On Mon, 11 Apr 2022, Kirill A. Shutemov wrote: > On Fri, Apr 08, 2022 at 09:02:54PM +0800, Chao Peng wrote: > > > I think the correct approach is to not do the locking automatically for SHM_F_INACCESSIBLE, > > > and instead require userspace to do shmctl(.., SHM_LOCK, ...) if userspace knows the > > > consumers don't support migrate/swap. That'd require wrapping migrate_page() and then > > > wiring up notifier hooks for migrate/swap, but IMO that's a good thing to get sorted > > > out sooner than later. KVM isn't planning on support migrate/swap for TDX or SNP, > > > but supporting at least migrate for a software-only implementation a la pKVM should > > > be relatively straightforward. On the notifiee side, KVM can terminate the VM if it > > > gets an unexpected migrate/swap, e.g. so that TDX/SEV VMs don't die later with > > > exceptions and/or data corruption (pre-SNP SEV guests) in the guest. > > > > SHM_LOCK sounds like a good match. > > Emm, no. shmctl(2) and SHM_LOCK are SysV IPC thing. I don't see how they > fit here. I am still struggling to formulate a constructive response on MFD_INACCESSIBLE in general: but before doing so, let me jump in here to say that I'm firmly on the side of SHM_LOCK being the right model - but admittedly not through userspace calling shmctl(2). Please refer to our last year's posting "[PATCH 10/16] tmpfs: fcntl(fd, F_MEM_LOCK) to memlock a tmpfs file" for the example of how Shakeel did it then (though only a small part of that would be needed for this case): https://lore.kernel.org/linux-mm/54e03798-d836-ae64-f41-4a1d46bc115b@xxxxxxxxxx/ And until such time as swapping is enabled, this memlock accounting would be necessarily entailed by "MFD_INACCESSIBLE", or however that turns out to be implemented: not something that we could trust userspace to call separately. Hugh
