Re: [PATCH v3 6/6] efi: restrict arm/arm64 linux loader initrd placement

[Leif Lindholm]

On Fri, Jul 06, 2018 at 06:00:11PM +0200, Daniel Kiper wrote:
> On Wed, Jun 27, 2018 at 06:17:20PM +0100, Leif Lindholm wrote:
> > The 32-bit arm Linux kernel is built as a zImage, which self-decompresses
> > down to near start of RAM. In order for an initrd/initramfs to be
> > accessible, it needs to be placed within the first ~768MB of RAM.
> > The initrd loader built into the kernel EFI stub restricts this down to
> > 512MB for simplicity - so enable the same restriction in grub.
> >
> > For arm64, the requirement is within a 1GB aligned 32GB window also
> > covering the (runtime) kernel image. Since the EFI stub loader itself
> > will attempt to relocate to near start of RAM, force initrd to be loaded
> > completely within the first 32GB of RAM.
> >
> > Signed-off-by: Leif Lindholm <address@hidden>
> > ---
> >  grub-core/loader/arm64/linux.c | 39 ++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 38 insertions(+), 1 deletion(-)
> >
> > diff --git a/grub-core/loader/arm64/linux.c b/grub-core/loader/arm64/linux.c
> > index 577fbda54..0d550182f 100644
> > --- a/grub-core/loader/arm64/linux.c
> > +++ b/grub-core/loader/arm64/linux.c
> > @@ -193,6 +193,42 @@ grub_linux_unload (void)
> >    return GRUB_ERR_NONE;
> >  }
> >
> > +/*
> > + * This function returns a pointer to a legally allocated initrd buffer,
> > + * or NULL if unsuccessful
> > + */
> > +static void *
> > +allocate_initrd_mem (int initrd_pages)
> > +{
> > +  grub_addr_t max_addr;
> > +
> > +  if (grub_efi_get_ram_base (&max_addr) != GRUB_ERR_NONE)
> > +    return NULL;
> > +
> > +  /*
> > +   * As per linux/Documentation/arm/Booting
> > +   * ARM initrd needs to be covered by kernel linear mapping,
> > +   * so place it in the first 512MB of DRAM.
> > +   *
> > +   * As per linux/Documentation/arm64/booting.txt
> > +   * ARM64 initrd needs to be contained entirely within a 1GB aligned 
> > window
> > +   * of up to 32GB of size that covers the kernel image as well.
> > +   * Since the EFI stub loader will attempt to load the kernel near start 
> > of
> > +   * RAM, place the buffer in the first 32GB of RAM.
> > +   */
> > +#ifdef __arm__
> > +#define INITRD_MAX_ADDRESS_OFFSET (512U * 1024 * 1024)
> > +#else /* __aarch64__ */
> > +#define INITRD_MAX_ADDRESS_OFFSET (32ULL * 1024 * 1024 * 1024)
> > +#endif
> 
> May I ask you to move these definitions together with the comment before
> the allocate_initrd_mem(). Or even to the beginning of the file just
> behind GRUB_MOD_LICENSE(). I prefer the latter. Though I am not
> insisting on it.

I'm OK with either. I stuck it here because it is information that is
_only_ relevant to this particular piece of code. So my preference
leans the other way. Will update for v4.

/
    Leif