riscv: kexec_file: Constrain segment placement to direct map

When kexec_file_load places segments with buf_max=ULONG_MAX and
top_down=true, they land at the highest available physical addresses.
On RISC-V the size of the linear mapping is determined by the active
VM mode: SV39 caps the direct map at roughly 128GB, while SV48/SV57
extend the range substantially further. When the installed physical
memory exceeds the direct map size of the active mode, top-down
placement puts DTB/initrd at physical addresses outside the linearly
mapped region. The kexec'd kernel cannot reach them during early
boot, triggering a page fault at memcmp in start_kernel.

Fix by constraining buf_max to PFN_PHYS(max_low_pfn), which reflects
the runtime direct map boundary for the active VM mode (SV39/SV48/
SV57). This keeps all kexec segments within the linearly mapped
region while preserving the upstream top_down allocation strategy.

Signed-off-by: Han Gao <gaohan@iscas.ac.cn>
Link: https://patch.msgid.link/20260519170641.123517-1-gaohan@iscas.ac.cn
Signed-off-by: Paul Walmsley <pjw@kernel.org>

diff --git a/arch/riscv/kernel/machine_kexec_file.c b/arch/riscv/kernel/machine_kexec_file.c
index 54e2d9552e930d4c085895baef78f3e4fb4b6c2f..59d4bbc848a896ed2a4ea52415e0b03c2ec54918 100644 (file)
--- a/arch/riscv/kernel/machine_kexec_file.c
+++ b/arch/riscv/kernel/machine_kexec_file.c
@@ -13,6 +13,7 @@
 #include <linux/libfdt.h>
 #include <linux/types.h>
 #include <linux/memblock.h>
+#include <linux/pfn.h>
 #include <linux/vmalloc.h>
 #include <asm/setup.h>
 #include <asm/insn.h>
@@ -266,7 +267,7 @@ int load_extra_segments(struct kimage *image, unsigned long kernel_start,
 
        kbuf.image = image;
        kbuf.buf_min = kernel_start + kernel_len;
-       kbuf.buf_max = ULONG_MAX;
+       kbuf.buf_max = PFN_PHYS(max_low_pfn);
 
 #ifdef CONFIG_CRASH_DUMP
        /* Add elfcorehdr */