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SubjectRe: [RFC v1 05/26] x86/traps: Add #VE support for TDX guest
On Fri, Feb 12, 2021, Andy Lutomirski wrote:
> On Fri, Feb 5, 2021 at 3:39 PM Kuppuswamy Sathyanarayanan
> <sathyanarayanan.kuppuswamy@linux.intel.com> wrote:
> >
> > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> >
> > 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.

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