[merged mm-nonmm-stable] efi-support-booting-with-kexec-handover-kho.patch removed from -mm tree

[merged mm-nonmm-stable] efi-support-booting-with-kexec-handover-kho.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: efi: support booting with kexec handover (KHO)
has been removed from the -mm tree.  Its filename was
     efi-support-booting-with-kexec-handover-kho.patch

This patch was dropped because it was merged into the mm-nonmm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Evangelos Petrongonas <epetron@amazon.de>
Subject: efi: support booting with kexec handover (KHO)
Date: Thu, 21 Aug 2025 17:59:00 +0000

When KHO (Kexec HandOver) is enabled, it sets up scratch memory regions
early during device tree scanning.  After kexec, the new kernel
exclusively uses this region for memory allocations during boot up to the
initialization of the page allocator

However, when booting with EFI, EFI's reserve_regions() uses
memblock_remove(0, PHYS_ADDR_MAX) to clear all memory regions before
rebuilding them from EFI data.  This destroys KHO scratch regions and
their flags, thus causing a kernel panic, as there are no scratch memory
regions.

Instead of wholesale removal, iterate through memory regions and only
remove non-KHO ones.  This preserves KHO scratch regions, which are good
known memory, while still allowing EFI to rebuild its memory map.

Link: https://lkml.kernel.org/r/b34da9fd50c89644cd4204136cfa6f5533445c56.1755721529.git.epetron@amazon.de
Signed-off-by: Evangelos Petrongonas <epetron@amazon.de>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Changyuan Lyu <changyuanl@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/firmware/efi/efi-init.c |   29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

--- a/drivers/firmware/efi/efi-init.c~efi-support-booting-with-kexec-handover-kho
+++ a/drivers/firmware/efi/efi-init.c
@@ -12,6 +12,7 @@
 #include <linux/efi.h>
 #include <linux/fwnode.h>
 #include <linux/init.h>
+#include <linux/kexec_handover.h>
 #include <linux/memblock.h>
 #include <linux/mm_types.h>
 #include <linux/of.h>
@@ -164,12 +165,32 @@ static __init void reserve_regions(void)
 		pr_info("Processing EFI memory map:\n");
 
 	/*
-	 * Discard memblocks discovered so far: if there are any at this
-	 * point, they originate from memory nodes in the DT, and UEFI
-	 * uses its own memory map instead.
+	 * Discard memblocks discovered so far except for KHO scratch
+	 * regions. Most memblocks at this point originate from memory nodes
+	 * in the DT and UEFI uses its own memory map instead. However, if
+	 * KHO is enabled, scratch regions, which are good known memory
+	 * must be preserved.
 	 */
 	memblock_dump_all();
-	memblock_remove(0, PHYS_ADDR_MAX);
+
+	if (is_kho_boot()) {
+		struct memblock_region *r;
+
+		/* Remove all non-KHO regions */
+		for_each_mem_region(r) {
+			if (!memblock_is_kho_scratch(r)) {
+				memblock_remove(r->base, r->size);
+				r--;
+			}
+		}
+	} else {
+		/*
+		 * KHO is disabled. Discard memblocks discovered so far:
+		 * if there are any at this point, they originate from memory
+		 * nodes in the DT, and UEFI uses its own memory map instead.
+		 */
+		memblock_remove(0, PHYS_ADDR_MAX);
+	}
 
 	for_each_efi_memory_desc(md) {
 		paddr = md->phys_addr;
_

Patches currently in -mm which might be from epetron@amazon.de are

Re: [merged mm-nonmm-stable] efi-support-booting-with-kexec-handover-kho.patch removed from -mm tree

[Ard Biesheuvel]

On Sun, 14 Sept 2025 at 02:36, Andrew Morton <akpm@linux-foundation.org> wrote:
>
>
> The quilt patch titled
>      Subject: efi: support booting with kexec handover (KHO)
> has been removed from the -mm tree.  Its filename was
>      efi-support-booting-with-kexec-handover-kho.patch
>
> This patch was dropped because it was merged into the mm-nonmm-stable branch
> of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
>
> ------------------------------------------------------
> From: Evangelos Petrongonas <epetron@amazon.de>
> Subject: efi: support booting with kexec handover (KHO)
> Date: Thu, 21 Aug 2025 17:59:00 +0000
>
> When KHO (Kexec HandOver) is enabled, it sets up scratch memory regions
> early during device tree scanning.  After kexec, the new kernel
> exclusively uses this region for memory allocations during boot up to the
> initialization of the page allocator
>
> However, when booting with EFI, EFI's reserve_regions() uses
> memblock_remove(0, PHYS_ADDR_MAX) to clear all memory regions before
> rebuilding them from EFI data.  This destroys KHO scratch regions and
> their flags, thus causing a kernel panic, as there are no scratch memory
> regions.
>
> Instead of wholesale removal, iterate through memory regions and only
> remove non-KHO ones.  This preserves KHO scratch regions, which are good
> known memory, while still allowing EFI to rebuild its memory map.
>
> Link: https://lkml.kernel.org/r/b34da9fd50c89644cd4204136cfa6f5533445c56.1755721529.git.epetron@amazon.de
> Signed-off-by: Evangelos Petrongonas <epetron@amazon.de>
> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> Acked-by: Pratyush Yadav <pratyush@kernel.org>
> Cc: Alexander Graf <graf@amazon.com>
> Cc: Ard Biesheuvel <ardb@kernel.org>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Changyuan Lyu <changyuanl@google.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

You forgot to apply my Reviewed-by - it's on the Link: thread.