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Re: [PATCH 1/5] x86/pv: Fix the determiniation of whether to inject #DB
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 14 Sep 2023 17:13:49 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Jinoh Kang <jinoh.kang.kr@xxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 14 Sep 2023 15:13:56 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 14.09.2023 16:49, Andrew Cooper wrote:
> On 14/09/2023 3:40 pm, Jan Beulich wrote:
>> On 13.09.2023 01:21, Andrew Cooper wrote:
>>> We long ago fixed the emulator to not inject exceptions behind our back.
>>> Therefore, assert that that a PV event (including interrupts, because that
>>> would be buggy too) isn't pending, rather than skipping the #DB injection if
>>> one is.
>>>
>>> On the other hand, the io_emul() stubs which use X86EMUL_DONE rather than
>>> X86EMUL_OKAY may have pending breakpoints to inject after the IO access is
>>> complete, not to mention a pending singlestep.
>> If you look at the uses of X86EMUL_DONE you'll see that this error code is
>> not intended to ever come back from the emulator. It's solely used to
>> communicate between hooks and the core emulator. Therefore I think this
>> part of the description and the added case label are wrong here. With them
>> dropped again ...
>
> Oh. I see that now you've pointed it out, but it's far from clear.
>
> I'd suggest that we extend the the debug wrapper for x86_emulate() with
> an assertion to this effect. It also has a knock-on effect in later
> patches.
>
> With the DONE part dropped, this probably wants merging into patch 4.
> Thoughts?
Not sure. Even then the patch here looks to still make sense on its own.
I don't mind the folding, I guess, but for the moment the two R-b are
only on the individual patches.
Jan
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