On Mon, May 05, 2025, Vishal Annapurve wrote: > On Mon, May 5, 2025 at 10:17 PM Vishal Annapurve <vannapurve@xxxxxxxxxx> wrote: > > > > On Mon, May 5, 2025 at 3:57 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > > > ... > > > > And not worry about lpage_infor for the time being, until we actually do > > > > support larger pages. > > > > > > I don't want to completely punt on this, because if it gets messy, then I want > > > to know now and have a solution in hand, not find out N months from now. > > > > > > That said, I don't expect it to be difficult. What we could punt on is > > > performance of the lookups, which is the real reason KVM maintains the rather > > > expensive disallow_lpage array. > > > > > > And that said, memslots can only bind to one guest_memfd instance, so I don't > > > immediately see any reason why the guest_memfd ioctl() couldn't process the > > > slots that are bound to it. I.e. why not update KVM_LPAGE_MIXED_FLAG from the > > > guest_memfd ioctl() instead of from KVM_SET_MEMORY_ATTRIBUTES? > > > > I am missing the point here to update KVM_LPAGE_MIXED_FLAG for the > > scenarios where in-place memory conversion will be supported with > > guest_memfd. As guest_memfd support for hugepages comes with the > > design that hugepages can't have mixed attributes. i.e. max_order > > returned by get_pfn will always have the same attributes for the folio > > range. Oh, if this will naturally be handled by guest_memfd, then do that. I was purely reacting to David's suggestion to "not worry about lpage_infor for the time being, until we actually do support larger pages". > > Is your suggestion around using guest_memfd ioctl() to also toggle > > memory attributes for the scenarios where guest_memfd instance doesn't > > have in-place memory conversion feature enabled? > > Reading more into your response, I guess your suggestion is about > covering different usecases present today and new usecases which may > land in future, that rely on kvm_lpage_info for faster lookup. If so, > then it should be easy to modify guest_memfd ioctl to update > kvm_lpage_info as you suggested. Nah, I just missed/forgot that using a single guest_memfd for private and shared would naturally need to split the folio and thus this would Just Work.
