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With KHO in place, let's add documentation that describes what it is and how to use it. Link: https://lkml.kernel.org/r/20250509074635.3187114-17-changyuanl@google.com Signed-off-by: Alexander Graf <graf@amazon.com> Co-developed-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Co-developed-by: Changyuan Lyu <changyuanl@google.com> Signed-off-by: Changyuan Lyu <changyuanl@google.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Anthony Yznaga <anthony.yznaga@oracle.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Ashish Kalra <ashish.kalra@amd.com> Cc: Ben Herrenschmidt <benh@kernel.crashing.org> Cc: Borislav Betkov <bp@alien8.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Woodhouse <dwmw2@infradead.org> Cc: Eric Biederman <ebiederm@xmission.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: James Gowans <jgowans@amazon.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Krzysztof Kozlowski <krzk@kernel.org> Cc: Marc Rutland <mark.rutland@arm.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Pratyush Yadav <ptyadav@amazon.de> Cc: Rob Herring <robh@kernel.org> Cc: Saravana Kannan <saravanak@google.com> Cc: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleinxer <tglx@linutronix.de> Cc: Thomas Lendacky <thomas.lendacky@amd.com> Cc: Will Deacon <will@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
81 lines
2.1 KiB
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81 lines
2.1 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0-or-later
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=======
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KHO FDT
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=======
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KHO uses the flattened device tree (FDT) container format and libfdt
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library to create and parse the data that is passed between the
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kernels. The properties in KHO FDT are stored in native format.
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It includes the physical address of an in-memory structure describing
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all preserved memory regions, as well as physical addresses of KHO users'
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own FDTs. Interpreting those sub FDTs is the responsibility of KHO users.
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KHO nodes and properties
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========================
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Property ``preserved-memory-map``
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---------------------------------
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KHO saves a special property named ``preserved-memory-map`` under the root node.
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This node contains the physical address of an in-memory structure for KHO to
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preserve memory regions across kexec.
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Property ``compatible``
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-----------------------
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The ``compatible`` property determines compatibility between the kernel
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that created the KHO FDT and the kernel that attempts to load it.
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If the kernel that loads the KHO FDT is not compatible with it, the entire
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KHO process will be bypassed.
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Property ``fdt``
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----------------
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Generally, a KHO user serialize its state into its own FDT and instructs
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KHO to preserve the underlying memory, such that after kexec, the new kernel
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can recover its state from the preserved FDT.
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A KHO user thus can create a node in KHO root tree and save the physical address
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of its own FDT in that node's property ``fdt`` .
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Examples
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========
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The following example demonstrates KHO FDT that preserves two memory
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regions created with ``reserve_mem`` kernel command line parameter::
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/dts-v1/;
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/ {
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compatible = "kho-v1";
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preserved-memory-map = <0x40be16 0x1000000>;
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memblock {
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fdt = <0x1517 0x1000000>;
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};
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};
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where the ``memblock`` node contains an FDT that is requested by the
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subsystem memblock for preservation. The FDT contains the following
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serialized data::
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/dts-v1/;
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/ {
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compatible = "memblock-v1";
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n1 {
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compatible = "reserve-mem-v1";
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start = <0xc06b 0x4000000>;
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size = <0x04 0x00>;
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};
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n2 {
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compatible = "reserve-mem-v1";
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start = <0xc067 0x4000000>;
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size = <0x04 0x00>;
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};
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};
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