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From: Paolo Bonzini <pbonzini@redhat.com>
Date: Mon, 22 Apr 2024 14:22:54 +0200
Message-ID: <CABgObfa0j34iEh81hhd7-t7ZM1GKAsvJb5xP6EoD2-c-8TnPqQ@mail.gmail.com>
Subject: Re: [PATCH 02/10] KVM: x86: Improve accuracy of KVM clock when TSC
 scaling is in force
To: David Woodhouse <dwmw2@infradead.org>
Cc: kvm@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>, 
	Sean Christopherson <seanjc@google.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, 
	Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org, 
	"H. Peter Anvin" <hpa@zytor.com>, Paul Durrant <paul@xen.org>, Shuah Khan <shuah@kernel.org>, 
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-kselftest@vger.kernel.org, Oliver Upton <oliver.upton@linux.dev>, 
	Marcelo Tosatti <mtosatti@redhat.com>, jalliste@amazon.co.uk, sveith@amazon.de
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On Thu, Apr 18, 2024 at 9:51=E2=80=AFPM David Woodhouse <dwmw2@infradead.or=
g> wrote:
>         gpa_t time;
>         struct pvclock_vcpu_time_info hv_clock;
> -       unsigned int hw_tsc_khz;
> +       unsigned int hw_tsc_hz;

Why not change this to u64? 4.3 GHz is scarily close to current
processors, though I expect that it will break a lot more software
than just KVM.

>  static int kvm_guest_time_update(struct kvm_vcpu *v)
>  {
> -       unsigned long flags, tgt_tsc_khz;
> +       unsigned long flags;
> +       uint64_t tgt_tsc_hz;

.. especially considering that you did use a 64-bit integer here
(though---please use u64 not uint64_t; and BTW if you want to add a
patch to change kvm_get_time_scale() to u64, please do.

Thanks,

Paolo