Jinglin Wen <jinglin....@shingroup.cn> writes:
> According to the code logic, when the kernel is loaded to address 0,
> no copying operation should be performed, but it is currently being
> done.
>
> This patch fixes the issue where the kernel code was incorrectly
> duplicated to address 0 when booting from address 0.
>
> Signed-off-by: Jinglin Wen <jinglin....@shingroup.cn>
> ---
> arch/powerpc/kernel/head_64.S | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
Thanks for the improved change log.
The subject could probably still be clearer, maybe:
Fix unnecessary copy to 0 when kernel is booted at address 0
Looks like this was introduced by:
Fixes: b270bebd34e3 ("powerpc/64s: Run at the kernel virtual address earlier
in boot")
Cc: sta...@vger.kernel.org # v6.4+
Let me know if you think otherwise.
Just out of interest, how are you hitting this bug? AFAIK none of our
"normal" boot loaders will load the kernel at 0.
> diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
> index 4690c219bfa4..6c73551bdc50 100644
> --- a/arch/powerpc/kernel/head_64.S
> +++ b/arch/powerpc/kernel/head_64.S
> @@ -647,7 +647,9 @@ __after_prom_start:
> * Note: This process overwrites the OF exception vectors.
> */
> LOAD_REG_IMMEDIATE(r3, PAGE_OFFSET)
> - mr. r4,r26 /* In some cases the loader may */
> + tophys(r4,r26)
> + cmplwi cr0,r4,0 /* runtime base addr is zero */
> + mr r4,r26 /* In some cases the loader may */
> beq 9f /* have already put us at zero */
That is a pretty minimal fix, but I think the code would be clearer if
we just compared the source and destination addresses.
Something like the diff below. Can you confirm that works for you.
cheers
diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 4690c219bfa4..6ad1435303f9 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -647,8 +647,9 @@ __after_prom_start:
* Note: This process overwrites the OF exception vectors.
*/
LOAD_REG_IMMEDIATE(r3, PAGE_OFFSET)
- mr. r4,r26 /* In some cases the loader may */
- beq 9f /* have already put us at zero */
+ mr r4, r26 // Load the source address into r4
+ cmpld cr0, r3, r4 // Check if source == dest
+ beq 9f // If so skip the copy
li r6,0x100 /* Start offset, the first 0x100 */
/* bytes were copied earlier. */
