在 2020/3/5 5:44, Scott Wood 写道:
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?
kernstart_virt_addr is in the data section. At the early boot we only
have a 64M tlb mapping. For the 32-bit I limited the kernel in a
64M-aligned region so that we can always get kernstart_virt_addr. But
for the 64-bit the kernel is bigger and not suitable to limit it in a
64M-aligned region.
So if we use kernstart_virt_addr and the kernel is randomized like below
, the secondary cpus will not boot up:
+------------+------------+
| 64M | 64M |
+------------+------------+
^ ^
| kernel |
^
kernstart_virt_addr
So I have to put the kernel offset in the first 64K along with the init
text.
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?
It does not need to be at a fixed address. I just want to keep
consistent and stay along with __run_at_load.
/* 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?
I'm not sure if relocat works for fixed symbols. I will have a test and
swith to reference them by symbols if it works fine.
+ /* Setup flat device-tree pointer */
+ initial_boot_params = dt_ptr;
+#endif
Why does 64-bit need this but 32-bit doesn't?
32-bit called early_get_first_memblock_info() very early which
implicitly setup the device-tree pointer.
-Scott
.
