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Re: [Xen-devel] [PATCH] x86/traps: Avoid the #GP slowpath for guest #DB exceptions

>>> On 08.01.15 at 14:25, <andrew.cooper3@xxxxxxxxxx> wrote:
> do_debug() is capable of correctly dealing with #DB exceptions in guest
> context, and indeed needs to be as the 'icebp' instruction skips the DPL
> check anyway.

I don't follow: ICEBP doesn't check DPL, right, but what does setting
DPL to 3 buy us? Other than for INTO and INT3, we don't want to
encourage use of INT $0x01 instructions, nor am I aware of anyone
commonly using them. Yet afaict only they would be affected by your
change. Actual #DB, just like any other hardware exceptions, don't
consider DPL just like ICEBP doesn't.


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