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Received-SPF: Pass (protection.outlook.com: domain of amd.com designates 165.204.84.17 as permitted sender) receiver=protection.outlook.com; client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by SJ1PEPF000023CB.mail.protection.outlook.com (10.167.244.5) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.7897.11 via Frontend Transport; Tue, 20 Aug 2024 15:26:53 +0000 Received: from [10.236.30.70] (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Tue, 20 Aug 2024 10:26:52 -0500 Message-ID: Date: Tue, 20 Aug 2024 10:26:51 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] KVM: SEV: Configure "ALLOWED_SEV_FEATURES" VMCB Field To: Sean Christopherson CC: , , , Tom Lendacky , Michael Roth , Ashish Kalra , Nikunj A Dadhania , Borislav Petkov , Dave Hansen , Paolo Bonzini , Ingo Molnar , "H. Peter Anvin" , Thomas Gleixner , "Kishon Vijay Abraham I" References: <20240802015732.3192877-1-kim.phillips@amd.com> <20240802015732.3192877-3-kim.phillips@amd.com> <7208a5ac-282c-4ff5-9df2-87af6bcbcc8a@amd.com> Content-Language: en-US From: Kim Phillips Autocrypt: addr=kim.phillips@amd.com; keydata= xsBNBFh3uA4BCACmMh2JZ9f6vavU7XWTg45pl64x61cugDKZ34jiRLohU280rECk+kyXrKGB GdtV5+8tZWhMCyn151/C/OEYIi3CP5DY6wyrjbFkhI8ohqR4VqyC9gWAqD25coTQpOHyt7pd 8EvSBDAuL031gqw5w6JNeqEbMplZeToy5Rgdr1i35MZOzyIaO01H+F2/sOL7qk6pY21y5Flj ojjFT/uWg7eodnOu/BJ1Uem6FaO6ovYSAMOaCs/GpguznsS76ORsH6Jnyp6+e3KlZe/F2M7H 5HWCVsS5np2rf1luDsfHKV7HCd2+4iFRhxjbbulSBRMn7zx16PEGh8ccNwJm9/nwof6jABEB AAHNI0tpbSBQaGlsbGlwcyA8a2ltLnBoaWxsaXBzQGFtZC5jb20+wsCOBBMBCgA4FiEEaBZs 4ROWXWKVJWj8Z9viHdU8iO8FAmHm/zMCGwMFCwkIBwIGFQoJCAsCBBYCAwECHgECF4AACgkQ Z9viHdU8iO8aXQgAnByD4TUD+xGXXDAkIopwqip2Vfy3qzNhmfzdvLxKxsb6I6Tf1l2pMPGP EHxDPfuQhheyh+iRWrba6flwBGaNriJTFuVpQUGoRcjV11F2cpEbToqv2LGPaXIpc7IxEoRt lg9VKr70XcRePKq4iH5e7wrmzACP9UlvaKlRJl97FTckZIguQQMZe9kqLga1yRDqcQVN5Kj6 IP6V8WzRz0qGpVE1GE/vjYH13o2qHrvp9d/zlPBTZFwhNpLBn4JHohyxQ63t7eZ1L4U66Caq jZ0lhdN/psHJWab0SeIIRAG5+WLMcRbx3+LPjzIyrXJSonsm4t5lU3RmGmWwJSunxGDu1s7A TQRYd7gOAQgAp2VJv7J5eaWVdHvazWijdobOXSa13GnV8DXENQLQSSQlxGkLkYa3nDHr6Xjk z2NPFn4cf8GgMd7Bd4p3MR6DbwA4qKE+8ZW2x4XdH///HGDDEI69sDZEzLPXgl/9dv49dxym Q/nuco2KtF4xaMS/mjRsv7Eu5oGH+2+vPKe7L8ykXUh7SJmr0tI2/y9A6MVOPckdenywmKQ+ 6R0gw6aL2OeUyWZLS/e/3+0zFmQxeTyHpoJb8cNk/XqUGsBXsTO6y+7fdykpXNCfeJL/bSGE SXgwRROHCnQeKwVbbvEU/e5GZlNnKXoD7u2jyJxt4NTG2c0Jze+W3MPwh1wxzNg6BQARAQAB wsBfBBgBCAAJBQJYd7gOAhsMAAoJEGfb4h3VPIjv33EIAIRVHWqFbAYPZZtYKdwugwzL0FKa X0VbkUvKNG8SQAcdvkKmnSITWrIbecHPQaSqrtl/W8qKD6YFNOC9JNCHEfyLPTxo33WonQpo utm5nbRS1p45Mk65Uu76qhuHMjPnOgbMqmRHgWjIRiNfKm1QD5/3bml08HnJ1PuucuxI4HkK SWR00RE4Jyhxi1ISB3UEQ98iZtobAkTYa3aZ6xCZzd+v+o4CkLDKtS8vrBXpppi/HAeRlL7m waGKsjcegLX8cEHSblIct+9KKjUrE8uZyokt67sTYDlPapVCkhTtKn5O88jXkqA2PgAU6XqP KeUe7zYeAD22yc9K+Ovi7bZ9I5o= In-Reply-To: Content-Type: text/plain; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Aug 2024 15:26:53.3937 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: fc744972-01a8-4392-0838-08dcc12c8519 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SJ1PEPF000023CB.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ2PR12MB8942 On 8/19/24 5:23 PM, Sean Christopherson wrote: > On Mon, Aug 19, 2024, Kim Phillips wrote: >> On 8/16/24 5:59 PM, Sean Christopherson wrote: >>> On Thu, Aug 01, 2024, Kim Phillips wrote: >>>> From: Kishon Vijay Abraham I >>>> >>>> AMD EPYC 5th generation processors have introduced a feature that allows >>>> the hypervisor to control the SEV_FEATURES that are set for or by a >>>> guest [1]. The ALLOWED_SEV_FEATURES feature can be used by the hypervisor >>>> to enforce that SEV-ES and SEV-SNP guests cannot enable features that the >>>> hypervisor does not want to be enabled. >>> >>> How does the host communicate to the guest which features are allowed? >> >> I'm not familiar with any future plans to negotiate with the guest directly, > > I feel like I'm missing something. What happens if the guest wants to enable > PmcVirtualization and it's unexpectedly disallowed? Does the guest simply panic? In SNP, VMRUN will return with an exit code of VMEXIT_INVALID (0xffffffff) if the guest tries to set it. In SEV-ES, the hypervisor can set it, and the same thing will happen to VMRUN. In both cases, SEV_FEATURES is saved to VMCB field GUEST_SEV_FEATURES at offset 140h on the VMEXIT, indicating to the host which feature was attempted but caught as not allowed. >> but since commit ac5c48027bac ("KVM: SEV: publish supported VMSA features"), >> userspace can retrieve sev_supported_vmsa_features via an ioctl. >> >>> And based on this blurb: >>> >>> Some SEV features can only be used if the Allowed SEV Features Mask is enabled, >>> and the mask is configured to permit the corresponding feature. If the Allowed >>> SEV Features Mask is not enabled, these features are not available (see SEV_FEATURES >>> in Appendix B, Table B-4). >>> >>> and the appendix, this only applies to PmcVirtualization and SecureAvic. Adding >>> that info in the changelog would be *very* helpful. >> >> Ok, how about adding: >> >> "The PmcVirtualization and SecureAvic features explicitly require >> ALLOWED_SEV_FEATURES to enable them before they can be used." >> >>> And I see that SVM_SEV_FEAT_DEBUG_SWAP, a.k.a. DebugVirtualization, is a guest >>> controlled feature and doesn't honor ALLOWED_SEV_FEATURES. Doesn't that mean >>> sev_vcpu_has_debug_swap() is broken, i.e. that KVM must assume the guest can >>> DebugVirtualization on and off at will? Or am I missing something? >> >> My understanding is that users control KVM's DEBUG_SWAP setting >> with a module parameter since commit 4dd5ecacb9a4 ("KVM: SEV: allow >> SEV-ES DebugSwap again"). If the module parameter is not set, with >> this patch, VMRUN will fail since the host doesn't allow DEBUG_SWAP. > > But that's just KVM's view of vmsa_features. With SNP's wonderful > SVM_VMGEXIT_AP_CREATE, can't the guest create a VMSA with whatever sev_features > it wants, so long as they aren't host-controllable, i.e. aren't PmcVirtualization > or SecureAvic? No, as above, if the guest tries any silly business the host will get a VMEXIT_INVALID, no matter if using the feature *requires* ALLOWED_SEV_FEATURES to be enabled and explicitly allow it (currently PmcVirtualization or SecureAvic). Kim