On Thu, 2024-05-16 at 10:34 +1200, Huang, Kai wrote: > > > On 15/05/2024 12:59 pm, Rick Edgecombe wrote: > > From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx> > > > > Introduce a "gfn_shared_mask" field in the kvm_arch structure to record GPA > > shared bit and provide address conversion helpers for TDX shared bit of > > GPA. > > > > TDX designates a specific GPA bit as the shared bit, which can be either > > bit 51 or bit 47 based on configuration. > > > > This GPA shared bit indicates whether the corresponding physical page is > > shared (if shared bit set) or private (if shared bit cleared). > > > > - GPAs with shared bit set will be mapped by VMM into conventional EPT, > > which is pointed by shared EPTP in TDVMCS, resides in host VMM memory > > and is managed by VMM. > > - GPAs with shared bit cleared will be mapped by VMM firstly into a > > mirrored EPT, which resides in host VMM memory. Changes of the mirrored > > EPT are then propagated into a private EPT, which resides outside of > > host > > VMM memory and is managed by TDX module. > > > > Add the "gfn_shared_mask" field to the kvm_arch structure for each VM with > > a default value of 0. It will be set to the position of the GPA shared bit > > in GFN through TD specific initialization code. > > > > Provide helpers to utilize the gfn_shared_mask to determine whether a GPA > > is shared or private, retrieve the GPA shared bit value, and insert/strip > > shared bit to/from a GPA. > > I am seriously thinking whether we should just abandon this whole > kvm_gfn_shared_mask() thing. > > We already have enough mechanisms around private memory and the mapping > of it: > > 1) Xarray to query whether a given GFN is private or shared; > 2) fault->is_private to indicate whether a faulting address is private > or shared; > 3) sp->is_private to indicate whether a "page table" is only for private > mapping; You mean drop the helpers, or the struct kvm member? I think we still need the shared bit position stored somewhere. memslots, Xarray, etc need to operate on the GFN without the shared it.
