Re: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions

From: Linus Torvalds
Date: Sat May 04 2019 - 16:37:12 EST

On Sat, May 4, 2019 at 1:12 PM Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> As an aside, is it even *possible* to get #BP from v8086 mode? On a quick SDM read, the INT3 instruction causes #GP if VM=1 and IOPL<3. And, if we allow vm86() to have IOPL=3, we should just remove that ability. Itâs nuts.

Oh, and I think you mis-read the SDM.

Yes, iopl matters for "int X" (cd xx) instruction in vm86 mode.

But no, iopl does *not* matter for the special "int3/into/int1"
(cc/ce/f1) instructions, I think.