Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx> writes: > In confidential computing usages, whether a page is private or shared is > necessary information for KVM to perform operations like page fault > handling, page zapping etc. There are other potential use cases for > per-page memory attributes, e.g. to make memory read-only (or no-exec, > or exec-only, etc.) without having to modify memslots. > > Introduce two ioctls (advertised by KVM_CAP_MEMORY_ATTRIBUTES) to allow > userspace to operate on the per-page memory attributes. > - KVM_SET_MEMORY_ATTRIBUTES to set the per-page memory attributes to > a guest memory range. > - KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to return the KVM supported > memory attributes. > > KVM internally uses xarray to store the per-page memory attributes. > > Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx> > Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx> > Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@xxxxxxxxxx/ > --- > Documentation/virt/kvm/api.rst | 63 ++++++++++++++++++++++++++++ > arch/x86/kvm/Kconfig | 1 + > include/linux/kvm_host.h | 3 ++ > include/uapi/linux/kvm.h | 17 ++++++++ > virt/kvm/Kconfig | 3 ++ > virt/kvm/kvm_main.c | 76 ++++++++++++++++++++++++++++++++++ > 6 files changed, 163 insertions(+) > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > index 5617bc4f899f..bb2f709c0900 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst > @@ -5952,6 +5952,59 @@ delivery must be provided via the "reg_aen" struct. > The "pad" and "reserved" fields may be used for future extensions and should be > set to 0s by userspace. > > +4.138 KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES > +----------------------------------------- > + > +:Capability: KVM_CAP_MEMORY_ATTRIBUTES > +:Architectures: x86 > +:Type: vm ioctl > +:Parameters: u64 memory attributes bitmask(out) > +:Returns: 0 on success, <0 on error > + > +Returns supported memory attributes bitmask. Supported memory attributes will > +have the corresponding bits set in u64 memory attributes bitmask. > + > +The following memory attributes are defined:: > + > + #define KVM_MEMORY_ATTRIBUTE_READ (1ULL << 0) > + #define KVM_MEMORY_ATTRIBUTE_WRITE (1ULL << 1) > + #define KVM_MEMORY_ATTRIBUTE_EXECUTE (1ULL << 2) > + #define KVM_MEMORY_ATTRIBUTE_PRIVATE (1ULL << 3) > + > +4.139 KVM_SET_MEMORY_ATTRIBUTES > +----------------------------------------- > + > +:Capability: KVM_CAP_MEMORY_ATTRIBUTES > +:Architectures: x86 > +:Type: vm ioctl > +:Parameters: struct kvm_memory_attributes(in/out) > +:Returns: 0 on success, <0 on error > + > +Sets memory attributes for pages in a guest memory range. Parameters are > +specified via the following structure:: > + > + struct kvm_memory_attributes { > + __u64 address; > + __u64 size; > + __u64 attributes; > + __u64 flags; > + }; > + > +The user sets the per-page memory attributes to a guest memory range indicated > +by address/size, and in return KVM adjusts address and size to reflect the > +actual pages of the memory range have been successfully set to the attributes. This wording could cause some confusion, what about a simpler: "reflect the range of pages that had its attributes successfully set" > +If the call returns 0, "address" is updated to the last successful address + 1 > +and "size" is updated to the remaining address size that has not been set > +successfully. "address + 1 page" or "subsequent page" perhaps. In fact, wouldn't this all become simpler if size were number of pages instead? > The user should check the return value as well as the size to > +decide if the operation succeeded for the whole range or not. The user may want > +to retry the operation with the returned address/size if the previous range was > +partially successful. > + > +Both address and size should be page aligned and the supported attributes can be > +retrieved with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES. > + > +The "flags" field may be used for future extensions and should be set to 0s. > + ... > +static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm, > + struct kvm_memory_attributes *attrs) > +{ > + gfn_t start, end; > + unsigned long i; > + void *entry; > + u64 supported_attrs = kvm_supported_mem_attributes(kvm); > + > + /* flags is currently not used. */ > + if (attrs->flags) > + return -EINVAL; > + if (attrs->attributes & ~supported_attrs) > + return -EINVAL; > + if (attrs->size == 0 || attrs->address + attrs->size < attrs->address) > + return -EINVAL; > + if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size)) > + return -EINVAL; > + > + start = attrs->address >> PAGE_SHIFT; > + end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT; Here PAGE_SIZE and -1 cancel out. Consider using gpa_to_gfn as well. > + > + entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL; > + > + mutex_lock(&kvm->lock); > + for (i = start; i < end; i++) > + if (xa_err(xa_store(&kvm->mem_attr_array, i, entry, > + GFP_KERNEL_ACCOUNT))) > + break; > + mutex_unlock(&kvm->lock); > + > + attrs->address = i << PAGE_SHIFT; > + attrs->size = (end - i) << PAGE_SHIFT; > + > + return 0; > +} > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */ > + > struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn) > { > return __gfn_to_memslot(kvm_memslots(kvm), gfn); > @@ -4459,6 +4508,9 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg) > #ifdef CONFIG_HAVE_KVM_MSI > case KVM_CAP_SIGNAL_MSI: > #endif > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES > + case KVM_CAP_MEMORY_ATTRIBUTES: > +#endif > #ifdef CONFIG_HAVE_KVM_IRQFD > case KVM_CAP_IRQFD: > case KVM_CAP_IRQFD_RESAMPLE: > @@ -4804,6 +4856,30 @@ static long kvm_vm_ioctl(struct file *filp, > break; > } > #endif /* CONFIG_HAVE_KVM_IRQ_ROUTING */ > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES > + case KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES: { > + u64 attrs = kvm_supported_mem_attributes(kvm); > + > + r = -EFAULT; > + if (copy_to_user(argp, &attrs, sizeof(attrs))) > + goto out; > + r = 0; > + break; > + } > + case KVM_SET_MEMORY_ATTRIBUTES: { > + struct kvm_memory_attributes attrs; > + > + r = -EFAULT; > + if (copy_from_user(&attrs, argp, sizeof(attrs))) > + goto out; > + > + r = kvm_vm_ioctl_set_mem_attributes(kvm, &attrs); > + > + if (!r && copy_to_user(argp, &attrs, sizeof(attrs))) > + r = -EFAULT; > + break; > + } > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */ > case KVM_CREATE_DEVICE: { > struct kvm_create_device cd;
