Re: [PATCH v2] x86/unaccepted_memory: Do not accept ranges that are no longer E820 RAM

[Kiryl Shutsemau <kas@kernel.org>]

On Fri, Nov 13, 2026 at 04:55:54AM -0600, Pankaj Gupta wrote:
> Accept only whole pages of E820 RAM, and clear the bitmap bits only for the
> units in which memory was accepted.

A bit in the bitmap covers the whole unit. If the hole doesn't start and
end on a unit boundary, the unit at its edge is only partly accepted, but
its bit gets cleared. The rest of the unit stays unaccepted and nothing
records it.

This kernel never touches the hole, but the next one can. memmap= and mem=
only edit e820_table. kexec_file_load() hands the next kernel
e820_table_kexec, which is copied before the command line is parsed and
still has the hole as RAM. The next kernel finds RAM with a clear bit and
uses it. memmap=1M$0x1fff00000, then kexec into a kernel without it.

On TDX this is new. tdx_accept_memory() works on physical addresses, so
today the hole is accepted together with the rest of the unit and the
bitmap stays correct. Only SNP needs the direct mapping.

A unit cannot be half accepted. Given that, should we go with what Ard
suggested and refuse memmap= holes in unaccepted memory instead?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov