linux-kernel - Re: [PATCH v8 15/15] KVM: xen: allow vcpu

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Message-ID: <40d2e3051fbc70308cf0b6fc5298b65bf5737012.camel@infradead.org>
Date:   Wed, 22 Nov 2023 11:25:47 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     paul@....org, Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 15/15] KVM: xen: allow vcpu_info content to be
 'safely' copied

On Wed, 2023-11-22 at 10:55 +0000, Paul Durrant wrote:
> 
> > > Wait, didn't we realise that this leaves the bits set in the shadow
> > > evtchn_pending_sel that get lost on migration?
> > > 
> 
> Indeed we did not, but that's not something that *this* patch, or even 
> this series, is dealing with.  We also know that setting the 'width' of 
> shared_info has some issues, but again, can we keep that for other 
> patches? The series is at v9 and has already suffered a fair amount of 
> scope-creep.

Hrm... OK, that makes sense. This series is attempting to address the
fact that we can't do overlays on memslots without temporarily taking
away GPA ranges that we didn't mean to change. This patch is sufficient
to allow evtchn delivery to work while the memslots are being frobbed,
because userspace takes the vcpu_info away during the update.

In that case the shadow works just fine.

So yeah, if you want to handle the migration case separately then that
seems reasonable.

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