Subject: Re: Kernel 4.7: PAGE_GUARDED and _PAGE_NO_CACHE

From: Michael Ellerman <[email-masked]>
Date: Mon, 06 Jun 2016 10:57:59 +1000

On Sun, 2016-06-05 at 18:09 +0200, Christian Zigotzky wrote:

> All,
> 
> I need an answer because I think Darren's guess is correct. It isn't a 
> problem in the pci code. I replaced the file head_64.S that Darren 
> mentioned with the one from the kernel 4.6 and it compiled but 
> unfortunately it doesn't boot. We know "head_64.S" is one file for the 
> early boot phase but I think there are some other files.

There's lots of files used in the early boot, you can't revert individual files
and expect it to work.

> On 28 May 2016 at 8:51 PM, Darren Stevens wrote:
> > You can see from this that the 4.7 kernel hangs right after the booting linux
> > via __start(), whereas in the 4.4 there's about 29 lines of output before it
> > gets to the Initialised io_base_virt printk in our patch.

If the last thing you see is "booting linux via __start()" that means the kernel
crashed early, before it could detect and initialise the console.

Do you have a serial or other console in that machine at a known location? If so
you can hard-code the kernel to use that console, which means you can get
messages earlier in boot. See udbg_early_init() for starters.

cheers