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Mon, 21 Jul 2025 09:45:31 -0700 (PDT) Date: Mon, 21 Jul 2025 09:45:29 -0700 In-Reply-To: <20250717162731.446579-5-tabba@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250717162731.446579-1-tabba@google.com> <20250717162731.446579-5-tabba@google.com> Message-ID: Subject: Re: [PATCH v15 04/21] KVM: x86: Introduce kvm->arch.supports_gmem From: Sean Christopherson To: Fuad Tabba Cc: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, kvmarm@lists.linux.dev, pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, viro@zeniv.linux.org.uk, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, xiaoyao.li@intel.com, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@google.com, ackerleytng@google.com, mail@maciej.szmigiero.name, david@redhat.com, michael.roth@amd.com, wei.w.wang@intel.com, liam.merwick@oracle.com, isaku.yamahata@gmail.com, kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com, steven.price@arm.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com, quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, catalin.marinas@arm.com, james.morse@arm.com, yuzenghui@huawei.com, oliver.upton@linux.dev, maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com, roypat@amazon.co.uk, shuah@kernel.org, hch@infradead.org, jgg@nvidia.com, rientjes@google.com, jhubbard@nvidia.com, fvdl@google.com, hughd@google.com, jthoughton@google.com, peterx@redhat.com, pankaj.gupta@amd.com, ira.weiny@intel.com Content-Type: text/plain; charset="us-ascii" On Thu, Jul 17, 2025, Fuad Tabba wrote: > Introduce a new boolean member, supports_gmem, to kvm->arch. > > Previously, the has_private_mem boolean within kvm->arch was implicitly > used to indicate whether guest_memfd was supported for a KVM instance. > However, with the broader support for guest_memfd, it's not exclusively > for private or confidential memory. Therefore, it's necessary to > distinguish between a VM's general guest_memfd capabilities and its > support for private memory. > > This new supports_gmem member will now explicitly indicate guest_memfd > support for a given VM, allowing has_private_mem to represent only > support for private memory. > > Reviewed-by: Ira Weiny > Reviewed-by: Gavin Shan > Reviewed-by: Shivank Garg > Reviewed-by: Vlastimil Babka > Reviewed-by: Xiaoyao Li > Co-developed-by: David Hildenbrand > Signed-off-by: David Hildenbrand > Signed-off-by: Fuad Tabba NAK, this introduces unnecessary potential for bugs, e.g. KVM will get a false negative if kvm_arch_supports_gmem() is invoked before kvm_x86_ops.vm_init(). Patch 2 makes this a moot point because kvm_arch_supports_gmem() can simply go away. > --- > arch/x86/include/asm/kvm_host.h | 3 ++- > arch/x86/kvm/svm/svm.c | 1 + > arch/x86/kvm/vmx/tdx.c | 1 + > arch/x86/kvm/x86.c | 4 ++-- > 4 files changed, 6 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index bde811b2d303..938b5be03d33 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -1348,6 +1348,7 @@ struct kvm_arch { > u8 mmu_valid_gen; > u8 vm_type; > bool has_private_mem; > + bool supports_gmem; > bool has_protected_state; > bool pre_fault_allowed; > struct hlist_head mmu_page_hash[KVM_NUM_MMU_PAGES]; > @@ -2277,7 +2278,7 @@ void kvm_configure_mmu(bool enable_tdp, int tdp_forced_root_level, > > #ifdef CONFIG_KVM_GMEM > #define kvm_arch_has_private_mem(kvm) ((kvm)->arch.has_private_mem) > -#define kvm_arch_supports_gmem(kvm) kvm_arch_has_private_mem(kvm) > +#define kvm_arch_supports_gmem(kvm) ((kvm)->arch.supports_gmem) > #else > #define kvm_arch_has_private_mem(kvm) false > #define kvm_arch_supports_gmem(kvm) false > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index ab9b947dbf4f..d1c484eaa8ad 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -5181,6 +5181,7 @@ static int svm_vm_init(struct kvm *kvm) > to_kvm_sev_info(kvm)->need_init = true; > > kvm->arch.has_private_mem = (type == KVM_X86_SNP_VM); > + kvm->arch.supports_gmem = (type == KVM_X86_SNP_VM); > kvm->arch.pre_fault_allowed = !kvm->arch.has_private_mem; > } > > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c > index f31ccdeb905b..a3db6df245ee 100644 > --- a/arch/x86/kvm/vmx/tdx.c > +++ b/arch/x86/kvm/vmx/tdx.c > @@ -632,6 +632,7 @@ int tdx_vm_init(struct kvm *kvm) > > kvm->arch.has_protected_state = true; > kvm->arch.has_private_mem = true; > + kvm->arch.supports_gmem = true; > kvm->arch.disabled_quirks |= KVM_X86_QUIRK_IGNORE_GUEST_PAT; > > /* > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 357b9e3a6cef..adbdc2cc97d4 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -12780,8 +12780,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) > return -EINVAL; > > kvm->arch.vm_type = type; > - kvm->arch.has_private_mem = > - (type == KVM_X86_SW_PROTECTED_VM); > + kvm->arch.has_private_mem = (type == KVM_X86_SW_PROTECTED_VM); > + kvm->arch.supports_gmem = (type == KVM_X86_SW_PROTECTED_VM); > /* Decided by the vendor code for other VM types. */ > kvm->arch.pre_fault_allowed = > type == KVM_X86_DEFAULT_VM || type == KVM_X86_SW_PROTECTED_VM; > -- > 2.50.0.727.gbf7dc18ff4-goog >