linux-kernel - Re: [PATCH v7 00/11] KVM: xen: update shared_info and vcpu

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Message-ID: <b7d0c879-3c44-4f44-b796-78c0d3855976@xen.org>
Date:   Thu, 9 Nov 2023 10:06:40 +0000
From:   Paul Durrant <xadimgnik@...il.com>
To:     David Woodhouse <dwmw2@...radead.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Paul Durrant <pdurrant@...zon.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org
Subject: Re: [PATCH v7 00/11] KVM: xen: update shared_info and vcpu_info
 handling

On 09/11/2023 10:02, David Woodhouse wrote:
> On Thu, 2023-10-05 at 09:36 +0100, Paul Durrant wrote:
>> On 05/10/2023 07:41, David Woodhouse wrote:
>>> On Mon, 2023-10-02 at 09:57 +0000, Paul Durrant wrote:
>>>> From: Paul Durrant <pdurrant@...zon.com>
>>>>
>>>> The following text from the original cover letter still serves as an
>>>> introduction to the series:
>>>>
>>>> "Currently we treat the shared_info page as guest memory and the VMM
>>>> informs KVM of its location using a GFN. However it is not guest memory as
>>>> such; it's an overlay page. So we pointlessly invalidate and re-cache a
>>>> mapping to the *same page* of memory every time the guest requests that
>>>> shared_info be mapped into its address space. Let's avoid doing that by
>>>> modifying the pfncache code to allow activation using a fixed userspace HVA
>>>> as well as a GPA."
>>>>
>>>> This version of the series is functionally the same as version 6. I have
>>>> simply added David Woodhouse's R-b to patch 11 to indicate that he has
>>>> now fully reviewed the series.
>>>
>>> Thanks. I believe Sean is probably waiting for us to stop going back
>>> and forth, and for the dust to settle. So for the record: I think I'm
>>> done heckling and this is ready to go in.
>>>
>>> Are you doing the QEMU patches or am I?
>>>
>>
>> I'll do the QEMU changes, once the patches hit kvm/next.
> 
> Note that I disabled migration support in QEMU for emulated Xen
> guests. You might want that for testing, since the reason for this work
> is to enable pause/serialize workflows.
> 
> Migration does work all the way up to XenStore itself, and
> https://gitlab.com/qemu-project/qemu/-/commit/766804b101d *was* tested
> with migration enabled. There are also unit tests for XenStore
> serialize/deserialize.
> 
> I disabled it because the PV backends on the XenBus don't have
> suspend/resume support. But a guest using other emulated net/disk
> devices should still be able to suspend/resume OK if we just remove the
> 'unmigratable' flag from xen_xenstore, I believe.

Ok. Enabling suspend/resume for backends really ought not to be that 
hard. The main reason for this series was to enable pause 
for-for-memory-reconfiguration but I can look into 
suspend/resume/migrate once I've done the necessary re-work.