On Mon, Oct 30, 2023, Chao Gao wrote:
> On Fri, Oct 27, 2023 at 11:21:55AM -0700, Sean Christopherson wrote:
> >From: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> >
> >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.
>
> This ioctl() is already removed. So, the changelog is out-of-date and needs
> an update.
Doh, I lost track of this and the fixup for KVM_CAP_MEMORY_ATTRIBUTES below.
> >+:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> >+:Architectures: x86
> >+:Type: vm ioctl
> >+:Parameters: struct kvm_memory_attributes(in)
>
> ^ add one space here?
Ah, yeah, that does appear to be the standard.
>
>
> >+static bool kvm_pre_set_memory_attributes(struct kvm *kvm,
> >+ struct kvm_gfn_range *range)
> >+{
> >+ /*
> >+ * Unconditionally add the range to the invalidation set, regardless of
> >+ * whether or not the arch callback actually needs to zap SPTEs. E.g.
> >+ * if KVM supports RWX attributes in the future and the attributes are
> >+ * going from R=>RW, zapping isn't strictly necessary. Unconditionally
> >+ * adding the range allows KVM to require that MMU invalidations add at
> >+ * least one range between begin() and end(), e.g. allows KVM to detect
> >+ * bugs where the add() is missed. Rexlaing the rule *might* be safe,
>
> ^^^^^^^^ Relaxing
>
> >@@ -4640,6 +4850,17 @@ 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:
> > return 1;
> >+#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
> >+ case KVM_CAP_MEMORY_ATTRIBUTES:
> >+ u64 attrs = kvm_supported_mem_attributes(kvm);
> >+
> >+ r = -EFAULT;
> >+ if (copy_to_user(argp, &attrs, sizeof(attrs)))
> >+ goto out;
> >+ r = 0;
> >+ break;
>
> This cannot work, e.g., no @argp in this function and is fixed by a later commit:
>
> fcbef1e5e5d2 ("KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory")
I'll post a fixup patch for all of these, thanks much!
