From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 69A773E00BD; Tue, 19 May 2026 10:41:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779187297; cv=none; b=hwVp1TFkb54OzN0WTYWvstgEEj3WOJ8IxKaNlgVEpH0LE/UVEtpwu1L+arGL3IdqB678gLjpEAICT1A2w0BO2h+/fTykx5br6//ovXXyTpoBOZC6/WI9S/8k0yg2oGvF/B4i+ns8UwJk55yHrOBOd6g7IH7dlVLjqCt77dv6a+Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779187297; c=relaxed/simple; bh=FTeLEJ+DBjyBA74en4sSbr/tA7gdfdq14UWkB81djkA=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=acNsOLWA1minQNcsAV1XoU5yfX56pGCo31/ZMH9Ma/0+BB1DB756bHeXBIa5m6Xd43jyEz293YOuTh1LgOzZxbpMMbMemNaRHgdHF1KApaF6fKJlJeXBKDHHqZeAv6wQWCi6xOYm97QHNSWZdlvAsY+5Z0zKRjIcqc+srVY4T/I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=casper.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=PjJdwhZC; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=casper.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="PjJdwhZC" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=XgxjqnbsnE/azX8wgjK7JsLcG4H3KJRSlNZg2/kJsN8=; b=PjJdwhZCfZG6UrLoRGBgMsTBw0 uq0mxv++Qo1dzXWmuKdTMUpeVzJ0S3h4uxKoupYzO5IxliblCeUagVi8z+BXZP3Vrfar8mGCMoaAw N8NX8ESrjS5WRFgcHQo21xmraC/a/3wphPpdN2Juu9cIkGlR66ekTiZb1aT37tT0wmNgjbaymO8jS POtFTC5Olln8ohdlRsNGnFIXQOE02KkskUDmtDLJP69jWEGYXP9pUhQMirVfFfiPah/nO5ot366OD oKVkmxp/5+2t8ChU4MrYbmBoZbhaySF88QSOS9i/rGBlkDIugz59rTdmjCk8CW4T6ySndJj4kjlz2 hCUKmOPw==; Received: from 54-240-197-233.amazon.com ([54.240.197.233] helo=u09cd745991455d.ant.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wPHtA-00000005oCo-2Vn3; Tue, 19 May 2026 10:41:28 +0000 Message-ID: <3f9d731c3d26b0367600f1069e6425099bc34eac.camel@infradead.org> Subject: Re: [PATCH] Documentation: KVM: Document guest-visible compatibility expectations From: David Woodhouse To: Paolo Bonzini Cc: Marc Zyngier , Jonathan Corbet , Shuah Khan , kvm , Linux Doc Mailing List , "Kernel Mailing List, Linux" , Sean Christopherson , Jim Mattson , Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Raghavendra Rao Ananta , Eric Auger , Kees Cook , Arnd Bergmann , Nathan Chancellor , linux-arm-kernel , kvmarm@lists.linux.dev, linux-kselftest Date: Tue, 19 May 2026 11:41:26 +0100 In-Reply-To: References: <6856b269d2af706eae397e0cf9c1231f89d9a932.camel@infradead.org> <6afc4b95-3c15-4d71-877d-19b84e91ce05@redhat.com> <57bc082f4824d6114d3156744c25986effc29aca.camel@infradead.org> <86h5obya2r.wl-maz@kernel.org> <48b06e5655d56ff6eda30e563b34894fa0eb2f07.camel@infradead.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-GXcp10WwKY3OAbs7DkMA" User-Agent: Evolution 3.52.3-0ubuntu1.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html --=-GXcp10WwKY3OAbs7DkMA Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2026-05-13 at 18:24 +0200, Paolo Bonzini wrote: >=20 > > See commit https://git.kernel.org/torvalds/c/49a1a2c70a7f=C2=A0which ad= ds a > > new guest-visible feature in revision 3, but allowed userspace to > > restore the old behaviour by setting it to revision 2. All my patch > > above does, is make it possible to set it to revision 1 as > > well. Because https://git.kernel.org/torvalds/c/d53c2c29ae0d=C2=A0previ= ously > > changed the behaviour and bumped the default to 2 *without* allowing > > userspace to restore the prior behaviour, and we've been carrying a > > *revert* of that patch. > >=20 > > Why would we *not* accept such a patch? >=20 > Agreed. Even ignoring your revert, there's no reason why any upgrade > past 49a1a2c70a7f has to be from after d53c2c29ae0d. So where do we go from here? I assume you'll be taking this Documentation patch via the KVM tree? But what about the actual fix at=20 https://lore.kernel.org/all/20260511113558.3325004-2-dwmw2@infradead.org/ This is a simple and unintrusive bug fix to make KVM/arm64 follow the "common sense" requirement that the doc patch codifies, apparently being rejected with the rather bizarre claim that KVM has no *need* to maintain guest-visible compatibility across host kernel changes. So... what next? Is one of the other KVM/arm64 maintainers going to speak up? Paolo would you consider taking the fixes through your tree directly?=20 Does Arm not actually *care* whether AArch64 is considered a stable and mature platform for KVM hosting? We don't have CONFIG_EXPERIMENTAL any more, do we? Or perhaps we could mark it such. 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