linux-kernel - Re: [PATCH v2 5/5] efi/x86: Don't relocate the kernel unless necessary

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Date:   Tue, 3 Mar 2020 18:34:58 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        linux-efi <linux-efi@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/5] efi/x86: Don't relocate the kernel unless
 necessary

On Wed, Mar 04, 2020 at 12:08:33AM +0100, Ard Biesheuvel wrote:
> On Tue, 3 Mar 2020 at 23:12, Arvind Sankar <nivedita@...m.mit.edu> wrote:
> >
> > Add alignment slack to the PE image size, so that we can realign the
> > decompression buffer within the space allocated for the image.
> >
> > Only relocate the kernel if it has been loaded at an unsuitable address:
> > * Below LOAD_PHYSICAL_ADDR, or
> > * Above 64T for 64-bit and 512MiB for 32-bit
> >
> > For 32-bit, the upper limit is conservative, but the exact limit can be
> > difficult to calculate.
> >
> 
> Could we get rid of the call to efi_low_alloc_above() in
> efi_relocate_kernel(), and just allocate top down with the right
> alignment? I'd like to get rid of efi_low_alloc() et al if we can.
> 

But we don't have a top-down allocator, do we? ALLOCATE_MAX_ADDRESS
guarantees the maximum, but it doesn't guarantee that you'll be as high
as possible.