On 19.08.22 05:38, Hugh Dickins wrote: > On Fri, 19 Aug 2022, Sean Christopherson wrote: >> On Thu, Aug 18, 2022, Kirill A . Shutemov wrote: >>> On Wed, Aug 17, 2022 at 10:40:12PM -0700, Hugh Dickins wrote: >>>> On Wed, 6 Jul 2022, Chao Peng wrote: >>>> But since then, TDX in particular has forced an effort into preventing >>>> (by flags, seals, notifiers) almost everything that makes it shmem/tmpfs. >>>> >>>> Are any of the shmem.c mods useful to existing users of shmem.c? No. >>>> Is MFD_INACCESSIBLE useful or comprehensible to memfd_create() users? No. >> >> But QEMU and other VMMs are users of shmem and memfd. The new features certainly >> aren't useful for _all_ existing users, but I don't think it's fair to say that >> they're not useful for _any_ existing users. > > Okay, I stand corrected: there exist some users of memfd_create() > who will also have use for "INACCESSIBLE" memory. As raised in reply to the relevant patch, I'm not sure if we really have to/want to expose MFD_INACCESSIBLE to user space. I feel like this is a requirement of specific memfd_notifer (memfile_notifier) implementations -- such as TDX that will convert the memory and MCE-kill the machine on ordinary write access. We might be able to set/enforce this when registering a notifier internally instead, and fail notifier registration if a condition isn't met (e.g., existing mmap). So I'd be curious, which other users of shmem/memfd would benefit from (MMU)-"INACCESSIBLE" memory obtained via memfd_create()? -- Thanks, David / dhildenb
