Re: [Xen-devel] [PATCH] x86: defer not-present segment checks

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.10.16 at 15:01, <JBeulich@xxxxxxxx> wrote:
> Also note how e.g. emulate_gate_op() looks at the P bit of the gate
> only after having done other relevant checks. Having looked at this
> again just now I realize, though, that the P bit clear on the code
> segment descriptor wrongly raises #GP. As this gets fixed by the
> rework patch using the generic insn decoder, I won't bother submitting
> a separate fix for this though; I'll just add a note to that patch's
> commit message.

Actually I was wrong here - it's the check of the descriptor of an
already loaded segment register that does this, so there's nothing
wrong with raising #GP when it ends up being no longer present
at that point (as there's no architectural exception in this case,
using #GP uniformly is likely better than trying to be creative).

Jan


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