linux-kernel - Re: [tip: x86/urgent] x86/setup: Always reserve the first 1M of RAM

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Date:   Fri, 3 Mar 2023 11:10:22 +0200
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Borislav Petkov <bp@...e.de>, Hugh Dickins <hughd@...gle.com>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [tip: x86/urgent] x86/setup: Always reserve the first 1M of RAM

Hi Andy,

On Wed, Mar 01, 2023 at 07:51:43PM -0800, Andy Lutomirski wrote:
> On Thu, Jun 3, 2021, at 11:01 AM, tip-bot2 for Mike Rapoport wrote:
> >
> > x86/setup: Always reserve the first 1M of RAM
> >

...

> +       /*
> +        * Unconditionally reserve the entire fisrt 1M, see comment in
> +        * setup_arch().
> +        */
> +       memblock_reserve(0, SZ_1M);
> 
> 
> But this runs even if we just failed to allocate a trampoline on the
> first try, again dooming the kernel to panic.
> 
> I real the commit message and the linked bug, and I'm having trouble
> finding evidence of anything actually fixed by this patch.  Can we just
> revert it?  If not, it would be nice to get a fixup patch that genuinely
> cleans this up -- the whole structure of the code (first, try to allocate
> trampoline, then free boot services, then try again) isn't really
> conducive to a model where we *don't* free boot services < 1M.
 
Currently, the second attempt to set_real_mode_mem() in
efi_free_boot_services() does not allocate from memblock anyway but reuses
memory freed from EFI services. Could be that failure to boot caused by
another failing reservation?
 
> Discovered by my delightful laptop, which does not boot with this patch applied.

Do you have early_printk() visible? 
 
> --Andy

-- 
Sincerely yours,
Mike.