From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5F4723EFFB4 for ; Tue, 4 Aug 2026 23:39:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785886770; cv=none; b=X6MLF0iTR6s5SiFCuU5b5HAsVQO2mdUfBHouTN7HYqXWe8dfS0HQv4yXEH8lPDEViBbQe2BXaLVeE4Wvlsy4nvtVXc96qkFV/0JgVCmznel0WCegQGUnnNBzTqZysvtgDhYN6L1VEqn4Ir+/yL5ckF0T0LjUk1BQqe2wrHC3mUQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785886770; c=relaxed/simple; bh=VcDFsyXNDS5AHqe/iR4hiX/uBj74+UXKYzqXs5zgolM=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=mswb6QgymXqgDjiDFGxtoi7J4ZvDipO1PceTj+XFycGurUyxE/CUZhvAVwMD2LyDIhe2fzovpzjLozDLreRYmvkVXi7A6ZmaQ8+38bGKtHeIeBi85UlYxjR/TV83GdbaENacvazZKSpZPx4PHEtFmqP2KjunHzaueMr5IbU9MlI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=I6hlMLUu; arc=none smtp.client-ip=209.85.215.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="I6hlMLUu" Received: by mail-pg1-f199.google.com with SMTP id 41be03b00d2f7-cb48f41343aso1184240a12.1 for ; Tue, 04 Aug 2026 16:39:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1785886769; x=1786491569; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:reply-to:from:to:cc:subject:date:message-id :reply-to:content-type; bh=3GRGf0SAx8ZhbJ78r2siXWKgWBaDw4VeY+GDZV2SFCo=; b=I6hlMLUuVXe6DHnG+lI293LZZvFJohQ4wpp3q333dVSas0Sh+/UtCVNCgc/OAQHhpg PmyRfEgl5msRwo96d/qhbeoOLkD76uv0HHSnT2vKKeBhhvNm1ls9y7gJVYoJKMnxIA4L 1aUmoHAsxzjHzssm12jIg/WiK/kcYzx3V3WIL4QL3p7WgDdO0OSlB9VdfXZfonPZdRVB +eO83wKmUUv6qrkiqv4RrZDhNjiRdQnksNDEREhYpptiEzApMdUypGyLmhi76DLWF1q5 gUFlvBNjXJrtYws096vE+jalrIR3mTKTH5W6swJkhWG+c1WGVufxk6ssJ+yHO+J6Oo6O Mwrg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1785886769; x=1786491569; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:reply-to:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to:content-type; bh=3GRGf0SAx8ZhbJ78r2siXWKgWBaDw4VeY+GDZV2SFCo=; b=EPsQuX6e6Ceqpi41XNQasO3+isXlSnNFuVL+8wlLuV8EGv0h7WhZ0sR5PlIflES8gu uKxjT8sWdIO7uVEtUHQk+fBcQJ8FCqyRnhOI43d0+myWcnCZO50W+dPEgeHn8jK9WFjT nUMh44AreiU4Y4oIwX/41OpKVJm8Qq8xBgy2m4VViIfpc2C5uCGGAMcFN2traWoJ5UUB 6r/KFVadngC75m9cSwf5Vdfclortj1RFSO0PAwHMHVl692nc8M3FAzyJ+8hxqaqzIch0 7WYYhO+HjxMe8RhG5z3hAgS8PjbkGV1rxMy0TQlzfP9ZgbQozq+CN5uV7ZOGEHqyPX4U bEIA== X-Forwarded-Encrypted: i=1; AHgh+RrGHVAyYvvaFizyrDHHkMgwl1NI38DR+hkmqxDXu4IZSpD2j3RSTWWgibjoc5OJIyFViTx9KoG1Mvd6hOs=@vger.kernel.org X-Gm-Message-State: AOJu0Yx/Dj+QPGCHH1nJZZLttRxTuau4ch1eLS7UN8RdZA83b7/XfeNL AiXaLmRfPwLrbEtS1ZkGQN19xflDYj3AuLdhyzwVS7uO76Fv5QIj0DgbUKAyXJeCzC3rf5LBlDG SyocSig== X-Received: from pjhk65.prod.google.com ([2002:a17:90a:4cc7:b0:381:6cb1:3289]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:4e8d:b0:38e:5828:a446 with SMTP id 98e67ed59e1d1-3903c70ae1bmr1050461a91.19.1785886768582; Tue, 04 Aug 2026 16:39:28 -0700 (PDT) Reply-To: Sean Christopherson Date: Tue, 4 Aug 2026 16:39:06 -0700 In-Reply-To: <20260804233923.3504629-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260804233923.3504629-1-seanjc@google.com> X-Mailer: git-send-email 2.55.0.571.g244d577d93-goog Message-ID: <20260804233923.3504629-3-seanjc@google.com> Subject: [PATCH v8 02/17] KVM: x86: Improve accuracy of KVM clock when TSC scaling is in force From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Paul Durrant , David Woodhouse , Dongli Zhang Content-Type: text/plain; charset="UTF-8" From: David Woodhouse The kvm_guest_time_update() function scales the host TSC frequency to the guest's using kvm_scale_tsc() and the v->arch.l1_tsc_scaling_ratio scaling ratio previously calculated for that vCPU. Then calculates the scaling factors for the KVM clock itself based on that guest TSC frequency. However, it uses kHz as the unit when scaling, and then multiplies by 1000 only at the end. With a host TSC frequency of 3000MHz and a guest set to 2500MHz, the result of kvm_scale_tsc() will actually come out at 2,499,999kHz. So the KVM clock advertised to the guest is based on a frequency of 2,499,999,000 Hz. By using Hz as the unit from the beginning, the KVM clock would be based on a more accurate frequency of 2,499,999,999 Hz in this example. Use u64 for the hw_tsc_hz field since an unsigned int would overflow for TSC frequencies above 4GHz. Use div_u64() for the Xen CPUID leaf to play nice with 32-bit kernels. Fixes: 78db6a503796 ("KVM: x86: rewrite handling of scaled TSC for kvmclock") Reviewed-by: Paul Durrant Signed-off-by: David Woodhouse Tested-by: Dongli Zhang Signed-off-by: Sean Christopherson --- arch/x86/include/asm/kvm_host.h | 2 +- arch/x86/kvm/cpuid.c | 3 ++- arch/x86/kvm/x86.c | 18 ++++++++++-------- 3 files changed, 13 insertions(+), 10 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 283847619ff8..6ddc988576d0 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -864,7 +864,7 @@ struct kvm_vcpu_arch { gpa_t time; s8 pvclock_tsc_shift; u32 pvclock_tsc_mul; - unsigned int hw_tsc_khz; + u64 hw_tsc_hz; struct gfn_to_pfn_cache pv_time; /* set guest stopped flag in pvclock flags field */ bool pvclock_set_guest_stopped_request; diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 9e9cf6538a96..7049f5a5597b 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -16,6 +16,7 @@ #include #include #include +#include #include #include @@ -2146,7 +2147,7 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, *ecx = vcpu->arch.pvclock_tsc_mul; *edx = vcpu->arch.pvclock_tsc_shift; } else if (index == 2) { - *eax = vcpu->arch.hw_tsc_khz; + *eax = div_u64(vcpu->arch.hw_tsc_hz, HZ_PER_KHZ); } } } else { diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index d3b47e38698c..ce6d155b2ee6 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -61,6 +61,7 @@ #include #include #include +#include #include #include @@ -1763,7 +1764,8 @@ static void kvm_setup_guest_pvclock(struct pvclock_vcpu_time_info *ref_hv_clock, int kvm_guest_time_update(struct kvm_vcpu *v) { struct pvclock_vcpu_time_info hv_clock = {}; - unsigned long flags, tgt_tsc_khz; + unsigned long flags; + u64 tgt_tsc_hz; unsigned seq; struct kvm_vcpu_arch *vcpu = &v->arch; struct kvm_arch *ka = &v->kvm->arch; @@ -1789,8 +1791,8 @@ int kvm_guest_time_update(struct kvm_vcpu *v) /* Keep irq disabled to prevent changes to the clock */ local_irq_save(flags); - tgt_tsc_khz = get_cpu_tsc_khz(); - if (unlikely(tgt_tsc_khz == 0)) { + tgt_tsc_hz = (u64)get_cpu_tsc_khz() * HZ_PER_KHZ; + if (unlikely(tgt_tsc_hz == 0)) { local_irq_restore(flags); kvm_make_request(KVM_REQ_CLOCK_UPDATE, v); return 1; @@ -1831,16 +1833,16 @@ int kvm_guest_time_update(struct kvm_vcpu *v) /* With all the info we got, fill in the values */ if (kvm_caps.has_tsc_control) { - tgt_tsc_khz = kvm_scale_tsc(tgt_tsc_khz, + tgt_tsc_hz = kvm_scale_tsc(tgt_tsc_hz, v->arch.l1_tsc_scaling_ratio); - tgt_tsc_khz = tgt_tsc_khz ? : 1; + tgt_tsc_hz = tgt_tsc_hz ? : 1; } - if (unlikely(vcpu->hw_tsc_khz != tgt_tsc_khz)) { - kvm_get_time_scale(NSEC_PER_SEC, tgt_tsc_khz * 1000LL, + if (unlikely(vcpu->hw_tsc_hz != tgt_tsc_hz)) { + kvm_get_time_scale(NSEC_PER_SEC, tgt_tsc_hz, &vcpu->pvclock_tsc_shift, &vcpu->pvclock_tsc_mul); - vcpu->hw_tsc_khz = tgt_tsc_khz; + vcpu->hw_tsc_hz = tgt_tsc_hz; } hv_clock.tsc_shift = vcpu->pvclock_tsc_shift; -- 2.55.0.571.g244d577d93-goog