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Andrew Cooper
28301682f4
xc_cpuid_apply_policy() provides compatibility for migration of a pre-4.14 VM where no CPUID data was provided in the stream. It guesses the various max-leaf limits, based on what was true at the time of writing, but this was not correctly adapted when speculative security issues forced the advertisement of new feature bits. Of note are: * LFENCE-DISPATCH, in leaf 0x80000021.eax * BHI-CTRL, in leaf 0x7[2].edx In both cases, a VM booted on a security-patched Xen 4.13, and then migrated on to any newer version of Xen on the same or compatible hardware would have these features stripped back because Xen is still editing the cpu-policy for sanity behind the back of the toolstack. For VMs using BHI_DIS_S to mitigate Native-BHI, this resulted in a failure to restore the guests MSR_SPEC_CTRL setting: (XEN) HVM d7v0 load MSR 0x48 with value 0x401 failed (XEN) HVM7 restore: failed to load entry 20/0 rc -6 Fixes:e9b4fe2636("x86/cpuid: support LFENCE always serialising CPUID bit") Fixes:f3709b15fc("x86/cpuid: Infrastructure for cpuid word 7:2.edx") Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Reviewed-by: Jan Beulich <jbeulich@suse.com>