On 4/14/26 01:43, Michael S. Tsirkin wrote: > On Mon, Apr 13, 2026 at 06:06:14PM -0400, Michael S. Tsirkin wrote: >> On Mon, Apr 13, 2026 at 11:05:40AM +0200, David Hildenbrand (Arm) wrote: >> >> ... >> >>> (2) Use a dedicated allocation interface for user pages in the buddy. >>> >>> I hate the whole user_alloc_needs_zeroing()+folio_zero_user() handling. >>> >>> It shouldn't exist. We should just be passing GFP_ZERO and let the buddy >>> handle >>> all that. >>> >>> >>> For example, vma_alloc_folio() already gets passed the address in. >>> >>> Pass the address from vma_alloc_folio_noprof()->folio_alloc_noprof(), and >>> let >>> folio_alloc_noprof() use a buddy interface that can handle it. >>> >>> Imagine if we had a alloc_user_pages_noprof() that consumes an address. It >>> could just >>> do what folio_zero_user() does, and only if really required. >>> >>> The whole user_alloc_needs_zeroing() could go away and you could just >>> handle the >>> pre-zeroed optimization internally. >> >> I looked at this a bit, and I think the issue is that the buddy >> allocator doesn't do the arch-specific cache handling. >> So allocating it is a fundamentally different thing from GFP_ZERO which >> is "zero a kernel address range". >> >> So I don't get how you want to do it. >
Saw your new mails just now. > Oh, wait, do you mean we thread the userspace address through all the > allocation calls? > Like the below? This is on top of my patches, on top of mm it will be > a tiny bit smaller. I can rebase no problem. > > But: isn't it a bit overkill for something that is, in the end, > virtualization specific? > It's all mechanical threading through of user_addr, but should we miss > one place, and suddenly you get weird corruption on esoteric arches > since we will get memset instead of folio_zero_user. > > Worth it? See my other mail, we'd be forwarding it only for vma_alloc_folio_noprof(), where we call a _user specific interface. Then we can get rid of the user_alloc_needs_zeroing() hack and just do the right thing in page_alloc.c -- Cheers, David
