> On Feb 12, 2021, at 12:06 PM, Sean Christopherson <[email protected]> wrote: > > On Fri, Feb 12, 2021, Andy Lutomirski wrote: >>> On Fri, Feb 5, 2021 at 3:39 PM Kuppuswamy Sathyanarayanan >>> <[email protected]> wrote: >>> >>> From: "Kirill A. Shutemov" <[email protected]> >>> >>> The TDX module injects #VE exception to the guest TD in cases of >>> disallowed instructions, disallowed MSR accesses and subset of CPUID >>> leaves. Also, it's theoretically possible for CPU to inject #VE >>> exception on EPT violation, but the TDX module makes sure this does >>> not happen, as long as all memory used is properly accepted using >>> TDCALLs. >> >> By my very cursory reading of the TDX arch specification 9.8.2, >> "Secure" EPT violations don't send #VE. But the docs are quite >> unclear, or at least the docs I found are. > > The version I have also states that SUPPRESS_VE is always set. So either > there > was a change in direction, or the public docs need to be updated. Lazy accept > requires a #VE, either from hardware or from the module. The latter would > require walking the Secure EPT tables on every EPT violation... > >> What happens if the guest attempts to access a secure GPA that is not >> ACCEPTed? For example, suppose the VMM does THH.MEM.PAGE.REMOVE on a secure >> address and the guest accesses it, via instruction fetch or data access. >> What happens? > > Well, as currently written in the spec, it will generate an EPT violation and > the host will have no choice but to kill the guest.
Or page the page back in and try again? In regular virt guests, if the host pages out a guest page, it’s the host’s job to put it back when needed. In paravirt, a well designed async of protocol can sometimes let the guest to useful work when this happens. If a guest (or bare metal) has its memory hot removed (via balloon or whatever) and the kernel messes up and accesses removed memory, the guest (or bare metal) is toast. I don’t see why TDX needs to be any different.
