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Fri, 9 Apr 2021 14:56:29 +0000 Subject: Re: [PATCH v2] KVM: SVM: Make sure GHCB is mapped before updating To: Sean Christopherson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, Paolo Bonzini , Jim Mattson , Joerg Roedel , Vitaly Kuznetsov , Wanpeng Li , Borislav Petkov , Ingo Molnar , Thomas Gleixner , Brijesh Singh References: <1ed85188bee4a602ffad9632cdf5b5b5c0f40957.1617900892.git.thomas.lendacky@amd.com> <923548be-db20-7eea-33aa-571347a95526@amd.com> <3c28c9bf-d14e-3f9b-0973-ba4a438aaa33@amd.com> From: Tom Lendacky Message-ID: <87363a29-fa57-a2b2-4b42-6f2cd5e54dfd@amd.com> Date: Fri, 9 Apr 2021 09:56:27 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [67.79.209.213] X-ClientProxiedBy: SA0PR11CA0066.namprd11.prod.outlook.com (2603:10b6:806:d2::11) To DM5PR12MB1355.namprd12.prod.outlook.com (2603:10b6:3:6e::7) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from office-linux.texastahm.com (67.79.209.213) by SA0PR11CA0066.namprd11.prod.outlook.com (2603:10b6:806:d2::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4020.16 via Frontend Transport; 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Set SW_EXIT_INFO_2 to a >>>>>> * non-zero value. >>>>>> */ >>>>>> + if (WARN_ON_ONCE(!svm->ghcb)) >>>>> >>>>> Isn't this guest triggerable? I.e. send a SIPI without doing the reset hold? >>>>> If so, this should not WARN. >>>> >>>> Yes, it is a guest triggerable event. But a guest shouldn't be doing that, >>>> so I thought adding the WARN_ON_ONCE() just to detect it wasn't bad. >>>> Definitely wouldn't want a WARN_ON(). >>> >>> WARNs are intended only for host issues, e.g. a malicious guest shouldn't be >>> able to crash the host when running with panic_on_warn. >>> >> >> Ah, yeah, forgot about panic_on_warn. I can go back to the original patch >> or do a pr_warn_once(), any pref? > > No strong preference. If you think the print would be helpful for ongoing > development, then it's probably worth adding. For development, I'd want to see it all the time. But since it is guest triggerable, the _once() method is really needed in production. So in the latest version I just dropped the message/notification. Thanks, Tom >