Re: [PATCH v1 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD

[Andy Lutomirski]

> On Mar 26, 2021, at 5:18 PM, Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> wrote:
> 
> In non-root TDX guest mode, MWAIT, MONITOR and WBINVD instructions
> are not supported. So handle #VE due to these instructions as no ops.

These should at least be WARN.

Does TDX send #UD if these instructions have the wrong CPL?  If the #VE came from user mode, we should send an appropriate signal instead.

> 
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> ---
> 
> Changes since previous series:
> * Suppressed MWAIT feature as per Andi's comment.
> * Added warning debug log for MWAIT #VE exception.
> 
> arch/x86/kernel/tdx.c | 23 +++++++++++++++++++++++
> 1 file changed, 23 insertions(+)
> 
> diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
> index e936b2f88bf6..fb7d22b846fc 100644
> --- a/arch/x86/kernel/tdx.c
> +++ b/arch/x86/kernel/tdx.c
> @@ -308,6 +308,9 @@ void __init tdx_early_init(void)
> 
>    setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
> 
> +    /* MWAIT is not supported in TDX platform, so suppress it */
> +    setup_clear_cpu_cap(X86_FEATURE_MWAIT);
> +
>    tdg_get_info();
> 
>    pv_ops.irq.safe_halt = tdg_safe_halt;
> @@ -362,6 +365,26 @@ int tdg_handle_virtualization_exception(struct pt_regs *regs,
>    case EXIT_REASON_EPT_VIOLATION:
>        ve->instr_len = tdg_handle_mmio(regs, ve);
>        break;
> +    /*
> +     * Per Guest-Host-Communication Interface (GHCI) for Intel Trust
> +     * Domain Extensions (Intel TDX) specification, sec 2.4,
> +     * some instructions that unconditionally cause #VE (such as WBINVD,
> +     * MONITOR, MWAIT) do not have corresponding TDCALL
> +     * [TDG.VP.VMCALL <Instruction>] leaves, since the TD has been designed
> +     * with no deterministic way to confirm the result of those operations
> +     * performed by the host VMM.  In those cases, the goal is for the TD
> +     * #VE handler to increment the RIP appropriately based on the VE
> +     * information provided via TDCALL.
> +     */
> +    case EXIT_REASON_WBINVD:
> +        pr_warn_once("WBINVD #VE Exception\n");
> +    case EXIT_REASON_MONITOR_INSTRUCTION:
> +        /* Handle as nops. */
> +        break;
> +    case EXIT_REASON_MWAIT_INSTRUCTION:
> +        /* MWAIT is supressed, not supposed to reach here. */
> +        pr_warn("MWAIT unexpected #VE Exception\n");
> +        return -EFAULT;
>    default:
>        pr_warn("Unexpected #VE: %d\n", ve->exit_reason);
>        return -EFAULT;
> -- 
> 2.25.1
>