On 20.02.20 11:39, Christian Borntraeger wrote: > From: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx> > > With the introduction of protected KVM guests on s390 there is now a > concept of inaccessible pages. These pages need to be made accessible > before the host can access them. > > While cpu accesses will trigger a fault that can be resolved, I/O > accesses will just fail. We need to add a callback into architecture > code for places that will do I/O, namely when writeback is started or > when a page reference is taken. > > This is not only to enable paging, file backing etc, it is also > necessary to protect the host against a malicious user space. For > example a bad QEMU could simply start direct I/O on such protected > memory. We do not want userspace to be able to trigger I/O errors and > thus we the logic is "whenever somebody accesses that page (gup) or > doing I/O, make sure that this page can be accessed. When the guest > tries to access that page we will wait in the page fault handler for > writeback to have finished and for the page_ref to be the expected > value. Subject: "mm: gup..." And I'd probably add that on s390x, it's unlikely to ever return !0. (why the WARN_ON is okay and has to be tackled once relevant) > > Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx> > Acked-by: Will Deacon <will@xxxxxxxxxx> > Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> -- Thanks, David / dhildenb
