From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 C7B7830F7F3; Mon, 6 Apr 2026 05:37:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775453853; cv=none; b=YsJ0/nh6tRt9nwsAsQTfpNudEb9trCTJ7GCPEXXEm6SA5GrgiOZsnARqFz/ouq62qhENL3zW6seFGEnzx8sNyy7eD4iE5/3OkLZvWd2WrEEZtuPqVgGfL3K7YUjbmP2sgCdFaRnGnKngHfqJh+7XsWEJ2ogxaNow2bnK5tItxyg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775453853; c=relaxed/simple; bh=3H7RsowI2ljlCeNQo2yEaOqoIoLG6qEMEjbd4gFPCAk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=G4JJLfOUsCBn/rKIkErsNNwDcS9gOMwXkIYNxz3JFWbQhJ9q7qzl+tPBY6DadvEcKG7l1Q4fximjqdW40aSh3OEyUfZWGo8gX3orrSrQMUOLXo+LjEn1GjYQEtU6koT8XnI1hFYHj94EbmJKMwmh3mHHp+SUvhG+pCNZy85BCFE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=4Q97rkte; arc=none smtp.client-ip=198.137.202.133 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=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="4Q97rkte" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=pbhmUnBc+LFMvDuylockDJOhrvEN4yYtm4qtLcRwpFA=; b=4Q97rkteH2M8VqUr9K7iJpDsKi 8Yc//EWBPDpGzC15+FA6pjKLjYcYgYAv3M1hlnq8Df3Orza0UTQli1WcXhDtpOVEUis/Z8z4JLdqL kQNx/Dm2cC1q3RDWJ82c38FLRVG47eV+JmsW02NJmsVDufq0y/+9Q2MY8KdTq1OkHUahut707fLr5 k2QW4yJ4BF/s+HhC+pAyZc95zVJwT7lszndPATL9qgZCs1RuhINKSDu2CT5+f8Rbe9wGV8zWnmjNg K6Vd9N+UzCQYIJyoFg0lhP5UGSE9MUQ2hSr1jPsain2hreScZP1W2UHcDnnSfvbA4HWarUMm0JBF6 mVRLKwOw==; Received: from hch by bombadil.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1w9ceP-00000004oY7-0koH; Mon, 06 Apr 2026 05:37:29 +0000 Date: Sun, 5 Apr 2026 22:37:29 -0700 From: Christoph Hellwig To: Janosch Frank Cc: Christoph Hellwig , Eric Farman , Christian Borntraeger , Hendrik Brueckner , Claudio Imbrenda , David Hildenbrand , Paolo Bonzini , Jonathan Corbet , Shuah Khan , kvm@vger.kernel.org, linux-s390@vger.kernel.org Subject: Re: [PATCH v1 0/4] KVM: s390: Permit ESA mode guests in VSIE Message-ID: References: <20260401020915.1339228-1-farman@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html On Wed, Apr 01, 2026 at 12:00:59PM +0200, Janosch Frank wrote: > KVM is the latest hypervisor in a long list on s390. As such we implemented > the newest architecture as our starting point and only architecture > (zArch/64bit). > > There are others which don't start their guests from zArch mode but start > them in ESA and slowly move them through modes until they reach zArch. Those > other hypervisors often implement emulation for features and devices that > KVM doesn't support so there's some demand for using them. > > Why do we nest those hypervisors under KVM? We have products that work with > the KVM API so it's easier to nest than to re-write the product to use other > hypervisors in the first place. Makes sense. Maybe mention this in the cover letter, and also that you're not looking into full device model support for older systems?