Re: [PATCH v2] vmx: Handle TDX instruction exit reasons

[Teddy Astie <teddy.astie@xxxxxxxxxx>]

Le 21/09/2026 à 13:07, Jan Beulich a écrit :
> On 10.09.2026 16:17, Teddy Astie wrote:
> > On hardware that supports TDX, guests can cause VMEXIT related to
> > TDX instructions (SEAMCALL and TDCALL) regardless of VMCS configuration.
> Can they? SEAMCALL pseudocode has
>
> ELSIF IA32_SEAMRR_MASK.VALID = 0 or events blocked by MOV SS
> THEN #GP(0);
> ELSIF SEAM is globally disabled
> THEN VMFailInvalid;
Earlier in the if chain, there is

ELSIF in VMX non-root operation
THEN VM exit;

When running inside the guest, we're effectively in VMX non-root mode, 
which would trigger the VMEXIT.
This issue is documented in a dedicated Intel advisory [1] (there is 
also microcode bug CVE-2024-22374 which makes it triggerable from guest 
userland).
[1] 
https://www.intel.com/content/dam/www/public/us/en/security-advisory/documents/intel_tdx_joint_security_review_with_microsoft.pdf 
(Vulnerability 6)
> For TDCALL I see
>
> IF not in SEAM non-root operation and not in VMX non-root operation
> THEN #UD;
>
> which may indeed not be sufficient, but the SEAMCALL conditions shouldn't
> be met under present Xen?
TDCALL probably don't need it, but I don't think this is wrong to treat 
it similarly (like KVM does [2]).
> Jan
[2] https://lore.kernel.org/all/20251016182148.69085-2-seanjc@xxxxxxxxxx/

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