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From: David Woodhouse <dwmw2@infradead.org>
To: kvm@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>,
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	Sean Christopherson <seanjc@google.com>,
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	jalliste@amazon.co.uk,
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	Dongli Zhang <dongli.zhang@oracle.com>,
	Chenyi Qiang <chenyi.qiang@intel.com>
Subject: [RFC PATCH v3 14/21] KVM: x86: Kill cur_tsc_{nsec,offset,write} fields
Date: Wed, 22 May 2024 01:17:09 +0100
Message-ID: <20240522001817.619072-15-dwmw2@infradead.org>
In-Reply-To: <20240522001817.619072-1-dwmw2@infradead.org>
References: <20240522001817.619072-1-dwmw2@infradead.org>
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Sender: David Woodhouse <dwmw2@infradead.org>

From: David Woodhouse <dwmw@amazon.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@amazon.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