On Thu, 2020-02-06 at 10:58 +0800, Jason Yan wrote: > The implementation for Freescale BookE64 is similar as BookE32. One > difference is that Freescale BookE64 set up a TLB mapping of 1G during > booting. Another difference is that ppc64 needs the kernel to be > 64K-aligned. So we can randomize the kernel in this 1G mapping and make > it 64K-aligned. This can save some code to creat another TLB map at > early boot. The disadvantage is that we only have about 1G/64K = 16384 > slots to put the kernel in. > > To support secondary cpu boot up, a variable __kaslr_offset was added in > first_256B section. This can help secondary cpu get the kaslr offset > before the 1:1 mapping has been setup. What specifically requires __kaslr_offset instead of using kernstart_virt_addr like 32-bit does? > > diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S > index ad79fddb974d..744624140fb8 100644 > --- a/arch/powerpc/kernel/head_64.S > +++ b/arch/powerpc/kernel/head_64.S > @@ -104,6 +104,13 @@ __secondary_hold_acknowledge: > .8byte 0x0 > > #ifdef CONFIG_RELOCATABLE > +#ifdef CONFIG_RANDOMIZE_BASE > + . = 0x58 > + .globl __kaslr_offset > +__kaslr_offset: > +DEFINE_FIXED_SYMBOL(__kaslr_offset) > + .long 0 > +#endif > /* This flag is set to 1 by a loader if the kernel should run > * at the loaded address instead of the linked address. This > * is used by kexec-tools to keep the the kdump kernel in the Why does it need to go here at a fixed address? > > /* check for a reserved-memory node and record its cell sizes */ > regions.reserved_mem = fdt_path_offset(dt_ptr, "/reserved-memory"); > @@ -363,6 +374,17 @@ notrace void __init kaslr_early_init(void *dt_ptr, > phys_addr_t size) > unsigned long offset; > unsigned long kernel_sz; > > +#ifdef CONFIG_PPC64 > + unsigned int *__kaslr_offset = (unsigned int *)(KERNELBASE + 0x58); > + unsigned int *__run_at_load = (unsigned int *)(KERNELBASE + 0x5c); Why are you referencing these by magic offset rather than by symbol? > + /* Setup flat device-tree pointer */ > + initial_boot_params = dt_ptr; > +#endif Why does 64-bit need this but 32-bit doesn't? -Scott
