Re: [RFC PATCH v11 12/29] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory
From: Sean Christopherson <seanjc@google.com>
Date: 2023-07-19 17:47:50
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kvm, kvm-riscv, kvmarm, linux-arm-kernel, linux-fsdevel, linux-mips, linux-mm, linux-riscv, linux-security-module, lkml
On Wed, Jul 19, 2023, Vishal Annapurve wrote:
On Tue, Jul 18, 2023 at 4:49 PM Sean Christopherson [off-list ref] wrote:quoted
... +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.
Hmm, yes, that would be much better. Ah, and kvm_gmem_get_pfn() needs to check folio_test_hwpoison() and potentially PageHWPoison(). E.g. if the folio is huge, KVM needs to restrict the mapping to order-0 (target page isn't poisoned), or return KVM_PFN_ERR_HWPOISON (taget page IS poisoned). Alternatively, KVM could punch a hole in kvm_gmem_error_page(), but I don't think we want to do that because that would prevent forwarding the #MC to the guest.