Re: [RFC 32/33] KVM: x86: hyper-v: Implement HVCALL_TRANSLATE_VIRTUAL_ADDRESS

[Nicolas Saenz Julienne]

On Wed Nov 8, 2023 at 12:49 PM UTC, Alexander Graf wrote:
>
> On 08.11.23 12:18, Nicolas Saenz Julienne wrote:
> > Introduce HVCALL_TRANSLATE_VIRTUAL_ADDRESS, the hypercall receives a
> > GVA, generally from a less privileged VTL, and returns the GPA backing
> > it. The GVA -> GPA conversion is done by walking the target VTL's vCPU
> > MMU.
> >
> > NOTE: The hypercall implementation is incomplete and only shared for
> > completion. Additionally we'd like to move the VTL aware parts to
> > user-space.
>
>
> Yes, please :). We should handle the complete hypercall in user space if 
> possible. If you're afraid that gva -> gpa conversion may run out of 
> sync between a user space and the kvm implementations, let's introduce 
> an ioctl that allows you to perform that conversion.

I'll look into introducing a generic API that performs MMU walks. The
devil is in the details though, the hypercall introduces flags like:

• HV_TRANSLATE_GVA_TLB_FLUSH_INHIBIT: Indicates that the TlbFlushInhibit
  flag in the virtual processor’s HvRegisterInterceptSuspend register
  should be set as a consequence of a successful return. This prevents
  other virtual processors associated with the target partition from
  flushing the stage 1 TLB of the specified virtual processor until
  after the TlbFlushInhibit flag is cleared.

Which make things trickier.

Nicolas