From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f202.google.com (mail-pl1-f202.google.com [209.85.214.202]) (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 211FD3FC5D3 for ; Fri, 29 May 2026 14:45:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780065914; cv=none; b=ucVG0Cz4ExrIyRcdzhSzWvrUV6A63U4HsB4ANR/t5Y6S2jCGXVVQpmtjoMe7BbIaNvipAQIKguvKQNfC8nOnt1DfFf+9hLpDgNGRtVfGPsQr5cpv8p2fUPdOtdMxxnv3UXGp+L/zXGhOenVns9ftJFThOGpAhnMJaxVrHWvb16k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780065914; c=relaxed/simple; bh=367+/Zpr6KHk7eYYDaXSVUgo5iAHZwFbHGvXpB65Nmw=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=aFS04Hff8+YJ9eyTWYvjIHo9ClbEt++/DCvVWiwToW4uNywCFtKvkwkQ1XrKHNrC95on/MxfBCFNq5LtSurpeU2SjO4I1HIudQ/w7GR3AU5j8gNToySklFlIWFYliU1vTdmbAk7GDVPdxhjMCftO8TYuG07mV8IbbAa2obaYssg= 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=t0MNStYO; arc=none smtp.client-ip=209.85.214.202 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="t0MNStYO" Received: by mail-pl1-f202.google.com with SMTP id d9443c01a7336-2bf30576aa3so2122455ad.3 for ; Fri, 29 May 2026 07:45:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1780065911; x=1780670711; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:reply-to:from:to:cc:subject:date :message-id:reply-to; bh=FoqgLgRaMBwMlzlRb5ZdKmNASLSl22kGdknpkiNEuDA=; b=t0MNStYOFi6pd8H6B3F0StVdV68M8/rV+cumiWC1Bs2oN6gXcgUzUCHT0VWjKAi7t+ CHwNWWH0qkdyv0tLtZzW8iSTolwJlDS93NMoEu6sD3Zb7f3vTL7H4dTHkHdLvCHGP12m 3wGK8EWSpmJNhakcIOd+YEQ6bl0G5B84Az6wNyA/lkyzqkQjdmRTUl1fgS97bQwNFhWp CDSKdm8VO7FWvL/y8d+UC+2UEbGWqVaCfseYJ7k+2wIrFB3sy0+R2w1sBrfz3aNzOutb 9i6V7K2JzEU5Cdv+UEqoV2fwJy29pvpz0gni95EVqS4Z9ffpq2da1D+jvvNQhFmKwFSG smJA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1780065911; x=1780670711; h=content-transfer-encoding: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; bh=FoqgLgRaMBwMlzlRb5ZdKmNASLSl22kGdknpkiNEuDA=; b=mHqX3W/NyDLYN9Nd52l3kHxgktX25+vY0F6uZm8+XgffmYUN5dNPOviCAd3d75ECOj jOCqlVC/syKTupwyYM4H/Od1NwtTD2JVIlHQDQilPdBHywArspaD4reN51zwSash7ViK 3ycxl1qj2laJoC5L7zPp1Rx0gWBcvf6iSvMshHIGDGBRUBMoGPJfjxqXw2zjJBcDmVt+ AyTLuY6g6N/Xx9P2TX666TeughojCN+/5bbKoln19dtnX6F6wyy8q7Wuo8zacxnuRyLf 0pkWMh2E4Fv2eB+N/ST2MJAl9Il/X6XmPAlTUKes4IuMu5Xq/Xy09OVjSDIyJyEO20Yz rOmw== X-Forwarded-Encrypted: i=1; AFNElJ9G9AqaCNZWBA3YFUXyZbarduSJCHuAxQDvpoWJloUh6iaWau5xjELYZ18oZ30Ho3+84xdHywrgJZZ/mps=@vger.kernel.org X-Gm-Message-State: AOJu0YzQlxLpqD89p73KxkaUzoVNYScWiGdzqWbCZ3JKaXirYz1565Bs V0yHaU+ofvUHnrebZOIAEwsYRNtW62c7icbkbfpL3BcZ0dP9Da9RYuG9XF7pysdDHna7qLTuRtC D7HuYUA== X-Received: from plbjh24.prod.google.com ([2002:a17:903:3298:b0:2bf:14c9:866d]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:d4c2:b0:2bf:2589:7bc2 with SMTP id d9443c01a7336-2bf367d3ab7mr1162735ad.15.1780065910985; Fri, 29 May 2026 07:45:10 -0700 (PDT) Reply-To: Sean Christopherson Date: Fri, 29 May 2026 07:44:03 -0700 In-Reply-To: <20260529144435.704127-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260529144435.704127-1-seanjc@google.com> X-Mailer: git-send-email 2.54.0.823.g6e5bcc1fc9-goog Message-ID: <20260529144435.704127-17-seanjc@google.com> Subject: [PATCH v4 16/47] x86/kvm: Obtain TSC frequency from PV CPUID if present From: Sean Christopherson To: Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Kiryl Shutsemau , Sean Christopherson , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Long Li , Ajay Kaher , Alexey Makhalov , Jan Kiszka , Andy Lutomirski , Peter Zijlstra , Juergen Gross , Daniel Lezcano , John Stultz Cc: "H. Peter Anvin" , Rick Edgecombe , Vitaly Kuznetsov , Broadcom internal kernel review list , Boris Ostrovsky , Stephen Boyd , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, linux-hyperv@vger.kernel.org, virtualization@lists.linux.dev, xen-devel@lists.xenproject.org, David Woodhouse , Tom Lendacky , Nikunj A Dadhania , David Woodhouse , Michael Kelley , 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 dcef84da304b..909d3e5e5bcd 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; @@ -911,6 +913,21 @@ 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); @@ -960,6 +977,7 @@ 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)) { @@ -1007,6 +1025,21 @@ 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 c4a782a0c903..404f60741aa8 100644 --- a/arch/x86/kernel/kvmclock.c +++ b/arch/x86/kernel/kvmclock.c @@ -320,8 +320,10 @@ 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 2.54.0.823.g6e5bcc1fc9-goog