Re: [RFC PATCH v11 12/29] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory

[Vishal Annapurve]

On Tue, Jul 18, 2023 at 4:49 PM Sean Christopherson <seanjc@xxxxxxxxxx> 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;
> +}
> +