linux-kernel - Re: [PATCH] x86/boot/64: Initialize 5-level paging variables earlier

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Date:   Tue, 13 Oct 2020 10:59:05 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     x86@...nel.org, Borislav Petkov <bp@...en8.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/boot/64: Initialize 5-level paging variables earlier

Hi Arvind,

On Sat, Oct 10, 2020 at 03:11:10PM -0400, Arvind Sankar wrote:
> Commit
>   ca0e22d4f011 ("x86/boot/compressed/64: Always switch to own page table")
> started using a new set of pagetables even without KASLR.
> 
> After that commit, initialize_identity_maps() is called before the
> 5-level paging variables are setup in choose_random_location(), which
> will not work if 5-level paging is actually enabled.
> 
> Fix this by moving the initialization of __pgtable_l5_enabled,
> pgdir_shift and ptrs_per_p4d into cleanup_trampoline(), which is called
> immediately after the finalization of whether the kernel is executing
> with 4- or 5-level paging. This will be earlier than anything that might
> require those variables, and keeps the 4- vs 5-level paging code all in
> one place.
> 
> Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
> ---
>  arch/x86/boot/compressed/ident_map_64.c |  6 ------
>  arch/x86/boot/compressed/kaslr.c        |  8 --------
>  arch/x86/boot/compressed/pgtable_64.c   | 16 ++++++++++++++++
>  3 files changed, 16 insertions(+), 14 deletions(-)

Thanks for fixing this! It is not only a fix but also a nice cleanup of
the 5level-paging initialization code.

Reviewed-by: Joerg Roedel <jroedel@...e.de>
Tested-by: Joerg Roedel <jroedel@...e.de>