Re: [Xen-devel] [GRUB2 PATCH v4 3/4 - FOR REVIEW ONLY] multiboot2: Do not pass memory maps to image if EFI boot services are enabled

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Mar 15, 2016 at 04:26:00PM +0100, Daniel Kiper wrote:
> Do not pass memory maps to image if it asked for EFI boot services.

.. I would change this sentence a bit.

If image requested EFI boot services then skip multiboot2 memory maps.

> Main reason for not providing maps is because they will likely be
> invalid. We do a few allocations after filling them, e.g. for relocator
> needs. Usually we do not care as we would already finish boot services.

s/would already finish/would have finished/ ?

> If we keep boot services then it is easier to not provide maps. However,

s/easier/safer?/

> if image needs memory maps and they are not provided by bootloader then
> it should get them itself just before ExitBootServices() call.

s/them// ?

That is making an assumption that the user of Multiboot2 + EFI will
do this. Which is OK since only Xen is using it.. but is this
inline with the spec? Can you ignore not providing this information?


That aside - why not sync the multiboot memory map with what
the EFI one will be? Or is it too to complex to move the memory map
creation to a later phase of the bootup?

Wish there was some multboot memory map flag indicating 'STALE-CHECK-EFI'..


> 
> Signed-off-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
> v3 - suggestions/fixes:
>    - improve commit message
>      (suggested by Konrad Rzeszutek Wilk and Vladimir 'phcoder' Serbinenko).
> ---
>  grub-core/loader/multiboot_mbi2.c |   17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/grub-core/loader/multiboot_mbi2.c 
> b/grub-core/loader/multiboot_mbi2.c
> index 6c04402..ad1553b 100644
> --- a/grub-core/loader/multiboot_mbi2.c
> +++ b/grub-core/loader/multiboot_mbi2.c
> @@ -390,7 +390,7 @@ static grub_size_t
>  grub_multiboot_get_mbi_size (void)
>  {
>  #ifdef GRUB_MACHINE_EFI
> -  if (!efi_mmap_size)
> +  if (!keep_bs && !efi_mmap_size)
>      find_efi_mmap_size ();    
>  #endif
>    return 2 * sizeof (grub_uint32_t) + sizeof (struct multiboot_tag)
> @@ -755,6 +755,7 @@ grub_multiboot_make_mbi (grub_uint32_t *target)
>        }
>    }
>  
> +  if (!keep_bs)
>      {
>        struct multiboot_tag_mmap *tag = (struct multiboot_tag_mmap *) ptrorig;
>        grub_fill_multiboot_mmap (tag);
> @@ -776,6 +777,7 @@ grub_multiboot_make_mbi (grub_uint32_t *target)
>        / sizeof (grub_properly_aligned_t);
>    }
>  
> +  if (!keep_bs)
>      {
>        struct multiboot_tag_basic_meminfo *tag
>       = (struct multiboot_tag_basic_meminfo *) ptrorig;
> @@ -886,21 +888,17 @@ grub_multiboot_make_mbi (grub_uint32_t *target)
>      grub_efi_uintn_t efi_desc_size;
>      grub_efi_uint32_t efi_desc_version;
>  
> +    if (!keep_bs)
> +      {
>       tag->type = MULTIBOOT_TAG_TYPE_EFI_MMAP;
>       tag->size = sizeof (*tag) + efi_mmap_size;
>  
> -    if (!keep_bs)
>       err = grub_efi_finish_boot_services (&efi_mmap_size, tag->efi_mmap, 
> NULL,
>                                            &efi_desc_size, &efi_desc_version);
> -    else
> -      {
> -     if (grub_efi_get_memory_map (&efi_mmap_size, (void *) tag->efi_mmap,
> -                                  NULL,
> -                                  &efi_desc_size, &efi_desc_version) <= 0)
> -       err = grub_error (GRUB_ERR_IO, "couldn't retrieve memory map");
> -      }
> +
>       if (err)
>         return err;
> +
>       tag->descr_size = efi_desc_size;
>       tag->descr_vers = efi_desc_version;
>       tag->size = sizeof (*tag) + efi_mmap_size;
> @@ -908,6 +906,7 @@ grub_multiboot_make_mbi (grub_uint32_t *target)
>       ptrorig += ALIGN_UP (tag->size, MULTIBOOT_TAG_ALIGN)
>         / sizeof (grub_properly_aligned_t);
>        }
> +  }
>  
>    if (keep_bs)
>      {
> -- 
> 1.7.10.4
> 

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