From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3A0BCC4361B for ; Wed, 9 Dec 2020 04:17:37 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 30AFA23770 for ; Wed, 9 Dec 2020 04:17:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 30AFA23770 Authentication-Results: mail.kernel.org; dmarc=pass (p=none dis=none) header.from=ozlabs.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4CrP0F530pzDqnR for ; Wed, 9 Dec 2020 15:17:33 +1100 (AEDT) Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (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 lists.ozlabs.org (Postfix) with ESMTPS id 4CrNyW1BY4zDqYM for ; Wed, 9 Dec 2020 15:16:03 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=ozlabs.org Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; secure) header.d=ozlabs.org header.i=@ozlabs.org header.a=rsa-sha256 header.s=201707 header.b=Gz4ZDncc; dkim-atps=neutral Received: by ozlabs.org (Postfix, from userid 1003) id 4CrNyV6X4sz9sWC; Wed, 9 Dec 2020 15:16:02 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ozlabs.org; s=201707; t=1607487362; bh=jqtZFI7KL7v46Pp3s+SsaUNEfvanCrhY8vPaiiWNGA8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Gz4ZDnccQU+sPGtfKTwUSUDh7N8XvvpczzIgXv7JISlKiCzQVqCAsPdlSuW+A7Gfq z3R4wyUqc6eGJLQBgNIDCiX2+BI9szVsYjR6Os8lqeX9UJKJznIYJWYBf0JPIZnJLC KssI9r/eaho7i1UpIa7ghOfnnVWGZyfNgPvwuJXjkKIpM7LFDKwGQMFtcuRD68a/rJ Xce8SAKlRLtnF1dthsJO5EC29H3Y95tsH9VFY1OE7fCMLRyJenZI3K7KVUMwQS4FBI GG3HUXbionHOVT/NF7hwYoVg8bafbns0Ie8Wmbd+1GYDQx968Qysh4+liKDdnguWJd GKRGvDE+l9Yww== Date: Wed, 9 Dec 2020 15:15:42 +1100 From: Paul Mackerras To: Bharata B Rao Subject: Re: [PATCH v1 1/2] KVM: PPC: Book3S HV: Add support for H_RPT_INVALIDATE (nested case only) Message-ID: <20201209041542.GA29825@thinks.paulus.ozlabs.org> References: <20201019112642.53016-1-bharata@linux.ibm.com> <20201019112642.53016-2-bharata@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201019112642.53016-2-bharata@linux.ibm.com> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: aneesh.kumar@linux.ibm.com, npiggin@gmail.com, kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, David Gibson Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Mon, Oct 19, 2020 at 04:56:41PM +0530, Bharata B Rao wrote: > Implements H_RPT_INVALIDATE hcall and supports only nested case > currently. > > A KVM capability KVM_CAP_RPT_INVALIDATE is added to indicate the > support for this hcall. I have a couple of questions about this patch: 1. Is this something that is useful today, or is it something that may become useful in the future depending on future product plans? In other words, what advantage is there to forcing L2 guests to use this hcall instead of doing tlbie themselves? 2. Why does it need to be added to the default-enabled hcall list? There is a concern that if this is enabled by default we could get the situation where a guest using it gets migrated to a host that doesn't support it, which would be bad. That is the reason that all new things like this are disabled by default and only enabled by userspace (i.e. QEMU) in situations where we can enforce that it is available on all hosts to which the VM might be migrated. Thanks, Paul.