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


> On Mar 26, 2021, at 5:18 PM, Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> 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@linux.intel.com>
> Reviewed-by: Andi Kleen <ak@linux.intel.com>
> ---
>
> 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
>

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