linux-kernel - RE: [PATCH 03/16] KVM: x86: set gfn-to-pfn cache length consistently with VM word size

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Message-ID: <000fac2ae9394da6b51c2138c5816a45@amazon.co.uk>
Date:   Mon, 14 Nov 2022 11:27:44 +0000
From:   "Durrant, Paul" <pdurrant@...zon.co.uk>
To:     David Woodhouse <dwmw2@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mhal@...x.co" <mhal@...x.co>,
        "Kaya, Metin" <metikaya@...zon.co.uk>
Subject: RE: [PATCH 03/16] KVM: x86: set gfn-to-pfn cache length consistently with VM
 word size

> -----Original Message-----
> From: David Woodhouse <dwmw2@...radead.org>
> Sent: 13 November 2022 13:37
> To: Paolo Bonzini <pbonzini@...hat.com>; Sean Christopherson
> <seanjc@...gle.com>
> Cc: linux-kernel@...r.kernel.org; kvm@...r.kernel.org; mhal@...x.co;
> Durrant, Paul <pdurrant@...zon.co.uk>; Kaya, Metin <metikaya@...zon.co.uk>
> Subject: RE: [EXTERNAL][PATCH 03/16] KVM: x86: set gfn-to-pfn cache length
> consistently with VM word size
> 
> On Sun, 2022-11-13 at 13:32 +0000, David Woodhouse wrote:
> > For the runstate area, I think we can live with using a gfn_to_hva
> > cache instead, and writing via the userspace address (with appropriate
> > atomicity for the RUNSTATE_runnable case as we have at the moment
> > gating the refresh).
> 
> Which mostly involves just reverting commit a795cd43c5b5 I think?
> 
> IIRC the reason for that commit was mostly consistency with other
> things that really *did* want to be switched to gpc.

A straight reversion would re-introduce the page-spanning check in kvm_xen_vcpu_set_attr() but I think we can just leave that out.

  Paul