Some processors may incur a machine check error possibly resulting in an unrecoverable CPU lockup when an instruction fetch encounters a TLB multi-hit in the instruction TLB. This can occur when the page size is changed along with either the physical address or cache type. The relevant erratum can be found here: https://bugzilla.kernel.org/show_bug.cgi?id=205195 There are other processors affected for which the erratum does not fully disclose the impact. This issue affects both bare-metal x86 page tables and EPT. It can be mitigated by either eliminating the use of large pages or by using careful TLB invalidations when changing the page size in the page tables. Just like Spectre, Meltdown, L1TF and MDS, a new bit has been allocated in MSR_IA32_ARCH_CAPABILITIES (PSCHANGE_MC_NO) and will be set on CPUs which are mitigated against this issue.
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| @@ -62,6 +62,8 @@ extern ssize_t cpu_show_mds(struct device *dev, · 61 unmodified lines | |||
| 62 | extern ssize_t cpu_show_tsx_async_abort(struct device *dev, | 62 | extern ssize_t cpu_show_tsx_async_abort(struct device *dev, |
| 63 | struct device_attribute *attr, | 63 | struct device_attribute *attr, |
| 64 | char *buf); | 64 | char *buf); |
| 65 | extern ssize_t cpu_show_itlb_multihit(struct device *dev, | ||
| 66 | struct device_attribute *attr, char *buf); | ||
| 65 | 67 | ||
| 66 | extern __printf(4, 5) | 68 | extern __printf(4, 5) |
| 67 | struct device *cpu_device_create(struct device *parent, void *drvdata, | 69 | struct device *cpu_device_create(struct device *parent, void *drvdata, |