linux-kernel - [RFC PATCH v3 14/21] KVM: x86: Kill cur_tsc

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Date: Wed, 22 May 2024 01:17:09 +0100
From: David Woodhouse <dwmw2@...radead.org>
To: kvm@...r.kernel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>,
	Jonathan Corbet <corbet@....net>,
	Sean Christopherson <seanjc@...gle.com>,
	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,
	"H. Peter Anvin" <hpa@...or.com>,
	Paul Durrant <paul@....org>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>,
	Shuah Khan <shuah@...nel.org>,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	jalliste@...zon.co.uk,
	sveith@...zon.de,
	zide.chen@...el.com,
	Dongli Zhang <dongli.zhang@...cle.com>,
	Chenyi Qiang <chenyi.qiang@...el.com>
Subject: [RFC PATCH v3 14/21] KVM: x86: Kill cur_tsc_{nsec,offset,write} fields

From: David Woodhouse <dwmw@...zon.co.uk>

These pointlessly duplicate the last_tsc_{nsec,offset,write} values.

The only place they were used was where the TSC is stable and a new vCPU
is being synchronized to the previous setting, in which case the 'last_'
value is definitely identical.

Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
---
 arch/x86/include/asm/kvm_host.h |  3 ---
 arch/x86/kvm/x86.c              | 19 ++++++++-----------
 2 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index b01c1d000fff..7d06f389a607 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1354,9 +1354,6 @@ struct kvm_arch {
 	u32 last_tsc_khz;
 	u64 last_tsc_offset;
 	u64 last_tsc_scaling_ratio;
-	u64 cur_tsc_nsec;
-	u64 cur_tsc_write;
-	u64 cur_tsc_offset;
 	u64 cur_tsc_generation;
 	int nr_vcpus_matched_tsc;
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6ec43f39bdb0..ab5d55071253 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2713,11 +2713,9 @@ static void __kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 offset, u64 tsc,
 	lockdep_assert_held(&kvm->arch.tsc_write_lock);
 
 	/*
-	 * We also track th most recent recorded KHZ, write and time to
-	 * allow the matching interval to be extended at each write.
+	 * Track the last recorded kHz (and associated scaling ratio for
+	 * calculating the guest TSC), and offset.
 	 */
-	kvm->arch.last_tsc_nsec = ns;
-	kvm->arch.last_tsc_write = tsc;
 	kvm->arch.last_tsc_khz = vcpu->arch.virtual_tsc_khz;
 	kvm->arch.last_tsc_scaling_ratio = vcpu->arch.l1_tsc_scaling_ratio;
 	kvm->arch.last_tsc_offset = offset;
@@ -2736,10 +2734,9 @@ static void __kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 offset, u64 tsc,
 		 *
 		 * These values are tracked in kvm->arch.cur_xxx variables.
 		 */
+		kvm->arch.last_tsc_nsec = ns;
+		kvm->arch.last_tsc_write = tsc;
 		kvm->arch.cur_tsc_generation++;
-		kvm->arch.cur_tsc_nsec = ns;
-		kvm->arch.cur_tsc_write = tsc;
-		kvm->arch.cur_tsc_offset = offset;
 		kvm->arch.nr_vcpus_matched_tsc = 0;
 	} else if (vcpu->arch.this_tsc_generation != kvm->arch.cur_tsc_generation) {
 		kvm->arch.nr_vcpus_matched_tsc++;
@@ -2747,8 +2744,8 @@ static void __kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 offset, u64 tsc,
 
 	/* Keep track of which generation this VCPU has synchronized to */
 	vcpu->arch.this_tsc_generation = kvm->arch.cur_tsc_generation;
-	vcpu->arch.this_tsc_nsec = kvm->arch.cur_tsc_nsec;
-	vcpu->arch.this_tsc_write = kvm->arch.cur_tsc_write;
+	vcpu->arch.this_tsc_nsec = kvm->arch.last_tsc_nsec;
+	vcpu->arch.this_tsc_write = kvm->arch.last_tsc_write;
 
 	kvm_track_tsc_matching(vcpu);
 }
@@ -2825,8 +2822,8 @@ static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 *user_value)
 		data = kvm->arch.last_tsc_write;
 
 		if (!kvm_check_tsc_unstable()) {
-			offset = kvm->arch.cur_tsc_offset;
-			ns = kvm->arch.cur_tsc_nsec;
+			offset = kvm->arch.last_tsc_offset;
+			ns = kvm->arch.last_tsc_nsec;
 		} else {
 			/*
 			 * ... unless the TSC is unstable and has to be
-- 
2.44.0