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From:   Daniel Drake <drake@endlessm.com>
Date:   Tue, 27 Aug 2019 14:23:39 +0800
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Subject: Re: Early EFI-related boot freeze in parse_setup_data()
To:     linux-efi@vger.kernel.org,
        Linux Kernel <linux-kernel@vger.kernel.org>, x86@kernel.org
Cc:     Linux Upstreaming Team <linux@endlessm.com>
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On Fri, Aug 16, 2019 at 2:14 PM Daniel Drake <drake@endlessm.com> wrote:
> Anyway, the system freeze occurs in parse_setup_data(), specifically:
>
>         data = early_memremap(pa_data, sizeof(*data));
>         data_len = data->len + sizeof(struct setup_data);
>
> Dereferencing data->len causes the system to hang. I presume it
> triggers an exception handler due to some kind of invalid memory
> access.
>
> By returning early in that function, boot continues basically fine. So
> I could then log the details: pa_data has value 0x892bb018 and
> early_memremap returns address 0xffffffffff200018. Accessing just a
> single byte at that address causes the system hang.

I noticed a complaint about NX in the logs, right where it does the
early_memremap of this data (which is now at address 0x893c0018):

 Notice: NX (Execute Disable) protection missing in CPU!
 e820: update [mem 0x893c0018-0x893cec57] usable ==> usable
 e820: update [mem 0x893c0018-0x893cec57] usable ==> usable
 e820: update [mem 0x893b3018-0x893bf057] usable ==> usable
 e820: update [mem 0x893b3018-0x893bf057] usable ==> usable

Indeed, in the BIOS setup menu, "NX Mode" was Disabled.
Setting it to Enabled avoids the hang and Linux boots as normal. Weird!

Daniel