riscv: Export va_kernel_pa_offset in vmcoreinfo

Since RISC-V Linux v6.4, the commit 3335068 ("riscv: Use
PUD/P4D/PGD pages for the linear mapping") changes phys_ram_base
from the physical start of the kernel to the actual start of the DRAM.

The Crash-utility's VTOP() still uses phys_ram_base and kernel_map.virt_addr
to translate kernel virtual address, that failed the Crash with Linux v6.4 [1].

Export kernel_map.va_kernel_pa_offset in vmcoreinfo to help Crash translate
the kernel virtual address correctly.

Fixes: 3335068 ("riscv: Use PUD/P4D/PGD pages for the linear mapping")
Link: https://lore.kernel.org/linux-riscv/[email protected]/ [1]
Signed-off-by: Song Shuai <[email protected]>
Reviewed-by: Xianting Tian  <[email protected]>
Reviewed-by: Alexandre Ghiti <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Cc: [email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: Song Shuai

arch/riscv/kernel/crash_core.c

@@ -18,4 +18,6 @@ void arch_crash_save_vmcoreinfo(void)
 	vmcoreinfo_append_str("NUMBER(MODULES_END)=0x%lx\n", MODULES_END);
 #endif
 	vmcoreinfo_append_str("NUMBER(KERNEL_LINK_ADDR)=0x%lx\n", KERNEL_LINK_ADDR);
+	vmcoreinfo_append_str("NUMBER(va_kernel_pa_offset)=0x%lx\n",
+						kernel_map.va_kernel_pa_offset);
 }