On Mon, Dec 13, 2021 at 11:20:22PM +1100, Daniel Axtens wrote:
> Daniel Kiper <dki...@net-space.pl> writes:
>
> > On Thu, Nov 25, 2021 at 02:22:49AM +1100, Daniel Axtens wrote:
> >> grub_mm_init_region does some things that seem magical, especially
> >> around region merging. Make it a bit clearer.
> >>
> >> Signed-off-by: Daniel Axtens <d...@axtens.net>
> >> ---
> >> grub-core/kern/mm.c | 30 +++++++++++++++++++++++++++++-
> >> 1 file changed, 29 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/grub-core/kern/mm.c b/grub-core/kern/mm.c
> >> index bec960c18e2b..ef2025f929de 100644
> >> --- a/grub-core/kern/mm.c
> >> +++ b/grub-core/kern/mm.c
> >> @@ -128,23 +128,51 @@ grub_mm_init_region (void *addr, grub_size_t size)
> >> if (((grub_addr_t) addr + 0x1000) > ~(grub_addr_t) size)
> >> size = ((grub_addr_t) -0x1000) - (grub_addr_t) addr;
> >>
> >> + /* Attempt to merge this region with every existing region */
> >> for (p = &grub_mm_base, q = *p; q; p = &(q->next), q = *p)
> >> + /*
> >> + * Is the new region immediately below an existing region? That
> >> + * is, is the address of the memory we're adding now (addr) + size
> >> + * of the memory we're adding (size) + the bytes we couldn't use
> >> + * at the start of the region we're considering (q->pre_size)
> >> + * equal to the address of q? In other words, does the memory
> >> + * looks like this?
> >> + *
> >> + * addr q
> >> + * |----size-----|-q->pre_size-|<q region>|
> >> + */
> >> if ((grub_uint8_t *) addr + size + q->pre_size == (grub_uint8_t *) q)
> >> {
> >> + /*
> >> + * Yes, we can merge. r is our new region, it's address is the
> >> + * first GRUB_MM_ALIGNed address above addr.
>
> >
> > I think s/above/below/...
> >
> >> + */
> >> r = (grub_mm_region_t) ALIGN_UP ((grub_addr_t) addr, GRUB_MM_ALIGN);
>
> We do r = ALIGN_UP(addr, GRUB_MM_ALIGN), so 'above' is actually correct.
>
> But that probably indicates that I'm not explaining it well.
>
> How does this sound:
>
> /*
> * Yes, we can merge the memory starting at addr into the
> * existing region from below. Align up addr to GRUB_MM_ALIGN
> * so that our new region has proper alignment.
> */
>
> If you want you can change the comment and apply it, otherwise I will
> submit a v2.
Now it is better. I will update the patch and apply it together with the
other patches which got my RB.
Thanks,
Daniel
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