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AJvYcCXUuX8wQ3SXY399VMWq/rje3YQduePMoXlDJHOLobgUGvDjKijJVEEvxfEzkHshrqNEfs77eR66608=@vger.kernel.org X-Gm-Message-State: AOJu0Yy5bkl7FVkWBt/QoFPTDiH/PJxUAh/JzFFDm5dq2hAW2VjgSa3t d2KTumcgnZE1LCcG4lWgSC+vD9u6P2coo8jx4SJyIn3T7hxY7AUgCDABVoKbfh8olpEeIwh6XFA 5IAnNLErrppEQstB9E5g0SFFaSQ== X-Google-Smtp-Source: AGHT+IHD5TZ3PlH4BoXojkeR7Hq6pa25rPFAC44tSG4hp0SVSWugJiynOfGyj0/LVdH6RcIi4tLRlKxt4/SfCTBJBg== X-Received: from pjbfv10.prod.google.com ([2002:a17:90b:e8a:b0:33b:ab61:4f71]) (user=ackerleytng job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:f70b:b0:283:c950:a76f with SMTP id d9443c01a7336-290cc2f91d2mr289431935ad.43.1761173129640; Wed, 22 Oct 2025 15:45:29 -0700 (PDT) Date: Wed, 22 Oct 2025 15:45:28 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <8ee16fbf254115b0fd72cc2b5c06d2ccef66eca9.1760731772.git.ackerleytng@google.com> <2457cb3b-5dde-4ca1-b75d-174b5daee28a@arm.com> Message-ID: Subject: Re: [RFC PATCH v1 07/37] KVM: Introduce KVM_SET_MEMORY_ATTRIBUTES2 From: Ackerley Tng To: Steven Price , cgroups@vger.kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, x86@kernel.org Cc: akpm@linux-foundation.org, binbin.wu@linux.intel.com, bp@alien8.de, brauner@kernel.org, chao.p.peng@intel.com, chenhuacai@kernel.org, corbet@lwn.net, dave.hansen@intel.com, dave.hansen@linux.intel.com, david@redhat.com, dmatlack@google.com, erdemaktas@google.com, fan.du@intel.com, fvdl@google.com, haibo1.xu@intel.com, hannes@cmpxchg.org, hch@infradead.org, hpa@zytor.com, hughd@google.com, ira.weiny@intel.com, isaku.yamahata@intel.com, jack@suse.cz, james.morse@arm.com, jarkko@kernel.org, jgg@ziepe.ca, jgowans@amazon.com, jhubbard@nvidia.com, jthoughton@google.com, jun.miao@intel.com, kai.huang@intel.com, keirf@google.com, kent.overstreet@linux.dev, liam.merwick@oracle.com, maciej.wieczor-retman@intel.com, mail@maciej.szmigiero.name, maobibo@loongson.cn, mathieu.desnoyers@efficios.com, maz@kernel.org, mhiramat@kernel.org, mhocko@kernel.org, mic@digikod.net, michael.roth@amd.com, mingo@redhat.com, mlevitsk@redhat.com, mpe@ellerman.id.au, muchun.song@linux.dev, nikunj@amd.com, nsaenz@amazon.es, oliver.upton@linux.dev, palmer@dabbelt.com, pankaj.gupta@amd.com, paul.walmsley@sifive.com, pbonzini@redhat.com, peterx@redhat.com, pgonda@google.com, prsampat@amd.com, pvorel@suse.cz, qperret@google.com, richard.weiyang@gmail.com, rick.p.edgecombe@intel.com, rientjes@google.com, rostedt@goodmis.org, roypat@amazon.co.uk, rppt@kernel.org, seanjc@google.com, shakeel.butt@linux.dev, shuah@kernel.org, suzuki.poulose@arm.com, tabba@google.com, tglx@linutronix.de, thomas.lendacky@amd.com, vannapurve@google.com, vbabka@suse.cz, viro@zeniv.linux.org.uk, vkuznets@redhat.com, will@kernel.org, willy@infradead.org, wyihan@google.com, xiaoyao.li@intel.com, yan.y.zhao@intel.com, yilun.xu@intel.com, yuzenghui@huawei.com Content-Type: text/plain; charset="UTF-8" Ackerley Tng writes: Found another issue with KVM_CAP_MEMORY_ATTRIBUTES2. KVM_CAP_MEMORY_ATTRIBUTES2 was defined to do the same thing as KVM_CAP_MEMORY_ATTRIBUTES, but that's wrong since KVM_CAP_MEMORY_ATTRIBUTES2 should indicate the presence of KVM_SET_MEMORY_ATTRIBUTES2 and struct kvm_memory_attributes2. Usage is kind of weird and I hope to get feedback on this as well. This describes the difference between the previous version of this patch and the one attached below. I also added this to the changelog Add KVM_CAP_MEMORY_ATTRIBUTES2 to indicate that struct kvm_memory_attributes2 exists and can be used either with KVM_SET_MEMORY_ATTRIBUTES2 via the vm or guest_memfd ioctl. Since KVM_SET_MEMORY_ATTRIBUTES2 is not limited to be used only with the vm ioctl, return 1 for KVM_CAP_MEMORY_ATTRIBUTES2 as long as struct kvm_memory_attributes2 and KVM_SET_MEMORY_ATTRIBUTES2 can be used. KVM_CAP_MEMORY_ATTRIBUTES must still be used to actually get valid attributes. Handle KVM_CAP_MEMORY_ATTRIBUTES2 and return 1 regardless of CONFIG_KVM_VM_MEMORY_ATTRIBUTES, since KVM_SET_MEMORY_ATTRIBUTES2 is not limited to a vm ioctl and can also be used with the guest_memfd ioctl. Here's the entire patch so hopefully it's easy to swap out this entire patch over the original one. >From 8887ba58f6fd97c529c8152d6f18e5e26651dbec Mon Sep 17 00:00:00 2001 From: Ackerley Tng Date: Thu, 16 Oct 2025 11:48:01 -0700 Subject: [PATCH] KVM: Introduce KVM_SET_MEMORY_ATTRIBUTES2 Introduce a "version 2" of KVM_SET_MEMORY_ATTRIBUTES to support returning information back to userspace. This new ioctl and structure will, in a later patch, be shared as a guest_memfd ioctl, where the padding in the new kvm_memory_attributes2 structure will be for writing the response from the guest_memfd ioctl to userspace. A new ioctl is necessary for these reasons: 1. KVM_SET_MEMORY_ATTRIBUTES is currently a write-only ioctl and does not allow userspace to read fields. There's nothing in code (yet?) that validates this, but using _IOWR for consistency would be prudent. 2. KVM_SET_MEMORY_ATTRIBUTES, when used as a guest_memfd ioctl, will need an additional field to provide userspace with more error details. Alternatively, a completely new ioctl could be defined, unrelated to KVM_SET_MEMORY_ATTRIBUTES, but using the same ioctl number and struct for the vm and guest_memfd ioctls streamlines the interface for userspace. In addition, any memory attributes, implemented on the vm or guest_memfd ioctl, can be easily shared with the other. Add KVM_CAP_MEMORY_ATTRIBUTES2 to indicate that struct kvm_memory_attributes2 exists and can be used either with KVM_SET_MEMORY_ATTRIBUTES2 via the vm or guest_memfd ioctl. Since KVM_SET_MEMORY_ATTRIBUTES2 is not limited to be used only with the vm ioctl, return 1 for KVM_CAP_MEMORY_ATTRIBUTES2 as long as struct kvm_memory_attributes2 and KVM_SET_MEMORY_ATTRIBUTES2 can be used. KVM_CAP_MEMORY_ATTRIBUTES must still be used to actually get valid attributes. Handle KVM_CAP_MEMORY_ATTRIBUTES2 and return 1 regardless of CONFIG_KVM_VM_MEMORY_ATTRIBUTES, since KVM_SET_MEMORY_ATTRIBUTES2 is not limited to a vm ioctl and can also be used with the guest_memfd ioctl. Suggested-by: Sean Christopherson Change-Id: I50cd506d9a28bf68a90e659015603de579569bc1 Signed-off-by: Ackerley Tng --- Documentation/virt/kvm/api.rst | 32 ++++++++++++++++++++++++++++++++ include/uapi/linux/kvm.h | 12 ++++++++++++ virt/kvm/kvm_main.c | 34 +++++++++++++++++++++++++++++++--- 3 files changed, 75 insertions(+), 3 deletions(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 754b662a453c3..a812769d79bf6 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -6355,6 +6355,8 @@ S390: Returns -EINVAL if the VM has the KVM_VM_S390_UCONTROL flag set. Returns -EINVAL if called on a protected VM. +.. _KVM_SET_MEMORY_ATTRIBUTES: + 4.141 KVM_SET_MEMORY_ATTRIBUTES ------------------------------- @@ -6512,6 +6514,36 @@ the capability to be present. `flags` must currently be zero. +4.144 KVM_SET_MEMORY_ATTRIBUTES2 +--------------------------------- + +:Capability: KVM_CAP_MEMORY_ATTRIBUTES2 +:Architectures: x86 +:Type: vm ioctl +:Parameters: struct kvm_memory_attributes2 (in/out) +:Returns: 0 on success, <0 on error + +KVM_SET_MEMORY_ATTRIBUTES2 is an extension to +KVM_SET_MEMORY_ATTRIBUTES that supports returning (writing) values to +userspace. The original (pre-extension) fields are shared with +KVM_SET_MEMORY_ATTRIBUTES identically. + +Attribute values are shared with KVM_SET_MEMORY_ATTRIBUTES. + +:: + + struct kvm_memory_attributes2 { + __u64 address; + __u64 size; + __u64 attributes; + __u64 flags; + __u64 reserved[4]; + }; + + #define KVM_MEMORY_ATTRIBUTE_PRIVATE (1ULL << 3) + +See also: :ref: `KVM_SET_MEMORY_ATTRIBUTES`. + .. _kvm_run: diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 52f6000ab0208..c300e38c7c9cd 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -963,6 +963,7 @@ struct kvm_enable_cap { #define KVM_CAP_RISCV_MP_STATE_RESET 242 #define KVM_CAP_ARM_CACHEABLE_PFNMAP_SUPPORTED 243 #define KVM_CAP_GUEST_MEMFD_FLAGS 244 +#define KVM_CAP_MEMORY_ATTRIBUTES2 245 struct kvm_irq_routing_irqchip { __u32 irqchip; @@ -1617,4 +1618,15 @@ struct kvm_pre_fault_memory { __u64 padding[5]; }; +/* Available with KVM_CAP_MEMORY_ATTRIBUTES2 */ +#define KVM_SET_MEMORY_ATTRIBUTES2 _IOWR(KVMIO, 0xd6, struct kvm_memory_attributes2) + +struct kvm_memory_attributes2 { + __u64 address; + __u64 size; + __u64 attributes; + __u64 flags; + __u64 reserved[4]; +}; + #endif /* __LINUX_KVM_H */ diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 35166754a22b4..d083011744eba 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2621,7 +2621,7 @@ static int kvm_vm_set_mem_attributes(struct kvm *kvm, gfn_t start, gfn_t end, return r; } static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm, - struct kvm_memory_attributes *attrs) + struct kvm_memory_attributes2 *attrs) { gfn_t start, end; @@ -4957,6 +4957,7 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg) case KVM_CAP_BINARY_STATS_FD: case KVM_CAP_SYSTEM_EVENT_DATA: case KVM_CAP_DEVICE_CTRL: + case KVM_CAP_MEMORY_ATTRIBUTES2: return 1; #ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES case KVM_CAP_MEMORY_ATTRIBUTES: @@ -5184,6 +5185,14 @@ do { \ sizeof_field(struct kvm_userspace_memory_region2, field)); \ } while (0) +#define SANITY_CHECK_MEMORY_ATTRIBUTES_FIELD(field) \ +do { \ + BUILD_BUG_ON(offsetof(struct kvm_memory_attributes, field) != \ + offsetof(struct kvm_memory_attributes2, field)); \ + BUILD_BUG_ON(sizeof_field(struct kvm_memory_attributes, field) != \ + sizeof_field(struct kvm_memory_attributes2, field)); \ +} while (0) + static long kvm_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg) { @@ -5366,15 +5375,34 @@ static long kvm_vm_ioctl(struct file *filp, } #endif /* CONFIG_HAVE_KVM_IRQ_ROUTING */ #ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES + case KVM_SET_MEMORY_ATTRIBUTES2: case KVM_SET_MEMORY_ATTRIBUTES: { - struct kvm_memory_attributes attrs; + struct kvm_memory_attributes2 attrs; + unsigned long size; + + if (ioctl == KVM_SET_MEMORY_ATTRIBUTES) { + /* + * Fields beyond struct kvm_userspace_memory_region shouldn't be + * accessed, but avoid leaking kernel memory in case of a bug. + */ + memset(&attrs, 0, sizeof(attrs)); + size = sizeof(struct kvm_memory_attributes); + } else { + size = sizeof(struct kvm_memory_attributes2); + } + + /* Ensure the common parts of the two structs are identical. */ + SANITY_CHECK_MEMORY_ATTRIBUTES_FIELD(address); + SANITY_CHECK_MEMORY_ATTRIBUTES_FIELD(size); + SANITY_CHECK_MEMORY_ATTRIBUTES_FIELD(attributes); + SANITY_CHECK_MEMORY_ATTRIBUTES_FIELD(flags); r = -ENOTTY; if (!vm_memory_attributes) goto out; r = -EFAULT; - if (copy_from_user(&attrs, argp, sizeof(attrs))) + if (copy_from_user(&attrs, argp, size)) goto out; r = kvm_vm_ioctl_set_mem_attributes(kvm, &attrs); -- 2.51.1.838.g19442a804e-goog