Although the KVM API says that a write to a RO memslot must result in a KVM_EXIT_MMIO describing the write, the arm64 architecture doesn't provide the *data* written by a Stage-1 page table walk (we only get the address). Since there isn't much userspace can do with so little information anyway, document the fact that such an access results in a guest exception, not an exit. This is consistent with the guest being terminally broken anyway. Reviewed-by: Oliver Upton <oliver.upton@xxxxxxxxx> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx> --- Documentation/virt/kvm/api.rst | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 0dd5d8733dd5..42db72a0cbe6 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -1354,6 +1354,14 @@ the memory region are automatically reflected into the guest. For example, an mmap() that affects the region will be made visible immediately. Another example is madvise(MADV_DROP). +Note: On arm64, a write generated by the page-table walker (to update +the Access and Dirty flags, for example) never results in a +KVM_EXIT_MMIO exit when the slot has the KVM_MEM_READONLY flag. This +is because KVM cannot provide the data that would be written by the +page-table walker, making it impossible to emulate the access. +Instead, an abort (data abort if the cause of the page-table update +was a load or a store, instruction abort if it was an instruction +fetch) is injected in the guest. 4.36 KVM_SET_TSS_ADDR --------------------- -- 2.34.1
