource kvm_clock = {
 	.name	= "kvm-clock",
 	.read	= kvm_clock_get_cycles,
@@ -162,6 +190,7 @@ static struct clocksource kvm_clock = {
 	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
 	.id     = CSID_X86_KVM_CLK,
 	.enable	= kvm_cs_enable,
+	.disable = kvm_cs_disable,
 };
 
 static void kvm_register_clock(char *txt)
@@ -287,8 +316,6 @@ static int kvmclock_setup_percpu(unsigned int cpu)
 
 void __init kvmclock_init(void)
 {
-	u8 flags;
-
 	if (!kvm_para_available() || !kvmclock)
 		return;
 
@@ -317,9 +344,6 @@ void __init kvmclock_init(void)
 	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))
 		pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);
 
-	flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
-	kvm_sched_clock_init(flags & PVCLOCK_TSC_STABLE_BIT);
-
 	x86_platform.calibrate_tsc = kvm_get_tsc_khz;
 	x86_platform.calibrate_cpu = kvm_get_tsc_khz;
 	x86_platform.get_wallclock = kvm_get_wallclock;
-- 
2.34.1