What's the expected behavior for LAM (linear address mask) is segmentation is enabled in 64bit mode?

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What's the expected behavior for LAM (linear address mask) is segmentation is enabled in 64bit mode?

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Sorry to bother you guys, but i just cannot think this through: since FS/GS could have a none-zero base, if a 64-bit pointer LinAddr = FS: EffAddr, how do we expect the masking behavior? in certain case, LinAddr[63] could be affected by arithmetic operation of the metadata, which seems weird to me. masking off the metadata before calculation is also improbable，since we cannot know the masking bits before figuring out LinAddr[63] first. Does that means that when LAM enabled, or the segment base address must be zero? (in that case this feature should be just called as effective address masking) other segment(-related) base address like IDTR/LDTR/GDTR may also suffer the same issue.

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