linux-kernel - Re: [PATCH v4] KVM: x86/xen: Update Xen CPUID Leaf 4 (tsc info) sub-leaves, if present

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Date:   Mon, 27 Jun 2022 15:19:15 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paul Durrant <pdurrant@...zon.com>
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Woodhouse <dwmw2@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v4] KVM: x86/xen: Update Xen CPUID Leaf 4 (tsc info)
 sub-leaves, if present

On Wed, Jun 22, 2022, Paul Durrant wrote:
> The scaling information in subleaf 1 should match the values set by KVM in
> the 'vcpu_info' sub-structure 'time_info' (a.k.a. pvclock_vcpu_time_info)
> which is shared with the guest, but is not directly available to the VMM.
> The offset values are not set since a TSC offset is already applied.
> The TSC frequency should also be set in sub-leaf 2.
> 
> Cache pointers to the sub-leaves when CPUID is updated by the VMM and
> populate the relevant information prior to entering the guest.

All of my comments about the code still apply.

https://lore.kernel.org/all/YrMqtHzNSean+qkh@google.com

> Signed-off-by: Paul Durrant <pdurrant@...zon.com>
> ---
> Cc: David Woodhouse <dwmw2@...radead.org>

Cc: can go in the changelog, it's helpful info to carry with the commit as it
documents who was made aware of the patch, e.g. show who may have had a cance to
object/review.

> 
> v2:
>  - Make sure sub-leaf pointers are NULLed if the time leaf is removed
> 
> v3:
>  - Add leaf limit check in kvm_xen_set_cpuid()
> 
> v4:
>  - Update commit comment

Please start with the most recent verison and work backardwards, that way reviewers
can quickly see the delta for _this_ version.  I.e.


v4:

v3:

v2:

v1: