From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f197.google.com (mail-pg1-f197.google.com [209.85.215.197]) (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 C370148987A for ; Wed, 26 Aug 2026 21:33:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.197 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787779989; cv=none; b=l4qLXqJ2lGitSEF60Kgyg+qEQLMq8C4Yvq3yvSMlTuFQukvjtNC92kMZrGeW5KDQkhx+4kWJ8KdWHOwZRpXgGuT+I9Rp7Dedg2K6Brue/0Q8dAp1LynxIuT4styzBeMp/0wdTpA1e7jMo+pUyTr+v4P68LxWCVfKYS4SzE2LjCI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787779989; c=relaxed/simple; bh=oyP3Jx5TwpM7lfELbNHOfyWPzvuct03eZ43EbbHjfho=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=He8SieoP3dctBEul0Pb2beh1C6hUIJkfvkpPlk6ztbfL2TEaytDQ+uv1HU6Hoxf7sFB/egoBZiAGPRgq9md6RAhKRORX4Y6Spltyu0l1VJ2bDS1jwLPU9OVES5b2JybkUXLZ5JtHG3lqRWB0U2RDokqfWFj/cf4/Ii8FE+U/vSA= 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=LhwBOzJQ; arc=none smtp.client-ip=209.85.215.197 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="LhwBOzJQ" Received: by mail-pg1-f197.google.com with SMTP id 41be03b00d2f7-cc1b80835d5so1618652a12.2 for ; Wed, 26 Aug 2026 14:33:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1787779987; x=1788384787; 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=SS97OA+o28099dnvzUD8Vv8IMBV5k83CG9rDEZqRG/8=; b=LhwBOzJQGYv359CevPYPq1TEGh8vUbBvQ7eg72os7QFgGLY7RHUd/U1zh2NBDS3Zzt OEDXbQdEDpAgsIzJK/Mmk4z0s8nr+4YUsCLsBK1fbyX2ejU+g4oVkqowUOTdowi5EkRH P57h82UbFDYsit0rm+eghfCRgnVff8Op67+WYOyXyVEK/doa/ycu8x1hGQbyVYwsSnIY toxeQM9I68KlKbjsRReUiN8NQsExheP6GzZtuhhxJgCFYJg+l71xzURH56JHetXLsUF8 IGjrw4I68DuXt5eEzabx6f+Xr2u1/dG9TYXTu9XnYp2PK/cDf5D9VJKrdy0axJUeB9D1 Z8kA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1787779987; x=1788384787; 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=SS97OA+o28099dnvzUD8Vv8IMBV5k83CG9rDEZqRG/8=; b=S7hTFhS7yhLf3jzkCug5qofl324Io22cB6N1R2LNQ1+wLAxaesfX+qnIDyXniRJPsr QM1+ARoIG0OTXJpregjuziHqaiPdivQv/fFxYx2sVOwiyue1a8yNxAcYzNhXMoOcfPPU 4UPlxraeVEVY+ZoomZDHDg5JK+xuknZULJ5EMxqyGQhZdgEW6Xh0Ed807NVnOrMqgoAn m6yl1WuU+oEo7PbRBxr/b3FbuiN+RP/rCYuWPrL3k2lY8nhR/9+CqrZtcsYMccgqu3gc JUVwY13nPmE6NbF0clWO6NHY6akuljgLnLLUnwNloK7w8qNVzqdkdgUbtDT0G6Ua4JpQ n8Xg== X-Gm-Message-State: AFuF++mZP6RSK1E+7R6nkpLb7R9dxDzBAUnzjKWirs5SwLjtQmwkIq4C OkXn4RYF2SGSiXA7H2Y1v3y2PTpfOM8fx5f2sYcIqNRzOxeRhtvp/C2og+bHkmSuKzbiM6GWlBS zB8Aeng== X-Received: from pgal4.prod.google.com ([2002:a63:3e04:0:b0:cc1:be9e:35ef]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:a95:b0:3c1:fbf:1e2e with SMTP id adf61e73a8af0-3cf83b22768mr21020948637.10.1787779986926; Wed, 26 Aug 2026 14:33:06 -0700 (PDT) Reply-To: Sean Christopherson Date: Wed, 26 Aug 2026 14:32:42 -0700 In-Reply-To: <20260826213303.914988-1-seanjc@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260826213303.914988-1-seanjc@google.com> X-Mailer: git-send-email 2.55.0.887.g758fc8c411-goog Message-ID: <20260826213303.914988-3-seanjc@google.com> Subject: [PATCH v10 02/21] 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. 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 | 1 + arch/x86/kvm/x86.c | 18 ++++++++++-------- 3 files changed, 12 insertions(+), 9 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 683bb8bf43a9..0255ca6b24c2 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 ddb022cb203a..ca26be88c204 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -16,6 +16,7 @@ #include #include #include +#include #include #include diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 10f11e06d117..e18158f51103 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; -- 2.55.0.887.g758fc8c411-goog