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 15:23:54 +0000
From:   "Durrant, Paul" <pdurrant@...zon.co.uk>
To:     Sean Christopherson <seanjc@...gle.com>
CC:     "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...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

> -----Original Message-----
> From: Sean Christopherson <seanjc@...gle.com>
> Sent: 27 June 2022 16:19
> To: Durrant, Paul <pdurrant@...zon.co.uk>
> 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: [EXTERNAL][PATCH v4] KVM: x86/xen: Update Xen CPUID Leaf 4 (tsc info) sub-leaves, if
> present
> 
> CAUTION: This email originated from outside of the organization. Do not click links or open
> attachments unless you can confirm the sender and know the content is safe.
> 
> 
> 
> 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
> 

Apologies. Not sure how I missed them; I'll send a response shortly.

> > 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:

Ok.

  Paul