On Fri, May 19, 2023 at 08:40:48AM -0700, Sean Christopherson wrote: > 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. Making and unmapped allocation without __GFP_ZERO shouldn't be a problem. However, using a gfp flag and hooking up into the free path in page allocator have issues and preferably should be avoided. Will something like unmapped_alloc() and unmapped_free() work for your usecase? -- Sincerely yours, Mike.
