Re: [PATCH v6 0/6] x86/tdx: Allow MMIO instructions from userspace

[Dave Hansen]

On 9/6/24 04:49, Alexey Gladkov wrote:
> Currently, MMIO inside the TDX guest is allowed from kernel space and access
> from userspace is denied. This becomes a problem when working with virtual
> devices in userspace.

Kernel MMIO and User MMIO are very different beasts.

The kernel MMIO instructions are trusted and can be constrained to use a
very limited number of instructions that match the kernel's limited
instruction decoding capability.

Userspace is not constrained in that way.

TDX also doesn't have the option of having the VMM deal with the
instruction emulation.

Before we start down this road, I'd really want to hear from the KVM
folks that having the kernel decode arbitrary user instructions is the
way we want to go.