[PATCH 0/7] LoongArch: add KHO support and selftests

[PATCH 0/7] LoongArch: add KHO support and selftests

[George Guo]

From: George Guo <guodongtai@kylinos.cn>>

This series adds Kexec Handover (KHO) support for LoongArch64 and
extends the KHO selftest infrastructure to run on LoongArch under QEMU.

KHO support (patches 1-2)
--------------------------
Patch 1 wires up the three pieces needed for KHO on LoongArch:
 - Kconfig: select ARCH_SUPPORTS_KEXEC_HANDOVER for 64BIT
 - machine_kexec_file: call cmdline_add_kho() to pass the KHO FDT and
   scratch buffer addresses via "kho_handover=" on the kernel cmdline
 - setup: parse "kho_handover=" early and call kho_populate()

Patch 2 fixes a duplicate-parameter bug when kexec is invoked with
--reuse-cmdline: the running kernel's cmdline already contains a stale
kho_handover= from the previous load.  load_other_segments() prepends a
fresh entry but appends the original cmdline verbatim, so early_param()
calls kho_populate() twice and the second call overwrites the first with
a stale FDT pointer, panicking early in mm_core_init().

Bug fixes (patches 3-4)
------------------------
Patch 3 fixes a build failure with CONFIG_KFENCE=y: virt_to_phys() and
phys_to_virt() in asm/io.h expand to use offset_in_page() and
page_address(), which require <linux/mm.h> that was not included.

Patch 4 moves KEXEC_CONTROL_CODE from 0x100000 to 0x180000.  QEMU
places its machine FDT at 0x100000 when booting with '-kernel'; the
previous placement silently overwrote the FDT with the relocation
trampoline, breaking earlycon in the kexec'd kernel.

Selftest support (patches 5-7)
-------------------------------
Patch 5 adds loongarch.conf and extends vmtest.sh to recognise
loongarch64 as a build target.  QEMU's LoongArch virt machine is
FDT-only (no ACPI), so 'earlycon' must appear on the kernel cmdline or
the console UART is never discovered and the test log stays empty.

Patch 6 disables SERIO_I8042 and its dependents in the QEMU_KCONFIG
fragment.  QEMU's LoongArch virt machine has no i8042 controller; the
fallback port probe hits a page fault on the memory-mapped I/O range and
panics before reaching userspace.

Patch 7 polls the serial output for the test verdict and kills QEMU once
it appears.  QEMU provides no EFI runtime services on LoongArch, so
machine_restart() falls through to an infinite idle loop and QEMU never
exits after kexec.


George Guo (7):
  LoongArch: Add KHO basic support
  LoongArch: kho: strip stale kho_handover= from reused cmdline
  LoongArch: Add missing linux/mm.h include in asm/io.h
  LoongArch: kexec: avoid overwriting QEMU's machine FDT at 0x100000
  selftests/kho: add LoongArch vmtest support
  selftests/kho: LoongArch: disable PS/2 input devices for QEMU virt
  selftests/kho: handle QEMU not exiting after kexec on LoongArch

 arch/loongarch/Kconfig                     |  3 ++
 arch/loongarch/include/asm/io.h            |  1 +
 arch/loongarch/kernel/machine_kexec.c      |  9 +++-
 arch/loongarch/kernel/machine_kexec_file.c | 57 ++++++++++++++++++++++
 arch/loongarch/kernel/setup.c              | 27 ++++++++++
 tools/testing/selftests/kho/loongarch.conf | 10 ++++
 tools/testing/selftests/kho/vmtest.sh      | 38 ++++++++++++---
 7 files changed, 135 insertions(+), 10 deletions(-)
 create mode 100644 tools/testing/selftests/kho/loongarch.conf

-- 
2.25.1

[PATCH 1/7] LoongArch: Add KHO basic support

[George Guo]

From: George Guo <guodongtai@kylinos.cn>

Enable Kexec Handover on LoongArch64:

- Kconfig: select ARCH_SUPPORTS_KEXEC_HANDOVER for 64BIT
- machine_kexec_file: add cmdline_add_kho() to pass the KHO FDT and
  scratch buffer addresses to the next kernel via the "kho_handover="
  command-line parameter
- setup: parse "kho_handover=" early and call kho_populate() to hand
  memory regions to the KHO core

Co-developed-by: Kexin Liu <liukexin@kylinos.cn>
Signed-off-by: Kexin Liu <liukexin@kylinos.cn>
Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
 arch/loongarch/Kconfig                     |  3 +++
 arch/loongarch/kernel/machine_kexec_file.c | 22 ++++++++++++++++++
 arch/loongarch/kernel/setup.c              | 27 ++++++++++++++++++++++
 3 files changed, 52 insertions(+)

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 606597da46b8..d494418545f5 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -684,6 +684,9 @@ config ARCH_SUPPORTS_KEXEC
 config ARCH_SUPPORTS_KEXEC_FILE
 	def_bool 64BIT
 
+config ARCH_SUPPORTS_KEXEC_HANDOVER
+	def_bool 64BIT
+
 config ARCH_SELECTS_KEXEC_FILE
 	def_bool 64BIT
 	depends on KEXEC_FILE
diff --git a/arch/loongarch/kernel/machine_kexec_file.c b/arch/loongarch/kernel/machine_kexec_file.c
index 5584b798ba46..ddf4d0e0e7fd 100644
--- a/arch/loongarch/kernel/machine_kexec_file.c
+++ b/arch/loongarch/kernel/machine_kexec_file.c
@@ -55,6 +55,24 @@ static void cmdline_add_initrd(struct kimage *image, unsigned long *cmdline_tmpl
 	*cmdline_tmplen += initrd_strlen;
 }
 
+#ifdef CONFIG_KEXEC_HANDOVER
+/* Add "kho_handover=<fdt_size>@<fdt_addr>,<scratch_size>@<scratch_addr>" to cmdline. */
+static void cmdline_add_kho(struct kimage *image, unsigned long *cmdline_tmplen,
+			    char *modified_cmdline)
+{
+	int n;
+
+	if (!image->kho.fdt || !image->kho.scratch)
+		return;
+
+	n = sprintf(modified_cmdline + *cmdline_tmplen,
+	    "kho_handover=0x%llx@0x%llx,0x%lx@0x%llx ",
+	    (u64)PAGE_SIZE,               image->kho.fdt,
+	    image->kho.scratch->bufsz,    (u64)image->kho.scratch->mem);
+	*cmdline_tmplen += n;
+}
+#endif
+
 #ifdef CONFIG_CRASH_DUMP
 
 static int prepare_elf_headers(void **addr, unsigned long *sz)
@@ -220,6 +238,10 @@ int load_other_segments(struct kimage *image,
 		cmdline_add_initrd(image, &cmdline_tmplen, modified_cmdline, initrd_load_addr);
 	}
 
+#ifdef CONFIG_KEXEC_HANDOVER
+	cmdline_add_kho(image, &cmdline_tmplen, modified_cmdline);
+#endif
+
 	if (cmdline_len + cmdline_tmplen > COMMAND_LINE_SIZE) {
 		pr_err("Appending command line exceeds COMMAND_LINE_SIZE\n");
 		ret = -EINVAL;
diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
index 839b23edee87..5934ba6f13e3 100644
--- a/arch/loongarch/kernel/setup.c
+++ b/arch/loongarch/kernel/setup.c
@@ -48,6 +48,7 @@
 #include <asm/setup.h>
 #include <asm/time.h>
 #include <asm/unwind.h>
+#include <linux/kexec_handover.h>
 
 #define SMBIOS_BIOSSIZE_OFFSET		0x09
 #define SMBIOS_BIOSEXTERN_OFFSET	0x13
@@ -227,6 +228,32 @@ static int __init early_parse_mem(char *p)
 }
 early_param("mem", early_parse_mem);
 
+#ifdef CONFIG_KEXEC_HANDOVER
+static int __init early_parse_kho(char *p)
+{
+	phys_addr_t fdt_addr, scratch_addr;
+	u64 fdt_size, scratch_size;
+
+	if (!p)
+		return -EINVAL;
+
+	fdt_size = memparse(p, &p);
+	if (*p++ != '@')
+		return -EINVAL;
+	fdt_addr = memparse(p, &p);
+	if (*p++ != ',')
+		return -EINVAL;
+	scratch_size = memparse(p, &p);
+	if (*p++ != '@')
+		return -EINVAL;
+	scratch_addr = memparse(p, &p);
+
+	kho_populate(fdt_addr, fdt_size, scratch_addr, scratch_size);
+	return 0;
+}
+early_param("kho_handover", early_parse_kho);
+#endif
+
 static void __init arch_reserve_vmcore(void)
 {
 #ifdef CONFIG_PROC_VMCORE
-- 
2.25.1

[PATCH 2/7] LoongArch: kho: strip stale kho_handover= from reused cmdline

[George Guo]

From: George Guo <guodongtai@kylinos.cn>

When kexec is invoked with --reuse-cmdline after a liveupdate boot, the
running kernel's command line already contains a kho_handover= parameter
from the previous kexec load.  load_other_segments() prepends a fresh
kho_handover= for the new handover FDT but then appends the original
cmdline verbatim, resulting in two kho_handover= entries:

  kho_handover=0x4000@<new_fdt>,... kho_handover=0x4000@<stale_fdt>,...

early_param() calls early_parse_kho() for each occurrence in order, so
kho_populate() is invoked twice and the second call overwrites the first
with the stale FDT address.  The stale address no longer holds a valid
KHO FDT, causing __kho_radix_walk_tree() to dereference a garbage
pointer and panic early in mm_core_init().

Fix this by adding the new kho_handover= to the cmdline prefix first,
then stripping any stale kho_handover= tokens from the appended original
cmdline portion, so only the freshly generated entry survives.

Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
 arch/loongarch/kernel/machine_kexec_file.c | 35 ++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/arch/loongarch/kernel/machine_kexec_file.c b/arch/loongarch/kernel/machine_kexec_file.c
index ddf4d0e0e7fd..ffaedd055e62 100644
--- a/arch/loongarch/kernel/machine_kexec_file.c
+++ b/arch/loongarch/kernel/machine_kexec_file.c
@@ -71,6 +71,37 @@ static void cmdline_add_kho(struct kimage *image, unsigned long *cmdline_tmplen,
 	    image->kho.scratch->bufsz,    (u64)image->kho.scratch->mem);
 	*cmdline_tmplen += n;
 }
+
+/*
+ * Remove all "kho_handover=..." tokens from cmdline.  Needed when
+ * --reuse-cmdline is used: the running kernel's cmdline already carries a
+ * stale kho_handover= from the previous kexec load; without removal the new
+ * kernel sees two entries and kho_populate() ends up using the wrong (stale)
+ * FDT address.
+ */
+static void cmdline_remove_kho(char *cmdline)
+{
+	const char *key = "kho_handover=";
+	size_t key_len = strlen(key);
+	char *p = cmdline;
+
+	while ((p = strstr(p, key)) != NULL) {
+		char *start = p;
+		char *end;
+
+		/* Only match at a token boundary */
+		if (start != cmdline && *(start - 1) != ' ') {
+			p += key_len;
+			continue;
+		}
+		end = start + key_len;
+		while (*end && *end != ' ')
+			end++;
+		while (*end == ' ')
+			end++;
+		memmove(start, end, strlen(end) + 1);
+	}
+}
 #endif
 
 #ifdef CONFIG_CRASH_DUMP
@@ -249,6 +280,10 @@ int load_other_segments(struct kimage *image,
 	}
 
 	memcpy(modified_cmdline + cmdline_tmplen, cmdline, cmdline_len);
+#ifdef CONFIG_KEXEC_HANDOVER
+	/* Strip stale kho_handover= that --reuse-cmdline may have carried over */
+	cmdline_remove_kho(modified_cmdline + cmdline_tmplen);
+#endif
 	cmdline = modified_cmdline;
 	image->arch.cmdline_ptr = (unsigned long)cmdline;
 
-- 
2.25.1

[PATCH 3/7] LoongArch: Add missing linux/mm.h include in asm/io.h

[George Guo]

From: George Guo <guodongtai@kylinos.cn>

When CONFIG_KFENCE is enabled, the virt_to_phys() and phys_to_virt()
macros in arch/loongarch/include/asm/io.h expand to use offset_in_page()
and page_address(), both of which are declared in <linux/mm.h>.

Without this include, any translation unit that includes <asm/io.h> and
expands these macros with CONFIG_KFENCE=y will fail to build. This was
observed when building kernel/liveupdate/luo_session.c with
CONFIG_KFENCE=y:

  asm/io.h: error: implicit declaration of function 'offset_in_page'
  asm/io.h: error: implicit declaration of function 'page_address'

Add the missing include to fix these build errors.

Fixes: 0ca84aeaee15 ("LoongArch: Make {virt, phys, page, pfn} translation work with KFENCE")
Co-developed-by: Kexin Liu <liukexin@kylinos.cn>
Signed-off-by: Kexin Liu <liukexin@kylinos.cn>
Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
 arch/loongarch/include/asm/io.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/loongarch/include/asm/io.h b/arch/loongarch/include/asm/io.h
index 0130185e0349..7ff4aa72a34a 100644
--- a/arch/loongarch/include/asm/io.h
+++ b/arch/loongarch/include/asm/io.h
@@ -13,6 +13,7 @@
 #include <asm/page.h>
 #include <asm/pgtable-bits.h>
 #include <asm/string.h>
+#include <linux/mm.h>
 
 extern void __init __iomem *early_ioremap(phys_addr_t phys_addr, unsigned long size);
 extern void __init early_iounmap(void __iomem *addr, unsigned long size);
-- 
2.25.1

[PATCH 4/7] LoongArch: kexec: avoid overwriting QEMU's machine FDT at 0x100000

[George Guo]

From: George Guo <guodongtai@kylinos.cn>

QEMU places its machine FDT at physical address 0x100000 when booting
with '-kernel'.  KEXEC_CONTROL_CODE was defined at the same address, so
machine_kexec_prepare() overwrites the FDT with the relocation trampoline
before jumping to the new kernel.

The kexec'd kernel's fdt_setup() reads the FDT pointer from the EFI
config table (FDTPTR = 0x100000) and finds trampoline code instead of a
valid FDT, so earlycon auto-detection fails and the second kernel boots
silently with no console output.

Move KEXEC_CONTROL_CODE to 0x180000, which is still within the first 2MB
reserved by memblock_init() and does not conflict with the QEMU FDT.

Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
 arch/loongarch/kernel/machine_kexec.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/loongarch/kernel/machine_kexec.c b/arch/loongarch/kernel/machine_kexec.c
index d7fafda1d541..44df7dbd3de5 100644
--- a/arch/loongarch/kernel/machine_kexec.c
+++ b/arch/loongarch/kernel/machine_kexec.c
@@ -21,8 +21,13 @@
 #include <asm/cacheflush.h>
 #include <asm/page.h>
 
-/* 0x100000 ~ 0x200000 is safe */
-#define KEXEC_CONTROL_CODE	TO_CACHE(0x100000UL)
+/*
+ * Both addresses are within the first 2MB which is always reserved by
+ * memblock_init().  Avoid 0x100000 because QEMU places its machine FDT
+ * there when using '-kernel'; overwriting it silences earlycon in the
+ * kexec'd kernel.
+ */
+#define KEXEC_CONTROL_CODE	TO_CACHE(0x180000UL)
 #define KEXEC_CMDLINE_ADDR	TO_CACHE(0x108000UL)
 
 static unsigned long reboot_code_buffer;
-- 
2.25.1

[PATCH 5/7] selftests/kho: add LoongArch vmtest support

[George Guo]

From: George Guo <guodongtai@kylinos.cn>

Add loongarch.conf to configure QEMU's LoongArch virt machine with a
la464 CPU, enable the 8250 serial console, and set the kernel image
to vmlinux.efi. Extend vmtest.sh to recognize loongarch64 as a
supported target and map it to the 'loongarch' kernel arch name.

QEMU's LoongArch virt machine provides no ACPI tables and relies on
FDT to describe hardware. Without 'earlycon' on the kernel command
line, the FDT is not scanned for a console UART, no output reaches
the console, and vmtest.sh's console log stays empty causing the test
to always fail. Add 'earlycon' to KERNEL_CMDLINE in loongarch.conf
to fix this.

Co-developed-by: Kexin Liu <liukexin@kylinos.cn>
Signed-off-by: Kexin Liu <liukexin@kylinos.cn>
Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
 tools/testing/selftests/kho/loongarch.conf | 7 +++++++
 tools/testing/selftests/kho/vmtest.sh      | 3 ++-
 2 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/kho/loongarch.conf

diff --git a/tools/testing/selftests/kho/loongarch.conf b/tools/testing/selftests/kho/loongarch.conf
new file mode 100644
index 000000000000..b0551e0c2d77
--- /dev/null
+++ b/tools/testing/selftests/kho/loongarch.conf
@@ -0,0 +1,7 @@
+QEMU_CMD="qemu-system-loongarch64 -M virt -cpu la464"
+QEMU_KCONFIG="
+CONFIG_SERIAL_8250=y
+CONFIG_SERIAL_8250_CONSOLE=y
+"
+KERNEL_IMAGE="vmlinux.efi"
+KERNEL_CMDLINE="console=ttyS0 earlycon"
diff --git a/tools/testing/selftests/kho/vmtest.sh b/tools/testing/selftests/kho/vmtest.sh
index 49fdac8e8b15..a6ae9ac09595 100755
--- a/tools/testing/selftests/kho/vmtest.sh
+++ b/tools/testing/selftests/kho/vmtest.sh
@@ -21,7 +21,7 @@ Options:
 	-d)	path to the kernel build directory
 	-j)	number of jobs for compilation, similar to -j in make
 	-t)	run test for target_arch, requires CROSS_COMPILE set
-		supported targets: aarch64, x86_64
+		supported targets: aarch64, x86_64, loongarch64
 	-h)	display this help
 EOF
 }
@@ -123,6 +123,7 @@ function target_to_arch() {
 	case $target in
 	     aarch64) echo "arm64" ;;
 	     x86_64) echo "x86" ;;
+	     loongarch64) echo "loongarch" ;;
 	     *) skip "architecture $target is not supported"
 	esac
 }
-- 
2.25.1

[PATCH 6/7] selftests/kho: LoongArch: disable PS/2 input devices for QEMU virt

[George Guo]

From: George Guo <guodongtai@kylinos.cn>

QEMU's LoongArch virt machine has no i8042 PS/2 controller.  When PNP
detection finds nothing, i8042_init() falls back to probing the ports
directly.  On LoongArch the I/O ports are memory-mapped, and the i8042
port addresses are not backed by any device on the virt machine, so
i8042_flush() takes a page fault and the kernel panics:

  i8042: PNP: No PS/2 controller found.
  i8042: Probing ports directly.
  CPU 0 Unable to handle kernel paging request at virtual address ffff800000008064
  ERA: i8042_flush+0x50/0x198
   RA: i8042_init+0x2a8/0x35c
  Kernel panic - not syncing: Attempted to kill init!

Disable SERIO_I8042 and its dependents (KEYBOARD_ATKBD, MOUSE_PS2) in
the QEMU_KCONFIG fragment to prevent the driver from being built.

Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
 tools/testing/selftests/kho/loongarch.conf | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/testing/selftests/kho/loongarch.conf b/tools/testing/selftests/kho/loongarch.conf
index b0551e0c2d77..0145cb49e5b2 100644
--- a/tools/testing/selftests/kho/loongarch.conf
+++ b/tools/testing/selftests/kho/loongarch.conf
@@ -2,6 +2,9 @@ QEMU_CMD="qemu-system-loongarch64 -M virt -cpu la464"
 QEMU_KCONFIG="
 CONFIG_SERIAL_8250=y
 CONFIG_SERIAL_8250_CONSOLE=y
+# CONFIG_KEYBOARD_ATKBD is not set
+# CONFIG_MOUSE_PS2 is not set
+# CONFIG_SERIO_I8042 is not set
 "
 KERNEL_IMAGE="vmlinux.efi"
 KERNEL_CMDLINE="console=ttyS0 earlycon"
-- 
2.25.1

[PATCH 7/7] selftests/kho: handle QEMU not exiting after kexec on LoongArch

[George Guo]

From: George Guo <guodongtai@kylinos.cn>

On LoongArch, QEMU provides only a minimal EFI stub with no runtime
services and no ACPI tables, so machine_restart() falls through to
its infinite idle loop and QEMU never exits after kexec.

Poll the serial output for the test verdict and kill QEMU once
it appears, rather than waiting for QEMU to exit naturally.

Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
 tools/testing/selftests/kho/vmtest.sh | 35 +++++++++++++++++++++------
 1 file changed, 28 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/kho/vmtest.sh b/tools/testing/selftests/kho/vmtest.sh
index a6ae9ac09595..3cb9674e4475 100755
--- a/tools/testing/selftests/kho/vmtest.sh
+++ b/tools/testing/selftests/kho/vmtest.sh
@@ -103,16 +103,37 @@ function run_qemu() {
 	local qemu_cmd=$1
 	local cmdline=$2
 	local kernel=$3
+	local arch=$4
 	local serial="$tmp_dir/qemu.serial"
 
 	cmdline="$cmdline kho=on panic=-1"
 
-	$qemu_cmd -m 1G -smp 2 -no-reboot -nographic -nodefaults \
-		  -accel kvm -accel hvf -accel tcg  \
-		  -serial file:"$serial" \
-		  -append "$cmdline" \
-		  -kernel "$kernel" \
-		  -initrd "$initrd"
+	local qemu_args=(
+		-m 1G -smp 2 -no-reboot -nographic -nodefaults
+		-accel kvm -accel hvf -accel tcg
+		-serial file:"$serial"
+		-append "$cmdline"
+		-kernel "$kernel"
+		-initrd "$initrd"
+	)
+
+	# On LoongArch, EFI runtime services are unavailable after kexec so
+	# machine_restart() hangs and QEMU never exits on its own.  Run QEMU
+	# in the background, poll for the test result, then kill it.
+	if [[ "$arch" == "loongarch" ]]; then
+		$qemu_cmd "${qemu_args[@]}" &
+		local qemu_pid=$!
+		local timeout=100
+		while ((timeout-- > 0)); do
+			grep -q "KHO restore succeeded\|KHO restore failed" \
+				"$serial" 2>/dev/null && break
+			sleep 1
+		done
+		kill "$qemu_pid" 2>/dev/null
+		wait "$qemu_pid" 2>/dev/null || true
+	else
+		$qemu_cmd "${qemu_args[@]}"
+	fi
 
 	grep "KHO restore succeeded" "$serial" &> /dev/null || fail "KHO failed"
 }
@@ -179,7 +200,7 @@ function main() {
 	local kernel="$build_dir/arch/$arch/boot/$KERNEL_IMAGE"
 	mkinitrd "$kernel"
 
-	run_qemu "$QEMU_CMD" "$KERNEL_CMDLINE" "$kernel"
+	run_qemu "$QEMU_CMD" "$KERNEL_CMDLINE" "$kernel" "$arch"
 
 	ktap_test_pass "KHO succeeded"
 }
-- 
2.25.1

Re: [PATCH 0/7] LoongArch: add KHO support and selftests

[Mike Rapoport]

On Mon, 25 May 2026 14:28:03 +0800, George Guo <dongtai.guo@linux.dev> wrote:

Hi,

> [...]
> 
> Bug fixes (patches 3-4)
> ------------------------
> Patch 3 fixes a build failure with CONFIG_KFENCE=y: virt_to_phys() and
> phys_to_virt() in asm/io.h expand to use offset_in_page() and
> page_address(), which require <linux/mm.h> that was not included.

This fix looks unrelated to KHO, it makes sense to send it as a separate
patch.

> 
> Patch 4 moves KEXEC_CONTROL_CODE from 0x100000 to 0x180000.  QEMU
> places its machine FDT at 0x100000 when booting with '-kernel'; the
> previous placement silently overwrote the FDT with the relocation

And I believe that patch 2 and patch 4 can be folded into patch 1 so
that addition of KHO support will be a single patch.

> trampoline, breaking earlycon in the kexec'd kernel.
> 
> Selftest support (patches 5-7)
> -------------------------------
> Patch 5 adds loongarch.conf and extends vmtest.sh to recognise
> loongarch64 as a build target.  QEMU's LoongArch virt machine is
> FDT-only (no ACPI), so 'earlycon' must appear on the kernel cmdline or
> the console UART is never discovered and the test log stays empty.
> 
> Patch 6 disables SERIO_I8042 and its dependents in the QEMU_KCONFIG
> fragment.  QEMU's LoongArch virt machine has no i8042 controller; the
> fallback port probe hits a page fault on the memory-mapped I/O range and
> panics before reaching userspace.

This should be folded into patch 5 for sure.

> 
> Patch 7 polls the serial output for the test verdict and kills QEMU once
> it appears.  QEMU provides no EFI runtime services on LoongArch, so
> machine_restart() falls through to an infinite idle loop and QEMU never
> exits after kexec.

And since without this selftest would hang on loongarch, the timeout
handing should be folded into patch 5.

In general, the rationale when adding new features is to make sure that
after each patch there are no regressions and the new functionality
either works or cannot be enabled until completely implemented.

-- 
Sincerely yours,
Mike.

Re: [PATCH 7/7] selftests/kho: handle QEMU not exiting after kexec on LoongArch

[Mike Rapoport]

On Mon, 25 May 2026 14:28:10 +0800, George Guo <dongtai.guo@linux.dev> wrote:
> diff --git a/tools/testing/selftests/kho/vmtest.sh b/tools/testing/selftests/kho/vmtest.sh
> index a6ae9ac09595..3cb9674e4475 100755
> --- a/tools/testing/selftests/kho/vmtest.sh
> +++ b/tools/testing/selftests/kho/vmtest.sh
> @@ -103,16 +103,37 @@ function run_qemu() {
>  	local qemu_cmd=$1
>  	local cmdline=$2
>  	local kernel=$3
> +	local arch=$4
>  	local serial="$tmp_dir/qemu.serial"
>  
>  	cmdline="$cmdline kho=on panic=-1"
>  
> -	$qemu_cmd -m 1G -smp 2 -no-reboot -nographic -nodefaults \

Just make it 

	timeout 100 $qemu_cmd ...

for all architectures.

-- 
Sincerely yours,
Mike.

Re: [PATCH 0/7] LoongArch: add KHO support and selftests

[Huacai Chen]

Hi, Mike,

On Mon, May 25, 2026 at 3:48 PM Mike Rapoport <rppt@kernel.org> wrote:
>
> On Mon, 25 May 2026 14:28:03 +0800, George Guo <dongtai.guo@linux.dev> wrote:
>
> Hi,
>
> > [...]
> >
> > Bug fixes (patches 3-4)
> > ------------------------
> > Patch 3 fixes a build failure with CONFIG_KFENCE=y: virt_to_phys() and
> > phys_to_virt() in asm/io.h expand to use offset_in_page() and
> > page_address(), which require <linux/mm.h> that was not included.
>
> This fix looks unrelated to KHO, it makes sense to send it as a separate
> patch.
He tried, but it causes new problems, but I agree this patch has
nothing to do with KHO.
https://lore.kernel.org/loongarch/202605211925.DbDvQ6ii-lkp@intel.com/T/#t

>
> >
> > Patch 4 moves KEXEC_CONTROL_CODE from 0x100000 to 0x180000.  QEMU
> > places its machine FDT at 0x100000 when booting with '-kernel'; the
> > previous placement silently overwrote the FDT with the relocation
>
> And I believe that patch 2 and patch 4 can be folded into patch 1 so
> that addition of KHO support will be a single patch.
Patch 2 should be folded, but Patch 4 can be separate, because it
should be backported.

>
> > trampoline, breaking earlycon in the kexec'd kernel.
> >
> > Selftest support (patches 5-7)
> > -------------------------------
> > Patch 5 adds loongarch.conf and extends vmtest.sh to recognise
> > loongarch64 as a build target.  QEMU's LoongArch virt machine is
> > FDT-only (no ACPI), so 'earlycon' must appear on the kernel cmdline or
> > the console UART is never discovered and the test log stays empty.
> >
> > Patch 6 disables SERIO_I8042 and its dependents in the QEMU_KCONFIG
> > fragment.  QEMU's LoongArch virt machine has no i8042 controller; the
> > fallback port probe hits a page fault on the memory-mapped I/O range and
> > panics before reaching userspace.
>
> This should be folded into patch 5 for sure.
I completely don't know why Patch 6 is needed, for normal use I8042
doesn't cause problems in virtual machines.

Huacai

>
> >
> > Patch 7 polls the serial output for the test verdict and kills QEMU once
> > it appears.  QEMU provides no EFI runtime services on LoongArch, so
> > machine_restart() falls through to an infinite idle loop and QEMU never
> > exits after kexec.
>
> And since without this selftest would hang on loongarch, the timeout
> handing should be folded into patch 5.
>
> In general, the rationale when adding new features is to make sure that
> after each patch there are no regressions and the new functionality
> either works or cannot be enabled until completely implemented.
>
> --
> Sincerely yours,
> Mike.
>

Re: [PATCH 0/7] LoongArch: add KHO support and selftests

[Mike Rapoport]

Hi,

On 2026-05-25 18:25:08+08:00, Huacai Chen wrote:
> Hi, Mike,
> 
> On Mon, May 25, 2026 at 3:48 PM Mike Rapoport <rppt@kernel.org> wrote:
> 
> > On Mon, 25 May 2026 14:28:03 +0800, George Guo <dongtai.guo@linux.dev> wrote:
> >
> > This fix looks unrelated to KHO, it makes sense to send it as a separate
> > patch.
> 
> He tried, but it causes new problems, but I agree this patch has
> nothing to do with KHO.
> https://lore.kernel.org/loongarch/202605211925.DbDvQ6ii-lkp@intel.com/T/#t
> 
> > And I believe that patch 2 and patch 4 can be folded into patch 1 so
> > that addition of KHO support will be a single patch.
> 
> Patch 2 should be folded, but Patch 4 can be separate, because it
> should be backported.

Fair enough. 
I'd suggest to move the fixes to be the first patches in the series, but
presuming this is going via loongarch tree it's up to you :)

> > This should be folded into patch 5 for sure.
> 
> I completely don't know why Patch 6 is needed, for normal use I8042
> doesn't cause problems in virtual machines.
> 
> Huacai

Re: [PATCH 1/7] LoongArch: Add KHO basic support

[Pratyush Yadav]

On Mon, May 25 2026, George Guo wrote:

> From: George Guo <guodongtai@kylinos.cn>
>
> Enable Kexec Handover on LoongArch64:
>
> - Kconfig: select ARCH_SUPPORTS_KEXEC_HANDOVER for 64BIT
> - machine_kexec_file: add cmdline_add_kho() to pass the KHO FDT and
>   scratch buffer addresses to the next kernel via the "kho_handover="
>   command-line parameter
> - setup: parse "kho_handover=" early and call kho_populate() to hand
>   memory regions to the KHO core
>
> Co-developed-by: Kexin Liu <liukexin@kylinos.cn>
> Signed-off-by: Kexin Liu <liukexin@kylinos.cn>
> Signed-off-by: George Guo <guodongtai@kylinos.cn>
> ---
>  arch/loongarch/Kconfig                     |  3 +++
>  arch/loongarch/kernel/machine_kexec_file.c | 22 ++++++++++++++++++
>  arch/loongarch/kernel/setup.c              | 27 ++++++++++++++++++++++
>  3 files changed, 52 insertions(+)
>
[...]
> diff --git a/arch/loongarch/kernel/machine_kexec_file.c b/arch/loongarch/kernel/machine_kexec_file.c
> index 5584b798ba46..ddf4d0e0e7fd 100644
> --- a/arch/loongarch/kernel/machine_kexec_file.c
> +++ b/arch/loongarch/kernel/machine_kexec_file.c
> @@ -55,6 +55,24 @@ static void cmdline_add_initrd(struct kimage *image, unsigned long *cmdline_tmpl
>  	*cmdline_tmplen += initrd_strlen;
>  }
>  
> +#ifdef CONFIG_KEXEC_HANDOVER
> +/* Add "kho_handover=<fdt_size>@<fdt_addr>,<scratch_size>@<scratch_addr>" to cmdline. */
> +static void cmdline_add_kho(struct kimage *image, unsigned long *cmdline_tmplen,
> +			    char *modified_cmdline)
> +{
> +	int n;
> +
> +	if (!image->kho.fdt || !image->kho.scratch)
> +		return;
> +
> +	n = sprintf(modified_cmdline + *cmdline_tmplen,
> +	    "kho_handover=0x%llx@0x%llx,0x%lx@0x%llx ",
> +	    (u64)PAGE_SIZE,               image->kho.fdt,
> +	    image->kho.scratch->bufsz,    (u64)image->kho.scratch->mem);
> +	*cmdline_tmplen += n;

Do you have nothing else for a bootloader to pass data to the kernel?
Passing this via the command line seems crazy... All these addresses are
now available directly to unprivileged userspace. Can't you use the
device tree like we do on ARM64?

Also, this commandline parameter isn't documented anywhere.

> +}
> +#endif
> +
>  #ifdef CONFIG_CRASH_DUMP
>  
>  static int prepare_elf_headers(void **addr, unsigned long *sz)
> @@ -220,6 +238,10 @@ int load_other_segments(struct kimage *image,
>  		cmdline_add_initrd(image, &cmdline_tmplen, modified_cmdline, initrd_load_addr);
>  	}
>  
> +#ifdef CONFIG_KEXEC_HANDOVER
> +	cmdline_add_kho(image, &cmdline_tmplen, modified_cmdline);
> +#endif
> +
>  	if (cmdline_len + cmdline_tmplen > COMMAND_LINE_SIZE) {
>  		pr_err("Appending command line exceeds COMMAND_LINE_SIZE\n");
>  		ret = -EINVAL;
> diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
> index 839b23edee87..5934ba6f13e3 100644
> --- a/arch/loongarch/kernel/setup.c
> +++ b/arch/loongarch/kernel/setup.c
> @@ -48,6 +48,7 @@
>  #include <asm/setup.h>
>  #include <asm/time.h>
>  #include <asm/unwind.h>
> +#include <linux/kexec_handover.h>
>  
>  #define SMBIOS_BIOSSIZE_OFFSET		0x09
>  #define SMBIOS_BIOSEXTERN_OFFSET	0x13
> @@ -227,6 +228,32 @@ static int __init early_parse_mem(char *p)
>  }
>  early_param("mem", early_parse_mem);
>  
> +#ifdef CONFIG_KEXEC_HANDOVER
> +static int __init early_parse_kho(char *p)
> +{
> +	phys_addr_t fdt_addr, scratch_addr;
> +	u64 fdt_size, scratch_size;
> +
> +	if (!p)
> +		return -EINVAL;
> +
> +	fdt_size = memparse(p, &p);
> +	if (*p++ != '@')

Can you please wrap these in parenthesis? I am too dumb to remember all
the precedence rules and this immediately makes me question whether we
are doing (*p)++ or *(p++).

> +		return -EINVAL;
> +	fdt_addr = memparse(p, &p);
> +	if (*p++ != ',')
> +		return -EINVAL;
> +	scratch_size = memparse(p, &p);
> +	if (*p++ != '@')
> +		return -EINVAL;
> +	scratch_addr = memparse(p, &p);
> +
> +	kho_populate(fdt_addr, fdt_size, scratch_addr, scratch_size);
> +	return 0;
> +}
> +early_param("kho_handover", early_parse_kho);
> +#endif
> +
>  static void __init arch_reserve_vmcore(void)
>  {
>  #ifdef CONFIG_PROC_VMCORE

-- 
Regards,
Pratyush Yadav

Re: [PATCH 2/7] LoongArch: kho: strip stale kho_handover= from reused cmdline

[Pratyush Yadav]

On Mon, May 25 2026, George Guo wrote:

> From: George Guo <guodongtai@kylinos.cn>
>
> When kexec is invoked with --reuse-cmdline after a liveupdate boot, the
> running kernel's command line already contains a kho_handover= parameter
> from the previous kexec load.  load_other_segments() prepends a fresh
> kho_handover= for the new handover FDT but then appends the original
> cmdline verbatim, resulting in two kho_handover= entries:
>
>   kho_handover=0x4000@<new_fdt>,... kho_handover=0x4000@<stale_fdt>,...
>
> early_param() calls early_parse_kho() for each occurrence in order, so
> kho_populate() is invoked twice and the second call overwrites the first
> with the stale FDT address.  The stale address no longer holds a valid
> KHO FDT, causing __kho_radix_walk_tree() to dereference a garbage
> pointer and panic early in mm_core_init().
>
> Fix this by adding the new kho_handover= to the cmdline prefix first,
> then stripping any stale kho_handover= tokens from the appended original
> cmdline portion, so only the freshly generated entry survives.
>
> Signed-off-by: George Guo <guodongtai@kylinos.cn>
> ---
>  arch/loongarch/kernel/machine_kexec_file.c | 35 ++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
>
> diff --git a/arch/loongarch/kernel/machine_kexec_file.c b/arch/loongarch/kernel/machine_kexec_file.c
> index ddf4d0e0e7fd..ffaedd055e62 100644
> --- a/arch/loongarch/kernel/machine_kexec_file.c
> +++ b/arch/loongarch/kernel/machine_kexec_file.c
> @@ -71,6 +71,37 @@ static void cmdline_add_kho(struct kimage *image, unsigned long *cmdline_tmplen,
>  	    image->kho.scratch->bufsz,    (u64)image->kho.scratch->mem);
>  	*cmdline_tmplen += n;
>  }
> +
> +/*
> + * Remove all "kho_handover=..." tokens from cmdline.  Needed when
> + * --reuse-cmdline is used: the running kernel's cmdline already carries a
> + * stale kho_handover= from the previous kexec load; without removal the new
> + * kernel sees two entries and kho_populate() ends up using the wrong (stale)
> + * FDT address.
> + */
> +static void cmdline_remove_kho(char *cmdline)
> +{
> +	const char *key = "kho_handover=";
> +	size_t key_len = strlen(key);
> +	char *p = cmdline;
> +
> +	while ((p = strstr(p, key)) != NULL) {
> +		char *start = p;
> +		char *end;
> +
> +		/* Only match at a token boundary */
> +		if (start != cmdline && *(start - 1) != ' ') {
> +			p += key_len;
> +			continue;
> +		}
> +		end = start + key_len;
> +		while (*end && *end != ' ')
> +			end++;
> +		while (*end == ' ')
> +			end++;
> +		memmove(start, end, strlen(end) + 1);
> +	}
> +}

Ugh, modifying the commandline supplied by userspace feels odd... Can
you at all do this via device tree?

If not, would it make more sense to reject kexec_load if command line
has kho_handover= and teach kexec-tools to strip it on its side?

>  #endif
>  
>  #ifdef CONFIG_CRASH_DUMP
> @@ -249,6 +280,10 @@ int load_other_segments(struct kimage *image,
>  	}
>  
>  	memcpy(modified_cmdline + cmdline_tmplen, cmdline, cmdline_len);
> +#ifdef CONFIG_KEXEC_HANDOVER
> +	/* Strip stale kho_handover= that --reuse-cmdline may have carried over */
> +	cmdline_remove_kho(modified_cmdline + cmdline_tmplen);
> +#endif
>  	cmdline = modified_cmdline;
>  	image->arch.cmdline_ptr = (unsigned long)cmdline;

-- 
Regards,
Pratyush Yadav