linux-kernel - Re: v4.4-rc8 based tip tree kernel hangs on boot.

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Date:	Mon, 18 Jan 2016 15:40:01 +0000
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>, linux-efi@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: v4.4-rc8 based tip tree kernel hangs on boot.

On Sun, 17 Jan, at 11:02:48PM, Srikar Dronamraju wrote:
> 
> Unfortunately even with your below patch on top of c9f2a9a ("x86/efi:
> Hoist page table switching code into efi_call_virt()" also fails to boot
> with and without CONFIG_DEBUG_WX=y. I have added CONFIG_EFI_PGT_DUMP.

What about if you comment out the call to efi_dump_pagetable()? What
if you return early from efi_sync_low_kernel_mappings(), e.g.

diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 71121a9d06cf..e1f8ebb88f84 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -177,6 +177,8 @@ void efi_sync_low_kernel_mappings(void)
 		init_mm.pgd + pgd_index(PAGE_OFFSET),
 		sizeof(pgd_t) * num_pgds);
 
+	return;
+
 	/*
 	 * We can share all PGD entries apart from the one entry that
 	 * covers the EFI runtime mapping space.

Do either of those modifications make your kernel boot when you apply
the patch I sent on Friday? If so, which one? I'm struggling to find
hardware that's similar enough to reproduce this.