linux-kernel - Re: [PATCH v2] x86/boot: Use efi_setup_data for searching RSDP on kexec-ed kernel

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Date:   Wed, 3 Apr 2019 15:21:41 +0800
From:   Chao Fan <fanc.fnst@...fujitsu.com>
To:     Dave Young <dyoung@...hat.com>
CC:     Junichi Nomura <j-nomura@...jp.nec.com>,
        Borislav Petkov <bp@...en8.de>,
        "bhe@...hat.com" <bhe@...hat.com>,
        "kasong@...hat.com" <kasong@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] x86/boot: Use efi_setup_data for searching RSDP on
 kexec-ed kernel

On Wed, Apr 03, 2019 at 01:53:40PM +0800, Dave Young wrote:
>On 04/03/19 at 01:35pm, Chao Fan wrote:
>> On Tue, Apr 02, 2019 at 08:03:19PM +0800, Dave Young wrote:
>> >On 04/01/19 at 12:08am, Junichi Nomura wrote:
>> >> Commit 3a63f70bf4c3a ("x86/boot: Early parse RSDP and save it in
>> >> boot_params") broke kexec boot on EFI systems.  efi_get_rsdp_addr()
>> >> in the early parsing code tries to search RSDP from EFI table but
>> >> that will crash because the table address is virtual when the kernel
>> >> was booted by kexec.
>> >> 
>> >> In the case of kexec, physical address of EFI tables is provided
>> >> via efi_setup_data in boot_params, which is set up by kexec(1).
>> >> 
>> >> Factor out the table parsing code and use different pointers depending
>> >> on whether the kernel is booted by kexec or not.
>> >> 
>> >> Fixes: 3a63f70bf4c3a ("x86/boot: Early parse RSDP and save it in boot_params")
>> >> Signed-off-by: Jun'ichi Nomura <j-nomura@...jp.nec.com>
>> >> Acked-by: Baoquan He <bhe@...hat.com>
>> >> Cc: Chao Fan <fanc.fnst@...fujitsu.com>
>> >> Cc: Borislav Petkov <bp@...e.de>
>> >> Cc: Dave Young <dyoung@...hat.com>
>> [...]
>> >
>> >I failed to kexec reboot on my laptop, kernel panics too quick,  I'm not sure this is
>> >caused by your patch though.
>> >
>> >Actually there are something probably i915 changes break kexec,  the
>> >above test is with "nomodeset" which should work.
>> >
>> >Let me do more testing and update here tomorrow.
>> >
>> 
>> Hi Dave,
>> 
>> Last day I was testing the normal kexec, today I have tested the kdump
>> issue. Since the kdump has set "nokaslr" to cmdline, so I drop from
>> KDUMP_COMMANDLINE_APPEND
>> And it booted OK, so the PATCH works in both normal kexec and kdump.
>> 
>
>Actually I got some different kexec test results.
>
>Yesterday, with my installed kernel (based on git head several weeks
>ago), kexec kernel panics.
>
>Then I tried latest mainline with git pull, everything works, (with or
>without the patch, and can not reproduce the bug this patch is fixing)
>
>Today, test again, kexec reboot hangs (with or without your patch), but
>kdump works always (with or without the patch)

That's so strange, I'm puzzled by your test.
Withour ant changes, just test again, the result of yesterday and today
are different?

>
>It is weird to me. Probably I need find out why I can not reproduce the
>bug this patch is addressing first.

Hmm, is your laptop booted from EFI or legacy BIOS?
>
>earlyprintk seems not working for me anymore, it is not easy to debug on
>laptop now.

Another computer can help print the console message.
I remeber you are good at debug on two computers.

Thanks,
Chao Fan

>
>But the patch itself is clear, I think it should be good.  There might be
>other things broken.
>
>Thanks
>Dave
>
>