powerpc: introduce kernstart_virt_addr to store the kernel base

Now the kernel base is a fixed value - KERNELBASE. To support KASLR, we
need a variable to store the kernel base.
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Reviewed-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Diana Craciun <diana.craciun@nxp.com>
Tested-by: Diana Craciun <diana.craciun@nxp.com>
Signed-off-by: Scott Wood <oss@buserror.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/page.h

@@ -325,6 +325,8 @@ void arch_free_page(struct page *page, int order);
 
 struct vm_area_struct;
 
+extern unsigned long kernstart_virt_addr;
+
 #include <asm-generic/memory_model.h>
 #endif /* __ASSEMBLY__ */
 #include <asm/slice.h>

arch/powerpc/mm/init-common.c

@@ -25,6 +25,8 @@ phys_addr_t memstart_addr __ro_after_init = (phys_addr_t)~0ull;
 EXPORT_SYMBOL_GPL(memstart_addr);
 phys_addr_t kernstart_addr __ro_after_init;
 EXPORT_SYMBOL_GPL(kernstart_addr);
+unsigned long kernstart_virt_addr __ro_after_init = KERNELBASE;
+EXPORT_SYMBOL_GPL(kernstart_virt_addr);
 
 static bool disable_kuep = !IS_ENABLED(CONFIG_PPC_KUEP);
 static bool disable_kuap = !IS_ENABLED(CONFIG_PPC_KUAP);