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Re: [PATCH v3 32/41] x86/tsc: Rejects attempts to override TSC calibration with lesser routine
- To: Sean Christopherson <seanjc@xxxxxxxxxx>, Kiryl Shutsemau <kas@xxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>, Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>, Wei Liu <wei.liu@xxxxxxxxxx>, Dexuan Cui <decui@xxxxxxxxxxxxx>, Long Li <longli@xxxxxxxxxxxxx>, Ajay Kaher <ajay.kaher@xxxxxxxxxxxx>, Alexey Makhalov <alexey.makhalov@xxxxxxxxxxxx>, Jan Kiszka <jan.kiszka@xxxxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxx>, John Stultz <jstultz@xxxxxxxxxx>
- From: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
- Date: Thu, 21 May 2026 00:50:38 +0100
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- Cc: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>, Broadcom internal kernel review list <bcm-kernel-feedback-list@xxxxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Stephen Boyd <sboyd@xxxxxxxxxx>, x86@xxxxxxxxxx, linux-coco@xxxxxxxxxxxxxxx, kvm@xxxxxxxxxxxxxxx, linux-hyperv@xxxxxxxxxxxxxxx, virtualization@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, Michael Kelley <mhklinux@xxxxxxxxxxx>, Tom Lendacky <thomas.lendacky@xxxxxxx>, Nikunj A Dadhania <nikunj@xxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>
- Delivery-date: Wed, 20 May 2026 23:50:50 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Fri, 2026-05-15 at 12:19 -0700, Sean Christopherson wrote:
> When registering a TSC frequency calibration routine, sanity check that
> the incoming routine is as robust as the outgoing routine, and reject the
> incoming routine if the sanity check fails.
>
> Because native calibration routines only mark the TSC frequency as known
> and reliable when they actually run, the effective progression of
> capabilities is: None (native) => Known and maybe Reliable (PV) =>
> Known and Reliable (CoCo). Violating that progression for a PV override
> is relatively benign, but messing up the progression when CoCo is
> involved is more problematic, as it likely means a trusted source of
> information (hardware/firmware) is being discarded in favor of a less
> trusted source (hypervisor).
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
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