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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 06856C43331 for ; Tue, 12 Nov 2019 05:38:47 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 877A821783 for ; Tue, 12 Nov 2019 05:38:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ozlabs.org header.i=@ozlabs.org header.b="hQVWmXDm" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 877A821783 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=ozlabs.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id E33856B0003; Tue, 12 Nov 2019 00:38:45 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id DE3FA6B0005; Tue, 12 Nov 2019 00:38:45 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CD4C46B0006; Tue, 12 Nov 2019 00:38:45 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0044.hostedemail.com [216.40.44.44]) by kanga.kvack.org (Postfix) with ESMTP id B7AA96B0003 for ; Tue, 12 Nov 2019 00:38:45 -0500 (EST) Received: from smtpin19.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id 7DF473499 for ; Tue, 12 Nov 2019 05:38:45 +0000 (UTC) X-FDA: 76146521010.19.hen75_121eefb0e3d3f X-HE-Tag: hen75_121eefb0e3d3f X-Filterd-Recvd-Size: 5374 Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) by imf46.hostedemail.com (Postfix) with ESMTP for ; Tue, 12 Nov 2019 05:38:44 +0000 (UTC) Received: by ozlabs.org (Postfix, from userid 1003) id 47BxPD2xJtz9sP3; Tue, 12 Nov 2019 16:38:40 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ozlabs.org; s=201707; t=1573537120; bh=SZoRRTRm9ztAOpkmJzAzQX6odqFqiF8GoxUebpLCgpc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hQVWmXDmoBI0+5xEt5CjywarL2yoySowzmAqTVwVg1xkSnDUgP/aU/UML3IcaW4O1 0JC0EzBb7RM+zH9EvbepmZRmTR/OJaFv7mn9NDOpFncCFKJha5Ur6FigHCBoIxbIt2 +l6CjnPsLU7W2Cmsgm5Ix3Hx20pHhHAMqRqxmBjU1TaxhW/UdZxiJuYSvRe1EZNNpa 51XwLhASGKTEueiKLuNJElxxNM5Ye28r+nyJCqBju1dcp3PUuYi4Ne4aIE5HKFJ9KR rH1nu1co4WZywoaXY/Rx+ww2ZHRGl8nCb0OIVp/AQYJMVKrExItkOArcA7oQS+heg4 wnpzJJGUtPlJg== Date: Tue, 12 Nov 2019 16:38:36 +1100 From: Paul Mackerras To: Ram Pai Cc: Bharata B Rao , linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org, linux-mm@kvack.org, paulus@au1.ibm.com, aneesh.kumar@linux.vnet.ibm.com, jglisse@redhat.com, cclaudio@linux.ibm.com, sukadev@linux.vnet.ibm.com, hch@lst.de, Sukadev Bhattiprolu , Ram Pai Subject: Re: [PATCH v10 7/8] KVM: PPC: Implement H_SVM_INIT_ABORT hcall Message-ID: <20191112053836.GB10885@oak.ozlabs.ibm.com> References: <20191104041800.24527-1-bharata@linux.ibm.com> <20191104041800.24527-8-bharata@linux.ibm.com> <20191111041924.GA4017@oak.ozlabs.ibm.com> <20191112010158.GB5159@oc0525413822.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191112010158.GB5159@oc0525413822.ibm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Nov 11, 2019 at 05:01:58PM -0800, Ram Pai wrote: > On Mon, Nov 11, 2019 at 03:19:24PM +1100, Paul Mackerras wrote: > > On Mon, Nov 04, 2019 at 09:47:59AM +0530, Bharata B Rao wrote: > > > From: Sukadev Bhattiprolu > > > > > > Implement the H_SVM_INIT_ABORT hcall which the Ultravisor can use to > > > abort an SVM after it has issued the H_SVM_INIT_START and before the > > > H_SVM_INIT_DONE hcalls. This hcall could be used when Ultravisor > > > encounters security violations or other errors when starting an SVM. > > > > > > Note that this hcall is different from UV_SVM_TERMINATE ucall which > > > is used by HV to terminate/cleanup an SVM. > > > > > > In case of H_SVM_INIT_ABORT, we should page-out all the pages back to > > > HV (i.e., we should not skip the page-out). Otherwise the VM's pages, > > > possibly including its text/data would be stuck in secure memory. > > > Since the SVM did not go secure, its MSR_S bit will be clear and the > > > VM wont be able to access its pages even to do a clean exit. > > > > It seems fragile to me to have one more transfer back into the > > ultravisor after this call. Why does the UV need to do this call and > > then get control back again one more time? > > Why can't the UV defer > > doing this call until it can do it without expecting to see a return > > from the hcall? > > Sure. But, what if the hypervisor calls back into the UV through a > ucall, asking for some page to be paged-out? If the ultravisor has > cleaned up the state associated with the SVM, it wont be able to service > that request. > > H_SVM_INIT_ABORT is invoked to tell the hypervisor that the > secure-state-transition for the VM cannot be continued any further. > Hypervisor can than choose to do whatever with that information. It can > cleanup its state, and/or make ucalls to get some information from the > ultravisor. It can also choose not to return control back to the ultravisor. > > > > And if it does need to see a return from the hcall, > > what would happen if a malicious hypervisor doesn't do the return? > > That is fine. At most it will be a denail-of-service attack. > > RP > > > > > Paul. > > > > > > If the ultravisor cleans up the SVM's state on its side and then informs > the Hypervisor to abort the SVM, the hypervisor will not be able to > cleanly terminate the VM. Because to terminate the SVM, the hypervisor > still needs the services of the Ultravisor. For example: to get the > pages back into the hypervisor if needed. Another example is, the > hypervisor can call UV_SVM_TERMINATE. Regardless of which ucall > gets called, the ultravisor has to hold on to enough state of the > SVM to service that request. OK, that's a good reason. That should be explained in the commit message. > The current design assumes that the hypervisor explicitly informs the > ultravisor, that it is done with the SVM, through the UV_SVM_TERMINATE > ucall. Till that point the Ultravisor must to be ready to service any > ucalls made by the hypervisor on the SVM's behalf. I see that UV_SVM_TERMINATE is done when the VM is being destroyed (at which point kvm->arch.secure_guest doesn't matter any more), and in kvmhv_svm_off(), where kvm->arch.secure_guest gets cleared explicitly. Hence I don't see any need for clearing it in the assembly code on the next secure guest entry. I think the change to book3s_hv_rmhandlers.S can just be dropped. Paul.