From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta1.migadu.com (out-178.mta1.migadu.com [95.215.58.178]) (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 D85F31A08D1 for ; Thu, 19 Dec 2024 17:36:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734629793; cv=none; b=YTA7miJyuOHEH8JffzvYcVlxHztAtfTHbkewluDzCb6J8oQstWEt0eS0ywwfOLgobKOjh1UN4LNlpfxi3vFw13/ni6qv46zkVUS4kVempkTqCAEP8SV83pITgCJXPAGssJG6VpsBE6RLpVBPXdSxV7sEXqr16fqe1ggtYcnGJI8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734629793; c=relaxed/simple; bh=vXVCpNIHhh8sPsdymXXaKIvYSf2FwYaG6DsEdj3/nu0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ItRIntRXCY/kwbqbX8zFqV9AUJ1dqbP+dJ8Y2hlawXlOvKD9ThUl/29pO2PfAVpSqoDU1237+3PcsJWjqBZwsoVH13dYqdoBTlILVNUvbrbulT44znxv10153oujtDTPHDM192Yp7K5OeCXVvWQV5ZFE6BsF0B8k8M7bLzWDnMI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=Csc+vQ+W; arc=none smtp.client-ip=95.215.58.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="Csc+vQ+W" Date: Thu, 19 Dec 2024 09:36:16 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1734629788; 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=Ap48egQQYjTFlsWXbHaljCMT9L0YYN5hLo9udbi2yJE=; b=Csc+vQ+WRhHRGl7OlGJx22m1D4aOa0/LrTi+9UzU81TvkO0x8LP2EFgVOoV+/aJvDIr5Bx lzikpMxhvRNERHpxOgGQDhye/T8UhGy7Crt3bQagdyQGlb53vpJGxPaoWSWNjjWqwilWVC DlVPRbzgEoEaUrY0b/iu0jNpvJ/pDDQ= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Oliver Upton To: Marc Zyngier Cc: Shameer Kolothum , kvmarm@lists.linux.dev, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, cohuck@redhat.com, eric.auger@redhat.com, sebott@redhat.com, yuzenghui@huawei.com, wangzhou1@hisilicon.com, jiangkunkun@huawei.com, jonathan.cameron@huawei.com, anthony.jebson@huawei.com, linux-arm-kernel@lists.infradead.org, linuxarm@huawei.com Subject: Re: [PATCH v4 0/3] KVM: arm64: Errata management for VM Live migration Message-ID: References: <20241218105345.73472-1-shameerali.kolothum.thodi@huawei.com> <86a5csq93o.wl-maz@kernel.org> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <86a5csq93o.wl-maz@kernel.org> X-Migadu-Flow: FLOW_OUT On Thu, Dec 19, 2024 at 10:07:39AM +0000, Marc Zyngier wrote: > Hi Shameer, > > On Wed, 18 Dec 2024 10:53:42 +0000, > Shameer Kolothum wrote: > > > > Hi, > > > > v3 --> v4(Minor updates) > > https://lore.kernel.org/kvmarm/20241209115311.40496-1-shameerali.kolothum.thodi@huawei.com/ > > > > -Changed MIDR/REVIDR to 64 bits based on feedback from Connie > > and Marc(Patch #3). > > -Added R-by tags from Sebastian (Thanks!). > > Thanks again for putting this together. > > I think it would be really good to have a sample userspace > implementation of this extension so that we can play with it for real > before fully committing to it. > > I am also wondering is we should make it mandatory that a guest is > presented with an MIDR_EL1.Implementer value set to 0, which denotes > SW use, and would make it plain to the guest (and crucially, guest > userspace) that we are going to play tricks. > > Thoughts? I see no issues with giving userspace the option of doing this, but I'd rather not enforce this to use the PV interface. At least in a cloud setting it seems highly likely that you'd be running a mix of guests on the same VM definition, some aware of the PV interface and others not. If we use a software MIDR, all old VMs will lose errata mitigations and whatever else userspace might key off of MIDR. Userspace can make the call whether or not a VM can be migrated onto a different implementation based on whether or not the guest used the hypercall interface. And maybe just terminate the VM if it didn't. -- Thanks, Oliver