When IA32_ARCH_CAPABILITIES (0x10a) can't be read from userspace (no msr
module, or kernel lockdown under Secure Boot), the FBSDP_NO/PSDP_NO/SBDR_SSDP_NO
bits were left at 0 ("explicitly not immune") instead of -1 ("unknown"). For a
recent CPU not in any kernel model list (e.g. Arrow Lake), this wrongly flipped
the MMIO Stale Data verdict into the "out of servicing period, Intel never
assessed this CPU" bucket.
(cherry picked from commit 23ea5427b5)
Inside a Xen PVH domU (and any guest where the kernel sets
X86_FEATURE_HYPERVISOR), the kernel appends "; SMT Host state unknown"
to the MDS/MMIO sysfs vuln string: the host controls SMT scheduling and
the guest genuinely can't see it. The "SMT is either mitigated or
disabled" check only matched 'SMT (disabled|mitigated)', so this read as
"not mitigated" and --paranoid flipped the verdict to a misleading
VULN "you must disable SMT (Hyper-Threading)".
Make *_smt_mitigated a tri-state: 1 (disabled/mitigated), 0 (vulnerable),
and 2 (host state unknown). In paranoid mode, when the in-guest
mitigation is active but SMT host state is unknown, report UNK with an
explanation that cross-thread protection depends on the hypervisor host's
SMT/core-scheduling config, instead of VULN. PV DomUs (kernel reports
"SMT vulnerable", no HYPERVISOR bit) are unchanged and still flagged.
(cherry picked from commit 1e33f40f0a)
Stéphane Lesimple