linux-kernel - Re: [4.4] broken conversion from efi to kernel page table

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Date:   Fri, 12 Jan 2018 08:52:47 -0500
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Steve Sistare <steven.sistare@...cle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
        hpa@...or.com, x86@...nel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hugh Dickins <hughd@...gle.com>, dave.hansen@...ux.intel.com,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [4.4] broken conversion from efi to kernel page table

Hi Jiri,

This patch solves a different problem than _PAGE_NX. The problem it
solves is similar to
+      efi_pgd = (pgd_t *)__get_free_pages(gfp_mask,
PGD_ALLOCATION_ORDER);, Where after applying PTI mask CR3 can point to
invalid page table.
But, this patch is specific to stable 4.4.110 since it uses
trampoline_pgd from realmode, instead of allocating its own page table
as 4.6 and later do.

Thank you,
Pavel

On Fri, Jan 12, 2018 at 5:04 AM, Jiri Kosina <jikos@...nel.org> wrote:
> On Thu, 11 Jan 2018, Pavel Tatashin wrote:
>
>> This fixes boot panics, hangs which I reported in this thread:
>
> Are you using EFI old_memmap?
>
> If so, then
>
>         https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=x86/pti&id=de53c3786a3ce162a1c815d0c04c766c23ec9c0a
>
> ("x86/pti: Unbreak EFI old_memmap") should be the cure.
>
> If not, you might be missing this in in arch/x86/platform/efi/efi_64.c
>
> -      efi_pgd = (pgd_t *)__get_free_page(gfp_mask);
> +      efi_pgd = (pgd_t *)__get_free_pages(gfp_mask, PGD_ALLOCATION_ORDER);
>
> Could you please let me know if either of this fixes your problem?
>
> Thanks,
>
> --
> Jiri Kosina
> SUSE Labs
>