pgsql: instrumentation: Avoid CPUID 0x15/0x16 for Hypervisor TSC freque

instrumentation: Avoid CPUID 0x15/0x16 for Hypervisor TSC frequency

This restricts the retrieval of the TSC frequency whilst under a Hypervisor to
either Hypervisor-specific CPUID registers (0x40000010), or TSC
calibration. We previously allowed retrieving from the traditional CPUID
registers for TSC frequency (0x15/0x16) like on bare metal, but it turns out
that they are not trustworthy when virtualized and can report wildly incorrect
frequencies, like 7 kHz when the actual calibrated frequencty is 2.5 GHz.

Per report from buildfarm member drongo.

Author: Lukas Fittl <lukas(at)fittl(dot)com>
Reviewed-by: Andres Freund <andres(at)anarazel(dot)de>
Discussion: https://postgr.es/m/jr4hk2sxhqcfpb67ftz5g4vw33nm67cgf7go3wwmqsafu5aclq%405m67ukuhyszz

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7fc36c5db55016f7a1d89b5e2efd82fe6fd39632

Modified Files
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src/port/pg_cpu_x86.c | 21 +++++++++------------
1 file changed, 9 insertions(+), 12 deletions(-)