On Fri, Feb 12, 2021 at 1:37 PM Sean Christopherson <[email protected]> wrote: > > On Fri, Feb 12, 2021, Dave Hansen wrote: > > On 2/12/21 12:54 PM, Sean Christopherson wrote: > > > Ah, I see what you're thinking. > > > > > > Treating an EPT #VE as fatal was also considered as an option. IIUC it > > > was > > > thought that finding every nook and cranny that could access a page, > > > without > > > forcing the kernel to pre-accept huge swaths of memory, would be very > > > difficult. > > > It'd be wonderful if that's not the case. > > > > We have to manually set up the page table entries for every physical > > page of memory (except for the hard-coded early stuff below 8MB or > > whatever). We *KNOW*, 100% before physical memory is accessed. > > > > There aren't nooks and crannies where memory is accessed. There are a > > few, very well-defined choke points which must be crossed before memory > > is accessed. Page table creation, bootmem and the core page allocator > > come to mind. > > Heh, for me, that's two places too many beyond my knowledge domain to feel > comfortable putting a stake in the ground saying #VE isn't necessary. > > Joking aside, I agree that treating EPT #VEs as fatal would be ideal, but > from a > TDX architecture perspective, when considering all possible kernels, drivers, > configurations, etc..., it's risky to say that there will _never_ be a > scenario > that "requires" #VE. > > What about adding a property to the TD, e.g. via a flag set during TD > creation, > that controls whether unaccepted accesses cause #VE or are, for all intents > and > purposes, fatal? That would allow Linux to pursue treating EPT #VEs for > private > GPAs as fatal, but would give us a safety and not prevent others from > utilizing > #VEs.
That seems reasonable.
