On Tue, Jul 18, 2023 at 4:49 PM Sean Christopherson [off-list ref] wrote:

...
+static int kvm_gmem_error_page(struct address_space *mapping, struct page *page)
+{
+       struct list_head *gmem_list = &mapping->private_list;
+       struct kvm_memory_slot *slot;
+       struct kvm_gmem *gmem;
+       unsigned long index;
+       pgoff_t start, end;
+       gfn_t gfn;
+
+       filemap_invalidate_lock_shared(mapping);
+
+       start = page->index;
+       end = start + thp_nr_pages(page);
+
+       list_for_each_entry(gmem, gmem_list, entry) {
+               xa_for_each_range(&gmem->bindings, index, slot, start, end - 1) {
+                       for (gfn = start; gfn < end; gfn++) {
+                               if (WARN_ON_ONCE(gfn < slot->base_gfn ||
+                                               gfn >= slot->base_gfn + slot->npages))
+                                       continue;
+
+                               /*
+                                * FIXME: Tell userspace that the *private*
+                                * memory encountered an error.
+                                */
+                               send_sig_mceerr(BUS_MCEERR_AR,
+                                               (void __user *)gfn_to_hva_memslot(slot, gfn),
+                                               PAGE_SHIFT, current);

Does it make sense to replicate what happens with MCE handling on
tmpfs backed guest memory:
1) Unmap gpa from guest
2) On the next guest EPT fault, exit to userspace to handle/log the
mce error for the gpa.

IIUC, such MCEs could be asynchronous and "current" might not always
be the intended recipient of this signal.

+                       }
+               }
+       }
+
+       filemap_invalidate_unlock_shared(mapping);
+
+       return 0;
+}
+