Lines Matching +full:linear +full:- +full:mapping +full:- +full:mode

1 .. SPDX-License-Identifier: GPL-2.0
4 RISC-V Kernel Boot Requirements and Constraints
10 This document describes what the RISC-V kernel expects from bootloaders and
14 mapping is set up.
16 Pre-kernel Requirements and Constraints
19 The RISC-V kernel expects the following of bootloaders and platform firmware:
22 --------------
24 The RISC-V kernel expects:
30 ---------
32 The RISC-V kernel expects:
37 -------------------------------------
39 The RISC-V kernel must not map any resident memory, or memory protected with
40 PMPs, in the direct mapping, so the firmware must correctly mark those regions
44 ---------------
46 The RISC-V kernel expects to be placed at a PMD boundary (2MB aligned for rv64
51 --------------------
53 The firmware can pass either a devicetree or ACPI tables to the RISC-V kernel.
64 ------------
68 - ``RISCV_BOOT_SPINWAIT``: the firmware releases all harts in the kernel, one hart
71   support older firmwares without SBI HSM extension and M-mode RISC-V kernel.
72 - ``Ordered booting``: the firmware releases only one hart that will execute the
75   booting the RISC-V kernel because it can support CPU hotplug and kexec.
78 ----
83 When booting with UEFI, the RISC-V kernel will use only the EFI memory map to
86 The UEFI firmware must parse the subnodes of the ``/reserved-memory`` devicetree
88 those subnodes (``no-map`` and ``reusable``) into their correct EFI equivalent
89 (refer to section "3.5.4 /reserved-memory and UEFI" of the devicetree
90 specification v0.4-rc1).
96 it to the RISC-V kernel in ``$a1``. The EFI stub retrieves the boot hartid using
99 - ``RISCV_EFI_BOOT_PROTOCOL`` (**preferred**).
100 - ``boot-hartid`` devicetree subnode (**deprecated**).
108 The RISC-V kernel's early boot process operates under the following constraints:
111 -----------------------
117 Virtual mapping installation
118 ----------------------------
120 The installation of the virtual mapping is done in 2 steps in the RISC-V kernel:
122 1. ``setup_vm()`` installs a temporary kernel mapping in ``early_pg_dir`` which
124    at this point. When establishing this mapping, no allocation can be done
128 2. ``setup_vm_final()`` creates the final kernel mapping in ``swapper_pg_dir``
129    and takes advantage of the discovered system memory to create the linear
130    mapping. When establishing this mapping, the kernel can allocate memory but
131    cannot access it directly (since the direct mapping is not present yet), so
136 direct mapping addresses to physical addresses, they need to know the start of
138 mapping (see ``setup_bootmem()`` function in arch/riscv/mm/init.c). Any usage of
139 those macros before the final virtual mapping is installed must be carefully
142 Devicetree mapping via fixmap
143 -----------------------------
146 by ``setup_vm()``, and used with the mapping established by
147 ``setup_vm_final()``, the RISC-V kernel uses the fixmap region to map the
151 Pre-MMU execution
152 -----------------
154 A few pieces of code need to run before even the first virtual mapping is
155 established. These are the installation of the first virtual mapping itself,
159 - ``-fno-pie``: This is needed for relocatable kernels which use ``-fPIE``,
162 - ``-mcmodel=medany``: Any access to a global symbol must be PC-relative to
164 - *all* instrumentation must also be disabled (that includes KASAN, ftrace and