linux-kernel - Re: [PATCH v2 11/12] KVM: selftests / xen: don't explicitly set the vcpu

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Message-ID: <425F7A5D-58D1-4D94-A88C-E7B1EAEAD084@infradead.org>
Date:   Mon, 18 Sep 2023 15:05:39 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     paul@....org, Paul Durrant <xadimgnik@...il.com>,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
CC:     Paul Durrant <pdurrant@...zon.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v2 11/12] KVM: selftests / xen: don't explicitly set the vcpu_info address

On 18 September 2023 14:41:08 BST, Paul Durrant <xadimgnik@...il.com> wrote:
>Well, if the VMM is using the default then it can't unmap it. But setting a vcpu_info *after* enabling any event channels would be a very odd thing for a guest to do and IMO it gets to keep the pieces if it does so.

Hm, I suppose I'm OK with that approach. The fact that both VMM implementations using this KVM/Xen support let the guest keep precisely those pieces is a testament to that :)

But now we're hard-coding the behaviour in the kernel and declaring that no VMM will be *able* to "fix" that case even if it does want to. So perhaps it wants a modicum more thought and at least some explicit documentation to that effect?

And a hand-wavy plan at least for what we'd do if we suddenly did find a reason to care?