On Thu, Mar 09, 2023, Mike Rapoport wrote: > On Thu, Mar 09, 2023 at 01:59:00AM +0000, Edgecombe, Rick P wrote: > > On Wed, 2023-03-08 at 11:41 +0200, Mike Rapoport wrote: > > > From: "Mike Rapoport (IBM)" <rppt@xxxxxxxxxx> > > > > > > Hi, > > > > > > This is a third attempt to make page allocator aware of the direct > > > map > > > layout and allow grouping of the pages that must be unmapped from > > > the direct map. > > > > > > This a new implementation of __GFP_UNMAPPED, kinda a follow up for > > > this set: > > > > > > https://lore.kernel.org/all/20220127085608.306306-1-rppt@xxxxxxxxxx > > > > > > but instead of using a migrate type to cache the unmapped pages, the > > > current implementation adds a dedicated cache to serve __GFP_UNMAPPED > > > allocations. > > > > It seems a downside to having a page allocator outside of _the_ page > > allocator is you don't get all of the features that are baked in there. > > For example does secretmem care about numa? I guess in this > > implementation there is just one big cache for all nodes. > > > > Probably most users would want __GFP_ZERO. Would secretmem care about > > __GFP_ACCOUNT? > > The intention was that the pages in cache are always zeroed, so __GFP_ZERO > is always implicitly there, at least should have been. Would it be possible to drop that assumption/requirement, i.e. allow allocation of __GFP_UNMAPPED without __GFP_ZERO? At a glance, __GFP_UNMAPPED looks like it would be a great fit for backing guest memory, in particular for confidential VMs. And for some flavors of CoCo, i.e. TDX, the trusted intermediary is responsible for zeroing/initializing guest memory as the untrusted host (kernel/KVM) doesn't have access to the guest's encryption key. In other words, zeroing in the kernel would be unnecessary work.
