linux-kernel - Re: efi boot failures due to PTI with 32 bit builds and Intel CPUs

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Date:   Thu, 30 Aug 2018 09:19:51 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Michal Hocko <mhocko@...e.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        Dave Hansen <dave.hansen@...el.com>,
        Pavel Machek <pavel@....cz>
Subject: Re: efi boot failures due to PTI with 32 bit builds and Intel CPUs

Hey Guenter,

On Wed, Aug 29, 2018 at 01:16:59PM -0700, Guenter Roeck wrote:
> I see boot failures on mainline when trying to boot x86 images with an efi
> bios on Intel CPUs in qemu. Behavior is quite unusual: qemu dies silently
> after the kernel displays "Run /sbin/init as init process". With debugging
> enabled, qemu reports a CR3 update followed by a triple fault.
> Here is the end of the log file:
> 
> ----------------
> IN:
> 0xc75f1d1a:  66 90                    nop
> 0xc75f1d1c:  0f 20 d8                 movl     %cr3, %eax
> 0xc75f1d1f:  0d 00 10 00 00           orl      $0x1000, %eax
> 0xc75f1d24:  0f 22 d8                 movl     %eax, %cr3
> 
> CR3 update: CR3=0e39b000

Thanks for the bug report, from a quick glance it looks like the kernel
is switching to an empty page-table. But I need to debug that further.

> qemu-system-i386 -kernel arch/x86/boot/bzImage -M q35 -cpu core2duo \
> 	-no-reboot -m 256 \
> 	-bios OVMF-pure-efi-32.fd \
> 	-usb -device usb-storage,drive=d0 \
> 	-drive file=rootfs.ext2,if=none,id=d0,format=raw \
> 	--append 'root=/dev/sda rw rootwait mem=256M console=ttyS0 console=tty noreboot' \
> 	-nographic

Can you please provide the exact OVMF-pure-efi-32.fd image and the
.config of the kernel?

Thanks a lot,

       Joerg