Re: [PATCH 1/2] efi: Fix reservation of unaccepted memory table

[Mike Rapoport]

On Mon, Feb 16, 2026 at 07:53:24AM -0800, Dave Hansen wrote:
> On 2/14/26 07:51, Mike Rapoport wrote:
> > Heh, it's x86's choice of memblock iterator that's rounding the ranges 😉
> 
> Ahh, good point. I was just assuming that the memblock iteration _had_
> to be over PFNs. Silly me.
> 
> > Maybe I miss some context, but my understanding is that for crash kernels
> > the unaccepted table is E820_TYPE_RESERVED and those are never added to
> > memblock.memory by e820 code, hence the call to memblock_add() in
> > reserve_unaccepted().
> > 
> > When x86 creates page tables, init_range_memory_mapping() walks
> > memblock.memory with for_each_mem_pfn_range() that rounds ranges that are
> > not page-aligned, which is normally fine, because it would mean that we
> > miss some partial pages that are divided between E820_RAM and
> > E820_SOMETHING_ELSE.
> > 
> > And Kiryl's intention to round up unaccepted to page boundary seems correct
> > to me.
> 
> It fixes the bug for sure.
> 
> I'm more worried about the next feature, or the existing features that
> also only working because memory is page-aligned somewhere (even though
> it isn't guaranteed to remain that way).
> 
> There are two choices for fixing this: One, we do Kiryl's fix plus
> checks to ensure that all the memblocks that generate direct mappings
> (is it _just_ the "memory" type?) are padded out to page-aligned boundaries.
> 
> The other alternative is to do for_each_mem_range() and do the padding
> universally when creating the mappings. Maybe _also_ with warnings or
> maybe a pr_debug().
> 
> I do still think it's a little wonky for memblock_add()'s management of
> the "memory" type to allow unaligned arguments when that type is also
> used to create page-aligned mapping structures. Memblocks themselves
> obviously need to be byte-level, but I'm not sure it's the right thing
> for the "memory" type API.

Well, we could make memblock_add() implicitly cut down the edges when it's
adding to memblock.memory and make everything there page aligned, but I
truly have no idea what will break and I'm sure something will :)

Another thing that's more on x86 side, is that translation from e820 to
memblock only adds E820_TYPE_RAM to memblock. And since in e820 these are
mutually exclusive with other e820 types, this could create non-aligned
chunks when firmware reservations are not page aligned. It also creates
unnecessary holes in memblock.memory that slow down memblock interation a
bit and more interestingly, everything that's not in E820_TYPE_RAM is
treated as IO and requires ioremap/memremap for access, even it is in DRAM.

If these reserved regions were added to memblock.memory along with being
memblock_reserve()ed we wouldn't hit the bug with unaccepted I believe some
others as well.

-- 
Sincerely yours,
Mike.