Re: Spectre on non-amd64

[maya%netbsd.org@localhost]

Spectre variant 2 also relies on me being able to poison the branch
target buffer. loongson had a similar issue where errant BTB entries
would cause hangs, and they then claimed this at kernel entry clears
out their BTB:*

		jal	1f
		 nop
1:		jal	1f
		 nop
1:		jal	1f
		 nop
1:		jal	1f
		 nop
1: 

A question is whether that works for other branch predictors, and
how many we would need.

* https://github.com/torvalds/linux/blob/2d6349944d967129c1da3c47287376f10121dbe1/arch/mips/include/asm/stackframe.h#L152-L164