缓存行是否刷新访问TLB？

Question

Assuming that we have intentionally thrashed the DTLB, and would like to proceed to flush a specific cache line from L1-3 using clflush on a memory region which is (most likely) disjoint from the addresses pointed to by the TLB entries; would this in fact bring the page base address of the cache line we are flushing back into the TLB?

In short, does a clflush touch the TLB at all? I'm assuming that due to this instruction honouring coherency, it will subsequently write that line back to memory (obviously needing a TLB look-up.)

Answer 1

From Intel® 64 and IA-32 Architectures Software Developer's Manual, Volume 2A: Instruction Set Reference, AL: "Invalidates the cache line that contains the linear address specified with the source operand from all levels of the processor cache hierarchy (data and instruction) ."

Since it uses the linear (virtual) address, the address needs to be translated, which means that a page table walk would be needed on a TLB miss. (This would generally be the case even for a different kind of instruction that pushed cache entries out to higher levels of cache since L1 caches are typically physically tagged for x86. In general, tagging with the virtual address has fallen out of favor. Using the physical address for tags means that the physical address is needed to check the cache for a hit, so even if it was not sent to memory, translation would be needed.)

While it would be possible to avoid loading the TLB for such accesses, the extra complexity of such special-case handling would almost certainly not be viewed as worth the bother given that CLFLUSH is not commonly used.