Re: [RFC PATCH 1/4] efi/libstub: Decouple memory bitmap from the unaccepted table

[Kiryl Shutsemau <kas@kernel.org>]

On Wed, Nov 26, 2025 at 04:27:19PM -0600, Pratik R. Sampat wrote:
> Hi Kiryl,
> 
> Thanks for you comments.
> 
> On 11/26/25 5:08 AM, Kiryl Shutsemau wrote:
> > On Tue, Nov 25, 2025 at 11:57:50AM -0600, Pratik R. Sampat wrote:
> >> Memory hotplug in secure environments requires the unaccepted memory
> >> bitmap to grow as new memory is added. Currently, the bitmap is
> >> implemented as a flexible array member at the end of struct
> >> efi_unaccepted_memory, which is reserved by memblock at boot and cannot
> >> be resized without reallocating the entire structure.
> >>
> >> Replace the flexible array member with a pointer.
> > 
> > Well, it break interoperability between kernel before and after the
> > patch. Consider kexec from kernel without the patch to the kernel with
> > the patch and then back to older kernel. It is ABI break.
> > 
> > Is re-allocating the entire structure such a big pain?
> > 
> 
> We could do that. My concern is that we would then need to protect the
> entire table instead of just the bitmap, which may add an additional
> overhead?

What additional overhead? The main contention is going to be on binmap
anyway.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov