From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f198.google.com (mail-pf1-f198.google.com [209.85.210.198]) (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 617B74A0A18 for ; Thu, 6 Aug 2026 23:36:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.198 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786059413; cv=none; b=GolGcT41zdapm8b/+pVGI32gcr+Kwt6USv/DxeakB5KBT2OQ4MOwTxMqJGHOFbBPthPt32LYMjjVou2DNbT3IrhKvzeFTRWpihRjVRORjMSCGvvLmWqVsPXcdFJFTw9lZMGOFRkq+MuP8c0mJgSvNxtC8ksccPPQMZq87AZC6Z4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786059413; c=relaxed/simple; bh=vnLOYKuncVcjJxpKnUglkawzKiqOPtPepUlhfI+oXJw=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=H0AiQmQoeb09lCGBx/rH5g2+R4B8EWrTHxBYwzRftho7CO4y9wtdtkPOJkaB5Ay26+8rGK1Zr8BP2IwExiaAAI97ErllIAxkh+ceUQU4S7y/knaLCr9vScsiPgfkL5oskajQ+kOfMRB6fuObOarYntiRDSzBBYuBLubfrMSCqn8= 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=eSOXk4B0; arc=none smtp.client-ip=209.85.210.198 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="eSOXk4B0" Received: by mail-pf1-f198.google.com with SMTP id d2e1a72fcca58-84e024d2129so4668691b3a.2 for ; Thu, 06 Aug 2026 16:36:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1786059411; x=1786664211; darn=vger.kernel.org; h=content-transfer-encoding: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=GbCVidvwQkuTYRlTXFKmfz6LBshlnXLBUNEqveo1L6E=; b=eSOXk4B09bZCFqZhXx/ZPuulmbDjWfK21C2oA2Y0W6NrDxiiIGZOAIMi0EBcXHoT8L wnxgW9heZaCz1exGIW+ehcAgi0UeGBNHiM+u7ysYIaU+VfNmBtd317M4b2IsNFdhHAaS KS0kmc2IglsxyQkredbefbgIpf6Sx3sJq+uZ9k28xzIKOQzhaEEIC5WfkZEllOVEqmPT M/RCyf0nkhaGNHzex/QuVM7d50M0PzI27EmxZLwn7ziLj655ByOa6iUkfk77PJpuwkip 0gRopjK8GfPvu4BgLQJ0zU35CfvVoQNlGmY3MZq9m8ly/SE7L+c9x15bffv8f038Ah4m Xhug== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786059411; x=1786664211; h=content-transfer-encoding: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=GbCVidvwQkuTYRlTXFKmfz6LBshlnXLBUNEqveo1L6E=; b=NhkPV6V/7ecQebVvKciimsn8t1FSi1k2wsAyybX1R+E5v2GznVX9PwkRGg06mQRlC0 esqpqeoPIYXbnO0aiL20LAiSa8d/V3pDc2EvTiLdG5yK6r97y6U9axIx9YV5eI3DgK3d grKfhmneNYKf1XLn7709bQHNJmqQtgkJNPGt/J+57u553y+zGeCRaJQ80eR9NyETkgIr JNOK3b0bUGXvLfPVa4URzYtf6U+bQLmv0VEejCqo3wZNuuhqAbEUL6J8xBkwD+lAkUDU 40P2pT4vX4BicwCWHcdnMxBpVeqYagQKUx8GBoQLIze01MPJcLyTMHmGYRyhpJPqxrd4 x6hA== X-Forwarded-Encrypted: i=1; AHgh+RrKnestloielRIc5JRZuSzgWb9TBGT6dPaLVTUNc5At+2cjth1F5cDSeMKRGQODv/LenoNbSBYzgDcaCys=@vger.kernel.org X-Gm-Message-State: AOJu0YwUi6bfEqfoBSSOKc+oBJ996xEuE6tBOJ6DzpIVMuAKqEZL+nBX 8uKHuVbOVcj2hAFING6i0o5HnYQ9NkIHGwDUYPrl5cnuDiym/fQk2uM6FIIGnvcVkZDKM1OSgTY xvajbGw== X-Received: from pfbll6.prod.google.com ([2002:a05:6a00:7286:b0:84e:a25:1e6b]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:3a12:b0:848:354f:4f8f with SMTP id d2e1a72fcca58-84f2dff3015mr20822585b3a.22.1786059410525; Thu, 06 Aug 2026 16:36:50 -0700 (PDT) Reply-To: Sean Christopherson Date: Thu, 6 Aug 2026 16:35:38 -0700 In-Reply-To: <20260806233609.212337-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260806233609.212337-1-seanjc@google.com> X-Mailer: git-send-email 2.55.0.679.g6767b8d81c-goog Message-ID: <20260806233609.212337-22-seanjc@google.com> Subject: [PATCH v6 21/51] x86/kvm: Obtain TSC frequency from PV CPUID if present From: Sean Christopherson To: Kiryl Shutsemau , Rick Edgecombe , Sean Christopherson , Paolo Bonzini , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Long Li , Ajay Kaher , Alexey Makhalov , Jan Kiszka , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Juergen Gross , Daniel Lezcano , Thomas Gleixner , John Stultz Cc: Vitaly Kuznetsov , Broadcom internal kernel review list , Boris Ostrovsky , Stephen Boyd , Miroslav Lichvar , x86@kernel.org, linux-coco@lists.linux.dev, kvm@vger.kernel.org, linux-hyperv@vger.kernel.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, Michael Kelley , Tom Lendacky , Nikunj A Dadhania , David Woodhouse , David Woodhouse , Thomas Gleixner Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable From: David Woodhouse In https://lkml.org/lkml/2008/10/1/246 a proposal was made for generic CPUID conventions across hypervisors. It was mostly shot down in flames, but the leaf at 0x40000010 containing timing information didn't die. It's used by XNU and FreeBSD guests under all hypervisors=C2=B9=C2=B2 to de= termine the TSC frequency, and also exposed by the EC2 Nitro hypervisor (as well as, presumably, VMware). FreeBSD's Bhyve is probably just about to start exposing it too. Use it under KVM to obtain the TSC frequency more accurately, instead of reverse-calculating the frequency from the mul/shift values in the KVM clock. Use the information to get the CPU frequency as well (kvmclock feeds in kvm_get_tsc_khz() for both TSC and CPU calibration), as the info from CPUID is superior in every way; whether or not kvmclock should be overriding CPU calibration in the first place is an entirely different question. Use the info from CPUID even if the user explicitly disables kvmclock, or if it's unsupported. The PV CPUID leaf has no dependency on kvmclock, and is in fact more useful if kvmclock is disabled since the kernel won't be able to use kvmclock to derive a derive the TSC frequency. Before: [ 0.000020] tsc: Detected 2900.014 MHz processor After: [ 0.000020] tsc: Detected 2900.015 MHz processor $ cpuid -1 -l 0x40000010 CPU: hypervisor generic timing information (0x40000010): TSC frequency (Hz) =3D 2900015 bus frequency (Hz) =3D 1000000 Note! *Independently* query for non-null get_{cpu,tsc}_khz() overrides so that kvmclock doesn't clobber x86_init.hyper.get_cpu_khz() if/when KVM adds support for getting the CPU frequency separately from the TSC frequency. =C2=B9 https://github.com/apple/darwin-xnu/blob/main/osfmk/i386/cpuid.c =C2=B2 https://github.com/freebsd/freebsd-src/commit/4a432614f68 Signed-off-by: David Woodhouse Co-developed-by: Sean Christopherson Signed-off-by: Sean Christopherson --- arch/x86/kernel/kvm.c | 33 +++++++++++++++++++++++++++++++++ arch/x86/kernel/kvmclock.c | 6 ++++-- 2 files changed, 37 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 5b554e480c0e..8ed02f4f5775 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -49,6 +49,8 @@ #include #include =20 +static unsigned int kvm_tsc_khz_cpuid __initdata; + DEFINE_STATIC_KEY_FALSE_RO(kvm_async_pf_enabled); =20 static int kvmapf =3D 1; @@ -913,6 +915,21 @@ bool kvm_para_available(void) } EXPORT_SYMBOL_GPL(kvm_para_available); =20 +static u32 __init kvm_cpuid_timing_info_leaf(void) +{ + u32 base =3D kvm_cpuid_base(); + + if (!base || cpuid_eax(base) < (base | KVM_CPUID_TIMING_INFO)) + return 0; + + return base | KVM_CPUID_TIMING_INFO; +} + +static unsigned int __init kvm_get_tsc_khz(void) +{ + return kvm_tsc_khz_cpuid; +} + unsigned int kvm_arch_para_features(void) { return cpuid_eax(kvm_cpuid_base() | KVM_CPUID_FEATURES); @@ -962,6 +979,7 @@ static void __init kvm_init_platform(void) .mask_lo =3D (u32)(~(SZ_4G - tolud - 1)) | MTRR_PHYSMASK_V, .mask_hi =3D (BIT_ULL(boot_cpu_data.x86_phys_bits) - 1) >> 32, }; + u32 timing_info_leaf; =20 if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT) && kvm_para_has_feature(KVM_FEATURE_MIGRATION_CONTROL)) { @@ -1009,6 +1027,21 @@ static void __init kvm_init_platform(void) wrmsrq(MSR_KVM_MIGRATION_CONTROL, KVM_MIGRATION_READY); } + + /* + * If KVM advertises the frequency directly in CPUID, use that instead + * of reverse-calculating it from the KVM clock data, or worse, trying + * to calibratate the TSC using an emulated device. + */ + timing_info_leaf =3D kvm_cpuid_timing_info_leaf(); + if (timing_info_leaf) { + kvm_tsc_khz_cpuid =3D cpuid_eax(timing_info_leaf); + if (kvm_tsc_khz_cpuid) { + x86_init.hyper.get_tsc_khz =3D kvm_get_tsc_khz; + x86_init.hyper.get_cpu_khz =3D kvm_get_tsc_khz; + } + } + kvmclock_init(); x86_platform.apic_post_init =3D kvm_apic_init; =20 diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c index 29ca37e9a3bc..f55d0305d1f3 100644 --- a/arch/x86/kernel/kvmclock.c +++ b/arch/x86/kernel/kvmclock.c @@ -342,8 +342,10 @@ void __init kvmclock_init(void) flags =3D pvclock_read_flags(&hv_clock_boot[0].pvti); kvm_sched_clock_init(flags & PVCLOCK_TSC_STABLE_BIT); =20 - x86_init.hyper.get_tsc_khz =3D kvmclock_get_tsc_khz; - x86_init.hyper.get_cpu_khz =3D kvmclock_get_tsc_khz; + if (!x86_init.hyper.get_tsc_khz) + x86_init.hyper.get_tsc_khz =3D kvmclock_get_tsc_khz; + if (!x86_init.hyper.get_cpu_khz) + x86_init.hyper.get_cpu_khz =3D kvmclock_get_tsc_khz; x86_platform.get_wallclock =3D kvm_get_wallclock; x86_platform.set_wallclock =3D kvm_set_wallclock; #ifdef CONFIG_X86_LOCAL_APIC --=20 2.55.0.679.g6767b8d81c-goog