Re: [PATCH 03/15] kexec: Add Kexec HandOver (KHO) generation helpers

2023-12-13 Thread Alexander Graf 


On 13.12.23 19:36, Stanislav Kinsburskii wrote:

On Wed, Dec 13, 2023 at 12:04:40AM +, Alexander Graf wrote:

+int register_kho_notifier(struct notifier_block *nb)
+{
+ return blocking_notifier_chain_register(_head, nb);
+}
+EXPORT_SYMBOL_GPL(register_kho_notifier);
+
+int unregister_kho_notifier(struct notifier_block *nb)
+{
+ return blocking_notifier_chain_unregister(_head, nb);
+}
+EXPORT_SYMBOL_GPL(unregister_kho_notifier);
+
+bool kho_is_active(void)
+{
+ return kho.active;
+}
+EXPORT_SYMBOL_GPL(kho_is_active);
+

Why should these helpers be restricted to GPL code?



That's a simple one: Everything should be EXPORT_SYMBOL_GPL by default. 
You need to have really good reasons to export anything for non-GPL 
modules. I don't have a good reason for them, so it's GPL only :)



Alex





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Re: [PATCH 03/15] kexec: Add Kexec HandOver (KHO) generation helpers

2023-12-13 Thread Stanislav Kinsburskii 
On Wed, Dec 13, 2023 at 12:04:40AM +, Alexander Graf wrote:
> +int register_kho_notifier(struct notifier_block *nb)
> +{
> + return blocking_notifier_chain_register(_head, nb);
> +}
> +EXPORT_SYMBOL_GPL(register_kho_notifier);
> +
> +int unregister_kho_notifier(struct notifier_block *nb)
> +{
> + return blocking_notifier_chain_unregister(_head, nb);
> +}
> +EXPORT_SYMBOL_GPL(unregister_kho_notifier);
> +
> +bool kho_is_active(void)
> +{
> + return kho.active;
> +}
> +EXPORT_SYMBOL_GPL(kho_is_active);
> +

Why should these helpers be restricted to GPL code?

[PATCH 03/15] kexec: Add Kexec HandOver (KHO) generation helpers

2023-12-12 Thread Alexander Graf 
This patch adds the core infrastructure to generate Kexec HandOver
metadata. Kexec HandOver is a mechanism that allows Linux to preserve
state - arbitrary properties as well as memory locations - across kexec.

It does so using 3 concepts:

  1) Device Tree - Every KHO kexec carries a KHO specific flattened
 device tree blob that describes the state of the system. Device
 drivers can register to KHO to serialize their state before kexec.

  2) Mem cache - A memblocks like structure that contains full page
 ranges of reservations. These can not be part of the architectural
 reservations, because they differ on every kexec.

  3) Scratch Region - A CMA region that we allocate in the first kernel.
 CMA gives us the guarantee that no handover pages land in that
 region, because handover pages must be at a static physical memory
 location. We use this region as the place to load future kexec
 images into which then won't collide with any handover data.

Signed-off-by: Alexander Graf 
---
 Documentation/ABI/testing/sysfs-kernel-kho|  53 +++
 .../admin-guide/kernel-parameters.txt |  10 +
 MAINTAINERS   |   1 +
 include/linux/kexec.h |  24 ++
 include/uapi/linux/kexec.h|   6 +
 kernel/Makefile   |   1 +
 kernel/kexec_kho_out.c| 316 ++
 7 files changed, 411 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-kernel-kho
 create mode 100644 kernel/kexec_kho_out.c

diff --git a/Documentation/ABI/testing/sysfs-kernel-kho 
b/Documentation/ABI/testing/sysfs-kernel-kho
new file mode 100644
index ..f69e7b81a337
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-kernel-kho
@@ -0,0 +1,53 @@
+What:  /sys/kernel/kho/active
+Date:  December 2023
+Contact:   Alexander Graf 
+Description:
+   Kexec HandOver (KHO) allows Linux to transition the state of
+   compatible drivers into the next kexec'ed kernel. To do so,
+   device drivers will serialize their current state into a DT.
+   While the state is serialized, they are unable to perform
+   any modifications to state that was serialized, such as
+   handed over memory allocations.
+
+   When this file contains "1", the system is in the transition
+   state. When contains "0", it is not. To switch between the
+   two states, echo the respective number into this file.
+
+What:  /sys/kernel/kho/dt_max
+Date:  December 2023
+Contact:   Alexander Graf 
+Description:
+   KHO needs to allocate a buffer for the DT that gets
+   generated before it knows the final size. By default, it
+   will allocate 10 MiB for it. You can write to this file
+   to modify the size of that allocation.
+
+What:  /sys/kernel/kho/scratch_len
+Date:  December 2023
+Contact:   Alexander Graf 
+Description:
+   To support continuous KHO kexecs, we need to reserve a
+   physically contiguous memory region that will always stay
+   available for future kexec allocations. This file describes
+   the length of that memory region. Kexec user space tooling
+   can use this to determine where it should place its payload
+   images.
+
+What:  /sys/kernel/kho/scratch_phys
+Date:  December 2023
+Contact:   Alexander Graf 
+Description:
+   To support continuous KHO kexecs, we need to reserve a
+   physically contiguous memory region that will always stay
+   available for future kexec allocations. This file describes
+   the physical location of that memory region. Kexec user space
+   tooling can use this to determine where it should place its
+   payload images.
+
+What:  /sys/kernel/kho/dt
+Date:  December 2023
+Contact:   Alexander Graf 
+Description:
+   When KHO is active, the kernel exposes the generated DT that
+   carries its current KHO state in this file. Kexec user space
+   tooling can use this as input file for the KHO payload image.
diff --git a/Documentation/admin-guide/kernel-parameters.txt 
b/Documentation/admin-guide/kernel-parameters.txt
index 51575cd31741..efeef075617e 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2504,6 +2504,16 @@
kgdbwait[KGDB] Stop kernel execution and enter the
kernel debugger at the earliest opportunity.
 
+   kho_scratch=n[KMG]  [KEXEC] Sets the size of the KHO scratch
+   region. The KHO scratch region is a physically
+   memory range that can only be used for non-kernel
+