Re: [PATCH] do not keep interrupt window closed by sti in real mode

H. Peter Anvin
2009-04-08T16:13:46Z

Glauber Costa wrote:
>
> I get the idea from the pseudocode in sti description.
> It says:
> IF PE = 0 (* Executing in real-address mode *)
> THEN
> IF <- 1; (* Set Interrupt Flag *)
> ELSE (* Executing in protected mode or virtual-8086 mode *)
>
> There is no mention to any other activity besides setting the if flag.

But the same is true for the protected mode side of the instruction
description!

> Also, sti is used extensively in many places like the linux kernel for the
> guest, and it works just fine in kvm. So I was led to believe that real mode
> in fact behaving differently.

The difference is that at least under current Intel VT, VT only handles
protected mode -- the real mode runs purely in the interpreter.

> I'll take a look at avi's suggestion.

-hpa