Received-SPF: pass (google.com: domain of linux-kernel+bounces-89925-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Date: Sun, 3 Mar 2024 23:10:19 +0100
From: Borislav Petkov <bp@alien8.de>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Ard Biesheuvel <ardb+git@google.com>, linux-kernel@vger.kernel.org,
	Kevin Loughlin <kevinloughlin@google.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Dionna Glaze <dionnaglaze@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>, Brian Gerst <brgerst@gmail.com>
Subject: Re: [PATCH v7 2/9] x86/startup_64: Defer assignment of 5-level
 paging global variables
Message-ID: <20240303221019.GBZeT1S4295Y3MVuBG@fat_crate.local>
References: <20240227151907.387873-11-ardb+git@google.com>
 <20240227151907.387873-13-ardb+git@google.com>
 <20240228205540.GIZd-dzFYIBbtfIAo3@fat_crate.local>
 <CAMj1kXGhZU+FE2gE262Q8_vZEFHicsRtVPzXT-dhhCvBuiMjUA@mail.gmail.com>
 <20240301160921.GBZeH9sZhp73xX40ze@fat_crate.local>
 <CAMj1kXFJwEUExy7+Snh3QHVn-ATj0C+sYje22Qmc+y=cCtAV7g@mail.gmail.com>
 <20240301173323.GDZeIRY_BVBqpudkEo@fat_crate.local>
 <20240303192654.GAZeTO_nxJ4bE2A2zD@fat_crate.local>
 <CAMj1kXEmNWNH8ZRXcMQ=NKyvOWd4=K5kC4mZMzH-8BmBtvmw+A@mail.gmail.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <CAMj1kXEmNWNH8ZRXcMQ=NKyvOWd4=K5kC4mZMzH-8BmBtvmw+A@mail.gmail.com>

On Sun, Mar 03, 2024 at 10:56:49PM +0100, Ard Biesheuvel wrote:
> How are you passing the root device to the kernel? Via root= on the
> command line?

Yeah:

qemu
..
-kernel arch/x86/boot/bzImage
-append "root=/dev/sda2 resume=/dev/sda3 ...

> and this is OVMF.

Yap.

> I have tried both of these, with i440fx as well as q35, and they all
> work happily with my Debian guest image passed via -hda to QEMU, and
> with root=/dev/sda2 on the kernel command line.

Interesting. I'm not passing any machine type. Maybe I should even
thought I've never done it before.

/me goes and tries machine type.

Well, I'll be damned!

-machine type=pc-i440fx-2.8 - no workie BUT

-machine type=pc-q35-2.8

booted.

Now on to figure out what's different with q35 and why it is magical and
it finds the root device just fine:

[    2.732908] mount_root_generic: i: 2, fs_name: ext4
[    2.734275] do_mount_root: name: /dev/root
[    2.735093] kern_path: filename: ffff88800d4de000 of name: /root
[    2.736954] kern_path: ret: 0
[    2.737727] init_mount: kern_path(/root), ret: 0
[    2.738964] path_mount: will do_new_mount
[    2.739784] do_new_mount: 1, fc source: (null)
[    2.740961] do_new_mount: 2, err: 0
[    2.741722] do_new_mount: 3, err: 0
[    2.742448] do_new_mount: 4, err: 0
[    2.743164] vfs_get_tree: fc->root: 0000000000000000
[    2.744095] kern_path: filename: ffff88800d4de000 of name: /dev/root
[    2.745352] kern_path: ret: 0
[    2.745994] lookup_bdev: kern_path(/dev/root, , path: ffff88800cf163c0), error: 0
[    2.747288] lookup_bdev: inode->i_rdev: 0x800002
[    2.748163] get_tree_bdev: lookup_bdev(/dev/root, dev: 0x800002), error: 0
							  ^^^^^^^^^

> How did you get this output? Are these debug printk()s you added yourself?

Yeah, the good old "sprinkle printks" debugging method. Figured I should
look at the VFS code out of interest. :-)

Thanks a lot for the suggestions, especially about q35!

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette