On Wed, Jul 26, 2023, Federico Parola wrote: > On 7/26/23 10:31, Sean Christopherson wrote: > > On Wed, Jul 26, 2023, Federico Parola wrote: > > > Hi everyone, > > > is it possible to pre-populate the TDP table (EPT in my case) when > > > configuring the VM environment, so that there won't be a page fault / VM > > > exit every time the guest tries to access a RAM page for the first time? > > > > No, not yet. > > > > > At the moment I see a lot of page faults when the VM boots, is it possible > > > to prevent them to reduce boot time? > > > > You can't currently prevent the page faults, but you can _significantly_ reduce > > them by backing guest memory with hugepages. E.g. using 2MiB instead of 4KiB > > pages reduces the number of faults by 512x, and 1GiB (HugeTLB only) instead of > > 2MiB by another 512x. > > > > But the word yet... > > > > KVM needs to add internal APIs to allow userspace to tell to KVM map a particular > > GPA in order to support upcoming flavors of confidential VMs[1]. I could have > > sworn that I requested that that API be exposed to userspace via a common ioctl(), > > e.g. so that userspace can prefault all of guest memory if userspace is so inclined. > > Ah, I only made that comment in passing[2]. > > > > I'll follow-up in the TDX series to "officially" float the idea of exposing the > > helper as an ioctl(). > > > > [1] https://lkml.kernel.org/r/6a4c029af70d41b63bcee3d6a1f0c2377f6eb4bd.1690322424.git.isaku.yamahata%40intel.com > > [2] https://lore.kernel.org/all/ZGuh1J6AOw5v2R1W@xxxxxxxxxx > > Thank you very much for the prompt reply and useful tips. I'll keep an eye > on the topic. FYI, I finally followed through on this. https://lore.kernel.org/all/Zbrj5WKVgMsUFDtb@xxxxxxxxxx
