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

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H. Peter Anvin wrote:
Glauber Costa wrote:
While in real mode, sti does not block interrupts from the subsequent
instruction. This is stated at Intel SDM Volume 2b, page 4-432

I don't see how you're getting that idea from the STI documentation --
and I am quite sure that that is not the case.  Quite on the contrary.
The only differences between protected mode and real mode has to do with
the handling of VIF when CPL=3 (this rather naturally falls out if one
considers CPL=0 in real mode).

I'm guessing the problem is due to the second instruction. We don't clear the 'blocked by interrupt shadow' flag when we emulate, which extends interrupt shadow by one more instruction. If the instruction sequence is 'sti hlt' we end in an inconsistent state.



--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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