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Thu, 4 Jul 2024 08:10:38 +0000 Date: Thu, 4 Jul 2024 16:09:19 +0800 From: Yan Zhao To: "Edgecombe, Rick P" CC: "linux-kernel@vger.kernel.org" , "seanjc@google.com" , "Huang, Kai" , "sagis@google.com" , "isaku.yamahata@gmail.com" , "Aktas, Erdem" , "dmatlack@google.com" , "kvm@vger.kernel.org" , "Yamahata, Isaku" , "pbonzini@redhat.com" Subject: Re: [PATCH v3 13/17] KVM: x86/tdp_mmu: Support mirror root for TDP MMU Message-ID: Reply-To: Yan Zhao References: <20240619223614.290657-1-rick.p.edgecombe@intel.com> <20240619223614.290657-14-rick.p.edgecombe@intel.com> <70dab5f4fb69c072493efe4b3198305ae262b545.camel@intel.com> <7268ff80d3825fa6d7a50101358b47d5fbe86d5c.camel@intel.com> Content-Type: text/plain; charset="iso-8859-1" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <7268ff80d3825fa6d7a50101358b47d5fbe86d5c.camel@intel.com> X-ClientProxiedBy: SI2PR02CA0037.apcprd02.prod.outlook.com (2603:1096:4:196::8) To DS7PR11MB5966.namprd11.prod.outlook.com (2603:10b6:8:71::6) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MN0PR11MB5964:EE_|PH7PR11MB6748:EE_ X-MS-Office365-Filtering-Correlation-Id: f0b3695c-acb6-4c78-b3ae-08dc9c00c97e X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|1800799024; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?iso-8859-1?Q?wby8nipfq8VHJbpZvWozKufG9jPc2e6f72Ieeyt6y1JfUx+0TmK/688NFM?= =?iso-8859-1?Q?OxowKkFgTW5YGvKcgl9bdon6jPNe7H5W8yj854i34i1BtI+vMqA8++wc8F?= =?iso-8859-1?Q?gBx67ojQaNPRFHFxe8+OpC5ZWNVZlLzcVPRpzgxhbqczFzj/qboPUEDx2N?= =?iso-8859-1?Q?uoMoYtpdLTYNvNudO7urRWb8/NxsfM/Gyn6MFOaKsbT4qTL6OZqZlJubQf?= =?iso-8859-1?Q?VGXTOIiDH+eOGi8Y7CrqzPVdwF8TAV4FnkX+U0kg2Nf+6vWmPI+8PNksne?= =?iso-8859-1?Q?w7H8H0w6fPAQfdzGhBdN7xQgB0gy0aF3itsWxaPr7TMlS5Xc7t0EpNBV1F?= =?iso-8859-1?Q?D4M1dDv1vnUJv//RHhPD0VvyBvbm5X3GmPotSpoZfE3ptpz1bvKq/WSejL?= =?iso-8859-1?Q?WqqgimDA316JqUXiRsUgjTwgZ+371u6hyUxl0hv2+ivu/d+YefxAvGJ2Lq?= =?iso-8859-1?Q?X6woZwU4blwq5G0pLZNjP37FTihu0V2fcH+cTiFEY9hHUoyh7C4k8IsVrB?= =?iso-8859-1?Q?OABzJs48oiIDdDmejxWBmr0ckeiR0BX/CGJ9+oIv3RfZV4vg9PeWXiPTe4?= =?iso-8859-1?Q?4h/3OHEa7S2q/vRJXuBUObFCfvTH7049oufxgl+SZNlABGCbVwNcpzY/AM?= =?iso-8859-1?Q?PcVxC3lCOPSJrcIa4jCEC32lyTh62gfYj9pVmK8KTpPqR9nAw33C5IxrNf?= =?iso-8859-1?Q?jDdCPv1IqiyQ6CXntN/yv2JrQm3Cznij9m9ZekGMfjoQEdnsrmzfyAWGHv?= =?iso-8859-1?Q?L4Whp4JtfB3ikwi8K9B4iVYAVuDmFl1egO2uk1m9M/75vACruzZRwW83BR?= =?iso-8859-1?Q?pzefy+7w6dcsvICyQC2Gn/SKjVv+n7ZBk7jTl0ynr2CoHeJhcKKTIWJbiI?= =?iso-8859-1?Q?EcXxCl5D9DYN7PalR/L9exz+AL+bNB73stJQxF4bMFDuHjWBQHDFPra4PV?= =?iso-8859-1?Q?oQvua42nn/lKqgomCBbGSA+vZmC0Vg19mK02+xa6sEVcbNEFieiAO4hY3O?= =?iso-8859-1?Q?rjCjWgp63aO1tXyAENl+c3quZ4FbmG90XY/7HwcuouqCWjjbaQTu9O5xPY?= =?iso-8859-1?Q?OHhNnDYa7jTrCIgxuxXfhbaYHrYzBeXTzDeLFHPE3Wghp2jsQNUbBZIR//?= =?iso-8859-1?Q?10KFLe47T+R2FuktKLthXvdqb5VkqJTVdkagwwP0rjFuGC/jAsbBHxmGHC?= =?iso-8859-1?Q?4KbIEOPLtYRqHiDpehxV+wODiIH7K2oDc1+CZaNlACeILHhcadDmUR5hw/?= =?iso-8859-1?Q?pbGwrKiwsspVjNU5C6xbNwwtErqdRNGGbCGuUDZycsXKQ/tJ2zyTLXkkBP?= =?iso-8859-1?Q?OXOmavmWeoUqSdBWwiykQ8dT9csW3Hn8VYY02kGGPc257/tLZ+QfaLV4Xs?= =?iso-8859-1?Q?Q5T9QqKrtbD0DyGuFx4atgLuG/nR0TxD3JQmJMaehsyG54UcKk4OFSyI6V?= =?iso-8859-1?Q?VO+ayjRPDcjHRypxFATeCRComohZkLO13VMMu76+5dfIQgTRLq8xmfUwcT?= =?iso-8859-1?Q?opoegisXHEy41VwTf0jTV0iJ5pwhVTwtaBXy0Zmq+DnsOkyL9Hagq0xL9R?= =?iso-8859-1?Q?H0Va0aMh4/d4TfL36XtSx2AhR1wC5iN+vEK09FtK4NuAIApAdyO7EdIU5u?= =?iso-8859-1?Q?Ha2xWAK6AgXDGX72jnkJuG+QQJVQMkMCFo?= X-MS-Exchange-CrossTenant-Network-Message-Id: f0b3695c-acb6-4c78-b3ae-08dc9c00c97e X-MS-Exchange-CrossTenant-AuthSource: DS7PR11MB5966.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 Jul 2024 08:10:38.1702 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: d/NAsIPBO8BTcaJdJtdQGTIs5Z3gnQBSAM5aHnN0+PD4HfUeyDqmDTjMpQJtePZfW/mbeDrWXqwNL+dnH/DXJg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR11MB6748 X-OriginatorOrg: intel.com On Thu, Jul 04, 2024 at 03:40:35AM +0800, Edgecombe, Rick P wrote: > On Wed, 2024-06-26 at 13:05 +0800, Yan Zhao wrote: > > But we still need the reload path to have each vcpu to hold a ref count of the > > mirror root. > > What about below fix? > > > > diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h > > index 026e8edfb0bd..4decd13457ec 100644 > > --- a/arch/x86/kvm/mmu.h > > +++ b/arch/x86/kvm/mmu.h > > @@ -127,9 +127,28 @@ void kvm_mmu_sync_prev_roots(struct kvm_vcpu *vcpu); > >  void kvm_mmu_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new, > >                          int bytes); > > > > +static inline bool kvm_has_mirrored_tdp(const struct kvm *kvm) > > +{ > > +       return kvm->arch.vm_type == KVM_X86_TDX_VM; > > +} > > + > > +static inline bool kvm_mmu_root_hpa_is_invalid(struct kvm_vcpu *vcpu) > > +{ > > +       return vcpu->arch.mmu->root.hpa == INVALID_PAGE; > > +} > > + > > +static inline bool kvm_mmu_mirror_root_hpa_is_invalid(struct kvm_vcpu *vcpu) > > +{ > > +       if (!kvm_has_mirrored_tdp(vcpu->kvm)) > > +               return false; > > + > > +       return vcpu->arch.mmu->mirror_root_hpa == INVALID_PAGE; > > +} > > + > >  static inline int kvm_mmu_reload(struct kvm_vcpu *vcpu) > >  { > > -       if (likely(vcpu->arch.mmu->root.hpa != INVALID_PAGE)) > > +       if (!kvm_mmu_root_hpa_is_invalid(vcpu) && > > +           !kvm_mmu_mirror_root_hpa_is_invalid(vcpu)) > > If we go this way, we should keep the likely. But, I'm not convinced. > > >                 return 0; > > > >         return kvm_mmu_load(vcpu); > > @@ -322,11 +341,6 @@ static inline gpa_t kvm_translate_gpa(struct kvm_vcpu > > *vcpu, > >         return translate_nested_gpa(vcpu, gpa, access, exception); > >  } > > > > -static inline bool kvm_has_mirrored_tdp(const struct kvm *kvm) > > -{ > > -       return kvm->arch.vm_type == KVM_X86_TDX_VM; > > -} > > - > >  static inline gfn_t kvm_gfn_direct_bits(const struct kvm *kvm) > >  { > >         return kvm->arch.gfn_direct_bits; > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > > index e1299eb03e63..5e7d92074f70 100644 > > --- a/arch/x86/kvm/mmu/mmu.c > > +++ b/arch/x86/kvm/mmu/mmu.c > > @@ -3702,9 +3702,11 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu > > *vcpu) > >         int r; > > > >         if (tdp_mmu_enabled) { > > -               if (kvm_has_mirrored_tdp(vcpu->kvm)) > > +               if (kvm_mmu_mirror_root_hpa_is_invalid(vcpu)) > >                         kvm_tdp_mmu_alloc_root(vcpu, true); > > -               kvm_tdp_mmu_alloc_root(vcpu, false); > > + > > +               if (kvm_mmu_root_hpa_is_invalid(vcpu)) > > +                       kvm_tdp_mmu_alloc_root(vcpu, false); > > So we can have either: > mirror_root_hpa = INVALID_PAGE > root.hpa = INVALID_PAGE > > or: > mirror_root_hpa = root > root.hpa = INVALID_PAGE > > We don't ever have: > mirror_root_hpa = INVALID_PAGE > root.hpa = root > > Because mirror_root_hpa is special. > Good point. > >                 return 0; > >         } > > > > Having the check in kvm_mmu_reload() and here both is really ugly.  Right now we > have kvm_mmu_reload() which only allocates new roots if needed, then > kvm_mmu_load() goes and allocates/references them. Now mmu_alloc_direct_roots() > has the same logic to only reload as needed. > > So could we just leave the kvm_mmu_reload() logic as is, and just have special > logic in mmu_alloc_direct_roots() to not avoid re-allocating mirror roots? This > is actually what v19 had, but it was thought to be a historical relic: > "Historically we needed it. We don't need it now. We can drop it." > https://lore.kernel.org/kvm/20240325200122.GH2357401@ls.amr.corp.intel.com/ > > So just have this small fixup instead? Yes. > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index ae5d5dee86af..2e062178222e 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -3705,7 +3705,8 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu) > int r; > > if (tdp_mmu_enabled) { > - if (kvm_has_mirrored_tdp(vcpu->kvm)) > + if (kvm_has_mirrored_tdp(vcpu->kvm) && > + !VALID_PAGE(mmu->mirror_root_hpa)) > kvm_tdp_mmu_alloc_root(vcpu, true); > kvm_tdp_mmu_alloc_root(vcpu, false); > return 0; > Perhaps also a comment in kvm_mmu_reload() to address concerns like why checking only root.hpa in kvm_mmu_reload() is enough. diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h index 03737f3aaeeb..aba98c8cc67d 100644 --- a/arch/x86/kvm/mmu.h +++ b/arch/x86/kvm/mmu.h @@ -129,6 +129,15 @@ void kvm_mmu_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new, static inline int kvm_mmu_reload(struct kvm_vcpu *vcpu) { + /* + * Checking root.hpa is sufficient even when KVM has mirror root. + * We can have either: + * (1) mirror_root_hpa = INVALID_PAGE, root.hpa = INVALID_PAGE + * (2) mirror_root_hpa = root , root.hpa = INVALID_PAGE + * (3) mirror_root_hpa = root1, root.hpa = root2 + * We don't ever have: + * mirror_root_hpa = INVALID_PAGE, root.hpa = root + */ if (likely(vcpu->arch.mmu->root.hpa != INVALID_PAGE)) return 0; diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index a5f803f1d17e..eee35e958971 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -3705,7 +3705,8 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu) int r; if (tdp_mmu_enabled) { - if (kvm_has_mirrored_tdp(vcpu->kvm)) + if (kvm_has_mirrored_tdp(vcpu->kvm) && + !VALID_PAGE(mmu->mirror_root_hpa)) kvm_tdp_mmu_alloc_root(vcpu, true); kvm_tdp_mmu_alloc_root(vcpu, false); return 0;