On Wed, Jun 07, 2023 at 09:23:32AM +0200, Ard Biesheuvel wrote:
> Instead of returning to the asm calling code to invoke the trampoline,
> call it straight from the C code that sets the scene. That way, the
> struct return type is no longer needed for returning two values, and the
> call can be made conditional more cleanly in a subsequent patch.
>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> ---
> arch/x86/boot/compressed/head_64.S | 20 +++-----------
> arch/x86/boot/compressed/pgtable_64.c | 28 ++++++++------------
> 2 files changed, 15 insertions(+), 33 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
> index cdefafd456c70335..3d4da7e5270c8d4d 100644
> --- a/arch/x86/boot/compressed/head_64.S
> +++ b/arch/x86/boot/compressed/head_64.S
> @@ -430,24 +430,12 @@ SYM_CODE_START(startup_64)
> #endif
>
> /*
> - * paging_prepare() sets up the trampoline and checks if we need to
> - * enable 5-level paging.
> - *
> - * paging_prepare() returns a two-quadword structure which lands
> - * into RDX:RAX:
> - * - Address of the trampoline is returned in RAX.
> - * - Non zero RDX means trampoline needs to enable 5-level
> - * paging.
> - *
> + * set_paging_levels() updates the number of paging levels using a
> + * trampoline in 32-bit addressable memory if the current number does
> + * not match the desired number.
> */
> movq %r15, %rdi /* pass struct boot_params pointer */
> - call paging_prepare
> -
> - /* Pass the trampoline address and boolean flag as args #1 and #2 */
> - movq %rax, %rdi
> - movq %rdx, %rsi
> - leaq TRAMPOLINE_32BIT_CODE_OFFSET(%rax), %rax
> - call *%rax
> + call set_paging_levels
>
> /*
> * cleanup_trampoline() would restore trampoline memory.
> diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
> index d66639c961b8eeda..1d28ad95ea839531 100644
> --- a/arch/x86/boot/compressed/pgtable_64.c
> +++ b/arch/x86/boot/compressed/pgtable_64.c
> @@ -16,11 +16,6 @@ unsigned int __section(".data") pgdir_shift = 39;
> unsigned int __section(".data") ptrs_per_p4d = 1;
> #endif
>
> -struct paging_config {
> - unsigned long trampoline_start;
> - unsigned long l5_required;
> -};
> -
> /* Buffer to preserve trampoline memory */
> static char trampoline_save[TRAMPOLINE_32BIT_SIZE];
>
> @@ -106,10 +101,10 @@ static unsigned long find_trampoline_placement(void)
> return bios_start - TRAMPOLINE_32BIT_SIZE;
> }
>
> -struct paging_config paging_prepare(void *rmode)
> +asmlinkage void set_paging_levels(void *rmode)
Can you please change the refer to paging_prepare() in the comments above also?
