linux-kernel - [PATCH 10/16] x86/paravirt: Move handling of unstable PV clocks into paravirt_set_sched

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Message-ID: <20250201021718.699411-11-seanjc@google.com>
Date: Fri, 31 Jan 2025 18:17:12 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Juergen Gross <jgross@...e.com>, 
	"K. Y. Srinivasan" <kys@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, 
	Dexuan Cui <decui@...rosoft.com>, Ajay Kaher <ajay.kaher@...adcom.com>, 
	Alexey Makhalov <alexey.amakhalov@...adcom.com>, Jan Kiszka <jan.kiszka@...mens.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Andy Lutomirski <luto@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, linux-coco@...ts.linux.dev, 
	virtualization@...ts.linux.dev, linux-hyperv@...r.kernel.org, 
	jailhouse-dev@...glegroups.com, kvm@...r.kernel.org, 
	xen-devel@...ts.xenproject.org, Sean Christopherson <seanjc@...gle.com>, 
	Nikunj A Dadhania <nikunj@....com>, Tom Lendacky <thomas.lendacky@....com>
Subject: [PATCH 10/16] x86/paravirt: Move handling of unstable PV clocks into paravirt_set_sched_clock()

Move the handling of unstable PV clocks, of which kvmclock is the only
example, into paravirt_set_sched_clock().  This will allow modifying
paravirt_set_sched_clock() to keep using the TSC for sched_clock in
certain scenarios without unintentionally marking the TSC-based clock as
unstable.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/include/asm/paravirt.h | 7 ++++++-
 arch/x86/kernel/kvmclock.c      | 5 +----
 arch/x86/kernel/paravirt.c      | 6 +++++-
 3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 041aff51eb50..cfceabd5f7e1 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -28,7 +28,12 @@ u64 dummy_sched_clock(void);
 DECLARE_STATIC_CALL(pv_steal_clock, dummy_steal_clock);
 DECLARE_STATIC_CALL(pv_sched_clock, dummy_sched_clock);
 
-void paravirt_set_sched_clock(u64 (*func)(void));
+void __paravirt_set_sched_clock(u64 (*func)(void), bool stable);
+
+static inline void paravirt_set_sched_clock(u64 (*func)(void))
+{
+	__paravirt_set_sched_clock(func, true);
+}
 
 static __always_inline u64 paravirt_sched_clock(void)
 {
diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index b41ac7f27b9f..890535ddc059 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -12,7 +12,6 @@
 #include <linux/hardirq.h>
 #include <linux/cpuhotplug.h>
 #include <linux/sched.h>
-#include <linux/sched/clock.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/set_memory.h>
@@ -93,10 +92,8 @@ static noinstr u64 kvm_sched_clock_read(void)
 
 static inline void kvm_sched_clock_init(bool stable)
 {
-	if (!stable)
-		clear_sched_clock_stable();
 	kvm_sched_clock_offset = kvm_clock_read();
-	paravirt_set_sched_clock(kvm_sched_clock_read);
+	__paravirt_set_sched_clock(kvm_sched_clock_read, stable);
 
 	pr_info("kvm-clock: using sched offset of %llu cycles",
 		kvm_sched_clock_offset);
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 1ccaa3397a67..55c819673a9d 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -14,6 +14,7 @@
 #include <linux/highmem.h>
 #include <linux/kprobes.h>
 #include <linux/pgtable.h>
+#include <linux/sched/clock.h>
 #include <linux/static_call.h>
 
 #include <asm/bug.h>
@@ -85,8 +86,11 @@ static u64 native_steal_clock(int cpu)
 DEFINE_STATIC_CALL(pv_steal_clock, native_steal_clock);
 DEFINE_STATIC_CALL(pv_sched_clock, native_sched_clock);
 
-void paravirt_set_sched_clock(u64 (*func)(void))
+void __paravirt_set_sched_clock(u64 (*func)(void), bool stable)
 {
+	if (!stable)
+		clear_sched_clock_stable();
+
 	static_call_update(pv_sched_clock, func);
 }
 
-- 
2.48.1.362.g079036d154-goog