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b=DOfvnLOdMThku2eCqcKDEmLLhXA4+6z/J36rP6a2BcxftAsej0LJ7sId5j+kFXAOKJzCYvzNfxTw5rIh7l6QbSa4NNRvgmpOS5R3uCCHJfoVnWbX0GK6gFUSExKvZCdRb2ZH/kOD0Uljsq6DEbGW+zNvTLmItaDbT2o26y5OxAQ= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from BL3PR12MB9049.namprd12.prod.outlook.com (2603:10b6:208:3b8::21) by CH3PR12MB9194.namprd12.prod.outlook.com (2603:10b6:610:19f::7) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.7918.27; Wed, 4 Sep 2024 19:44:37 +0000 Received: from BL3PR12MB9049.namprd12.prod.outlook.com ([fe80::c170:6906:9ef3:ecef]) by BL3PR12MB9049.namprd12.prod.outlook.com ([fe80::c170:6906:9ef3:ecef%7]) with mapi id 15.20.7918.024; Wed, 4 Sep 2024 19:44:37 +0000 Message-ID: <89cef849-4309-478c-8250-3e668943fa15@amd.com> Date: Wed, 4 Sep 2024 14:44:33 -0500 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] x86/sev: Fix host kdump support for SNP Content-Language: en-US From: "Kalra, Ashish" To: Sean Christopherson Cc: pbonzini@redhat.com, dave.hansen@linux.intel.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, peterz@infradead.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, thomas.lendacky@amd.com, michael.roth@amd.com, kexec@lists.infradead.org, linux-coco@lists.linux.dev References: <20240903191033.28365-1-Ashish.Kalra@amd.com> In-Reply-To: Content-Type: text/plain; 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>>> sev->snp_context = NULL; >>> >>> + if (snp_asid_to_gctx_pages_map) >>> + snp_asid_to_gctx_pages_map[sev_get_asid(kvm)] = NULL; >>> + >>> return 0; >>> } >>> >>> +static void __snp_decommission_all(void) >>> +{ >>> + struct sev_data_snp_addr data = {}; >>> + int ret, asid; >>> + >>> + if (!snp_asid_to_gctx_pages_map) >>> + return; >>> + >>> + for (asid = 1; asid < min_sev_asid; asid++) { >>> + if (snp_asid_to_gctx_pages_map[asid]) { >>> + data.address = __sme_pa(snp_asid_to_gctx_pages_map[asid]); >> NULL pointer deref if this races with snp_decommission_context() from task >> context. Actually looking at this again, this is why we really need all CPUs synchronizing in NMI context before one CPU in NMI context takes control and issues SNP_DECOMMISSION on all SNP VMs. If there are sev_vm_destroy() -> snp_decommision_context() executing,  when they start handling NMI they would have either already issued SNP_DECOMMISSION for this VM and/or reclaimed the SNP guest context page (transitioned to FW state after SNP_DECOMMISSION). In both cases when we issue SNP_DECOMMISSION here in __snp_decommission_all(), the command will fail with INVALID_GUEST/INVALID_ADDRESS error, so we can simply ignore this error and assume that the VM has already been decommissioned and continue with decommissioning the other VMs. I actually tested some of these scenarios and they work as above. >>> + ret = sev_do_cmd(SEV_CMD_SNP_DECOMMISSION, &data, NULL); >>> + if (!ret) { >> And what happens if SEV_CMD_SNP_DECOMMISSION fails? As mentioned above, we can ignore the failure here as the VM may have already been decommissioned. In the case where SNP_DECOMMISSION fails without the VM being already decommissioned, crashkernel boot will fail. Thanks, Ashish