From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 CD19A35F18B for ; Sat, 12 Sep 2026 05:53:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789192384; cv=none; b=rfaV4V8FxcnCv6pcr/Fi1iLRRr2SjhBSWAP9OuqCylkmJWgXxPB5yVMDRrNk/In1VAtcVynU1hGEzE6wqCOQZ08DIcYMCphvXUz+YBNBk7GIVxNYY7PBESMUwkHZly+VIoI6eeNTW/wii/K8+KgtdPEEABk0EKvJXDslPn9THwQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789192384; c=relaxed/simple; bh=Vdsd0+liAiYVOiW+hrdEdgsiU3r9OsVIG2puvFA6Ptg=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=SMj6YC4SP6HKjWPcMWgtPdXcVtgGnbdthI1i6UDP/3i75QhFCdo1bJ1Ua25vwN0R+dKg98gt85c4uY1pVUv1+dDSAQQPXc/oMtBzZdkps31UvmPWCnLbNrLJabcWyi5OXic+igBkeeo2nuID4QsG7+qQrV5tcZ/DPNqY5DMQNo0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=A2FqoytX; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="A2FqoytX" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1789192379; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=UgljSemThQOtOsTysjE4U+NLvcvT+dhG3CA8+WOGtRY=; b=A2FqoytXC15b9Fos44Ek2mlS1UBYJiAW+Vq4y1fLGFIs2E5+5i8r4pqJQwIbD3EP4Ldzm0 gaWmVQE7vyBerf1AgRibRPNSyBu9yiHWE1EgEdGQWt06zEEh593dRPWFdyHBDLATcVB4Up 3OPGocaerfYnyCWhDoaCJTq25kmJ5x8= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-647-4VR2GVmnOWelIIfDhX0nRA-1; Sat, 12 Sep 2026 01:52:52 -0400 X-MC-Unique: 4VR2GVmnOWelIIfDhX0nRA-1 X-Mimecast-MFC-AGG-ID: 4VR2GVmnOWelIIfDhX0nRA_1789192366 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 864C91954B11; Sat, 12 Sep 2026 05:52:46 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.5]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 683AA1800345; Sat, 12 Sep 2026 05:52:45 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 122C821E6A04; Sat, 12 Sep 2026 07:52:43 +0200 (CEST) From: Markus Armbruster To: Michael Roth Cc: , , , , , , , , , , , Subject: Re: [PATCH v2 07/19] accel/kvm: Add CGS option to control in-place conversion support In-Reply-To: (Michael Roth's message of "Fri, 11 Sep 2026 12:22:45 -0500") References: <20260908205236.838281-1-michael.roth@amd.com> <20260908205236.838281-8-michael.roth@amd.com> <878q5bosi3.fsf@pond.sub.org> Date: Sat, 12 Sep 2026 07:52:43 +0200 Message-ID: <87pkyj3tjo.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Michael Roth writes: > On Wed, Sep 09, 2026 at 08:20:36AM +0200, Markus Armbruster wrote: >> Michael Roth writes: >> >> > For confidential guests, guest_memfd is currently used only for private >> > guest memory, and normal guest memory comes from the configured memory >> > backend just as it does for a non-confidential guest. It is now possible >> > to use the same physical memory to back a particular GPA regardless of >> > whether it is in a shared or private state. This avoids the need to >> > rely on discarding memory between shared/private conversions (to avoid >> > doubled memory usage), and is intended to be the primary mode of using >> > guest_memfd for confidential guests moving forward, and future features >> > like hugepage support will likely require it. >> > >> > Add an option to enable this support. Since ConfidentialGuestSupport is >> > already used to track some guest_memfd-related functionality (e.g. >> > whether it is required for the configured machine), similarly introduce >> > this option as a property of ConfidentialGuestSupport. >> > >> > Also add the KVM-specific checks to enable this support, but leave the >> > option disabled until other required changes are implemented for >> > CGS variants that intend to make use of KVM's in-place conversion >> > support. >> > >> > While technically the convert-in-place option could be introduced as an >> > SEV-specific option, it is a given that TDX will also be introducing >> > in-place conversion support based on the same guest_memfd kernel >> > infrastructure, so introduce it via a new >> > ConfidentialGuestSupportProperties base class that other confidential VM >> > implementations can utilized for common options. >> > >> > Signed-off-by: Michael Roth >> >> [...] >> >> > diff --git a/qapi/qom.json b/qapi/qom.json >> > index 909add4299..20d6fefb04 100644 >> > --- a/qapi/qom.json >> > +++ b/qapi/qom.json >> > @@ -1005,6 +1005,21 @@ >> > 'if': 'CONFIG_IGVM', >> > 'data': { 'file': 'str' } } >> > >> > +## >> > +# @ConfidentialGuestSupportProperties: >> > +# >> > +# Properties for ConfidentialGuestSupport base class. >> > +# >> > +# @convert-in-place: If true, the same physical pages are reused >> > +# when memory is converted between shared and private states. >> > +# If false (default), separate allocations are used depending >> > +# on whether the page is private or shared. >> >> Any guidance on when to enable @convert-in-place? > > A lot of it boils down to more Confidential Compute architectures > now requiring it for new features (hugepage support and SEV-TIO will > require it for instance). convert-in-place=true maps more closely to > a normal VM, and not having more complicated memory management > requirements avoids additional complications up the stack (like > accounting for instances where memory usage might balloon passed > expected resource limits due to needing to management multiple > memory allocations for a given GPA range). > > convert-in-place=false will likely become a legacy path unless other > use-case arise, but they'd probably need to be super-duper useful > to warrant enabling new things on top of it going forward. What are the use cases for false *now*? Can a change from false to true upset a guest? > I'll try to work something along that line into the guest-memfd.rst > I proposed for Peter's series and add/reference that as part of this > patch. > >> >> > +# >> > +# Since: 11.2 >> > +## >> > +{ 'struct': 'ConfidentialGuestSupportProperties', >> > + 'data': { '*convert-in-place': 'bool' } } >> > + >> > ## >> > # @SevCommonProperties: >> > # [...]