Query about "Speculative Execution" Bug and RHEL Hosted In Virtualized Environments
If the virtualization layer (say, AWS, Azure, etc.) has been remediated and the CSP is eating the 30% hit at the hardware level, are guests riding that CSP hardware going to take a further 30% hit against their CPU allocation? Or, does the remediation set some kind of flag that gets passed up from the virtualization layer so that the fix-code sees "already safe - nothing for me to do at this layer"?
Responses
For the meltdown issue (primarily intel CPU's), the performance hit is from flushing the TLB (translation lookaside buffer) on every userspace/kernel transition. Userspace code spends a lot more time walking page tables to convert VM addresses into physical addresses as a result. You only take that hit once. Most workloads won't see 30% slowdown, but almost all workloads will see some slowdown. In the absence of a benchmark, assume something around 10%. Redhat has a more detailed analysis at https://access.redhat.com/articles/3307751.
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