linux-kernel - Re: [PATCH RFC v7 52/64] KVM: SVM: Provide support for SNP_GUEST

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Date:   Thu, 11 May 2023 16:32:58 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Dionna Amalie Glaze <dionnaglaze@...gle.com>
Cc:     Tom Lendacky <thomas.lendacky@....com>,
        Alexey Kardashevskiy <aik@....com>,
        Ashish Kalra <ashish.kalra@....com>,
        Michael Roth <michael.roth@....com>, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, hpa@...or.com, ardb@...nel.org,
        pbonzini@...hat.com, vkuznets@...hat.com, wanpengli@...cent.com,
        jmattson@...gle.com, luto@...nel.org, dave.hansen@...ux.intel.com,
        slp@...hat.com, pgonda@...gle.com, peterz@...radead.org,
        srinivas.pandruvada@...ux.intel.com, rientjes@...gle.com,
        dovmurik@...ux.ibm.com, tobin@....com, bp@...en8.de,
        vbabka@...e.cz, kirill@...temov.name, ak@...ux.intel.com,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
        dgilbert@...hat.com, jarkko@...nel.org, harald@...fian.com,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH RFC v7 52/64] KVM: SVM: Provide support for
 SNP_GUEST_REQUEST NAE event

On Thu, May 11, 2023, Dionna Amalie Glaze wrote:
> Would it be okay to request that we add a KVM stat for how often there
> are GUEST_REQUEST_NAE exits? I think it'd be good for service
> operators to get a better idea how valued the feature is.

Heh, it's always ok to request something, but sometimes the answer will be no.

And in the case, the answer is likely "no stat for you".  A year or so ago, in the
context of us (Google) trying to upstream a pile of stats, we (KVM folks) came to
a rough consensus that KVM should only add upstream stats if they are relatively
generic and (almost) universally useful[*].  IMO, a one-off stat for a specific exit
reason is too narrowly focused, e.g. collecting information on all exit reasons is
superior.  And no, that won't be accepted upstream either, because for some environments
gathering detailed information on all exits is too much overhead (also covered in
the link).

FWIW, we (GCE) plan on carrying stats like this in out-of-tree patches, i.e. your
request for stats is likely something that would get accepted internally (if it
isn't already captured through our generic stats collection).

[*] https://lore.kernel.org/all/87czp0voqg.wl-maz@kernel.org