On Tue, 2023-07-04 at 18:58 +0200, Peter Zijlstra wrote: > On Fri, Jun 30, 2023 at 02:24:56PM -0700, Sean Christopherson wrote: > > > Waiting until userspace attempts to create the first TDX guest adds complexity > > and limits what KVM can do to harden itself. Currently, all feature support in > > KVM is effectively frozen at module load. E.g. most of the setup code is > > contained in __init functions, many module-scoped variables are effectively > > RO after init (though they can't be marked as such until we smush kvm-intel.ko > > and kvm-amd.ko into kvm.ko, which is tentatively the long-term plan). All of > > those patterns would get tossed aside if KVM waits until userspace attempts to > > create the first guest. > > .... > > People got poked and the following was suggested: > > On boot do: > > TDH.SYS.INIT > TDH.SYS.LP.INIT > TDH.SYS.CONFIG > TDH.SYS.KEY.CONFIG > > This should get TDX mostly sorted, but doesn't consume much resources. > Then later, when starting the first TDX guest, do the whole > > TDH.TDMR.INIT > > dance to set up the PAMT array -- which is what gobbles up memory. From > what I understand the TDH.TDMR.INIT thing is not one of those > excessively long calls. The TDH.TDMR.INIT itself has it's own latency requirement implemented in the TDX module, thus it only initializes a small chunk (1M I guess) in each call. Therefore we need a loop to do bunch of TDH.TDMR.INIT in order to initialize all PAMT entries for all TDX-usable memory, which can be time-consuming. Currently for simplicity we just do this inside the module initialization, but can be optimized later when we have an agreed solution of how to optimize. > > If we have concerns about allocating the PAMT array, can't we use CMA > for this? Allocate the whole thing at boot as CMA such that when not > used for TDX it can be used for regular things like userspace and > filecache pages? The PAMT allocation itself isn't a concern I think. The concern is the TDH.TDMR.INIT to initialize them. Also, one practical problem to prevent us from pre-allocating PAMT is the PAMT size to be allocated can only be determined after the TDH.SYS.INFO SEAMCALL, which reports the "PAMT entry size" in the TDSYSINFO_STRUCT. > > Those TDH.SYS calls should be enough to ensure TDX is actually working, > no?
