linux-kernel - Re: [PATCH 0/3] Resolve problems with kexec identity mapping

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Message-ID: <20240708181133.GHZowr1eznPqgvdtRw@fat_crate.local>
Date: Mon, 8 Jul 2024 20:11:33 +0200
From: Borislav Petkov <bp@...en8.de>
To: Steve Wahl <steve.wahl@....com>
Cc: Ard Biesheuvel <ardb@...nel.org>, Ashish Kalra <ashish.kalra@....com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Pavin Joseph <me@...injoseph.com>,
	Eric Hagberg <ehagberg@...il.com>,
	Simon Horman <horms@...ge.net.au>,
	Eric Biederman <ebiederm@...ssion.com>,
	Dave Young <dyoung@...hat.com>, Sarah Brofeldt <srhb@....dk>,
	Russ Anderson <rja@....com>, Dimitri Sivanich <sivanich@....com>,
	Hou Wenlong <houwenlong.hwl@...group.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>, Yuntao Wang <ytcoode@...il.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Joerg Roedel <jroedel@...e.de>,
	Michael Roth <michael.roth@....com>
Subject: Re: [PATCH 0/3] Resolve problems with kexec identity mapping

On Mon, Jul 08, 2024 at 10:42:47AM -0500, Steve Wahl wrote:
> So I looked at the code more closely, and I don't think boot_page_fault is
> going to work prior to the call to initialize_identity_maps.  In the current
> flow in head_64.S, that comes after load_stage2_idt, where here we were
> trying to use it just after load_stage1_idt, quite a bit earlier.

But still after setting up the #PF handlers in both cases. So it can't be
that.

> Is there a reason you want to avoid having these areas already entered
> in the identity map setup by kexec?

Well, imagine my one-liner worked. Can you think of a reason then?

So, theoretically, this should be reproducible in a VM too, I'd say. If we
could manage to get that EFI config table placed at the right address, to be
outside of a 1G page so that it doesn't get covered by a Gb mapping.

Or use "nogbpages" and then maybe perhaps with Ard's help hack up OVMF to do
so. :)

So, can someone with such a box boot with "efi=debug" on the kernel cmdline so
that we can try to reproduce the memory layout in a VM?

Thx.

-- 
Regards/Gruss,
    Boris.

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