On Tue, Dec 06, 2022 at 10:34:32AM -0300, Fabiano Rosas wrote: > 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" Thanks, this is much better. > > > +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? It indeed becomes better if the size is number of pages and the address is gfn, but I think we don't want to imply that the page size is 4K to userspace. > > > 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. Correct! > > Consider using gpa_to_gfn as well. Yes using gpa_to_gfn is appropriate. Thanks, Chao > > > + > > + 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;
