Re: [PATCH] arm64/efi: prefer AllocatePages() over efi_low_alloc() for vmlinux

[Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>]

Hi Ard,

On Fri, Jul 24, 2015 at 10:41:53AM +0100, Ard Biesheuvel wrote:
> When allocating memory for the kernel image, try the AllocatePages()
> boot service to obtain memory at the preferred offset of
> 'dram_base + TEXT_OFFSET', and only revert to efi_low_alloc() if that
> fails. This is the only way to allocate at the base of DRAM if DRAM
> starts at 0x0, since efi_low_alloc() refuses to allocate at 0x0.
>
> Tested-by: Haojian Zhuang <haojian.zhuang-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> ---
>  arch/arm64/kernel/efi-stub.c | 47 ++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 39 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm64/kernel/efi-stub.c b/arch/arm64/kernel/efi-stub.c
> index f5374065ad53..c8df74d14368 100644
> --- a/arch/arm64/kernel/efi-stub.c
> +++ b/arch/arm64/kernel/efi-stub.c
> @@ -13,7 +13,7 @@
>  #include <asm/efi.h>
>  #include <asm/sections.h>
>  
> -efi_status_t __init handle_kernel_image(efi_system_table_t *sys_table,
> +efi_status_t __init handle_kernel_image(efi_system_table_t *sys_table_arg,

Any reason for the _arg addition?

>  					unsigned long *image_addr,
>  					unsigned long *image_size,
>  					unsigned long *reserve_addr,
> @@ -23,21 +23,52 @@ efi_status_t __init handle_kernel_image(efi_system_table_t *sys_table,
>  {
>  	efi_status_t status;
>  	unsigned long kernel_size, kernel_memsize = 0;
> +	unsigned long nr_pages;
>  
>  	/* Relocate the image, if required. */
>  	kernel_size = _edata - _text;
>  	if (*image_addr != (dram_base + TEXT_OFFSET)) {
>  		kernel_memsize = kernel_size + (_end - _edata);
> -		status = efi_low_alloc(sys_table, kernel_memsize + TEXT_OFFSET,
> -				       SZ_2M, reserve_addr);
> +
> +		//
> +		// First, try a straight allocation at the preferred offset.
> +		// This will work around the issue where, if dram_base == 0x0,
> +		// efi_low_alloc() refuses to allocate at 0x0 (to prevent the
> +		// address of the allocation to be mistaken for a FAIL return
> +		// value or a NULL pointer). It will also ensure that, on
> +		// platforms where the [dram_base, dram_base + TEXT_OFFSET)
> +		// interval is partially occupied by the firmware (like on APM
> +		// Mustang), we can still place the kernel at the address
> +		// 'dram_base + TEXT_OFFSET'.
> +		//

/*
 * Nit: please use the standard comment style
 */

> +		*reserve_addr = dram_base + TEXT_OFFSET;
> +		nr_pages = round_up(kernel_memsize, EFI_ALLOC_ALIGN) /
> +			   EFI_PAGE_SIZE;
> +		status = efi_call_early(allocate_pages, EFI_ALLOCATE_ADDRESS,
> +					EFI_LOADER_DATA, nr_pages,
> +					(efi_physical_addr_t *)reserve_addr);
> +		if (status == EFI_SUCCESS) {
> +			memcpy((void *)*reserve_addr, (void *)*image_addr,
> +			       kernel_size);
> +			*image_addr = *reserve_addr;
> +			*reserve_size = kernel_memsize;
> +		} else {
> +			status = efi_low_alloc(sys_table_arg,
> +					       kernel_memsize + TEXT_OFFSET,
> +					       SZ_2M, reserve_addr);
> +
> +			if (status == EFI_SUCCESS) {
> +				memcpy((void *)*reserve_addr + TEXT_OFFSET,
> +				       (void *)*image_addr,
> +				       kernel_size);
> +				*image_addr = *reserve_addr + TEXT_OFFSET;
> +				*reserve_size = kernel_memsize + TEXT_OFFSET;
> +			}
> +		}
>  		if (status != EFI_SUCCESS) {
> -			pr_efi_err(sys_table, "Failed to relocate kernel\n");
> +			pr_efi_err(sys_table_arg, "Failed to relocate kernel\n");
>  			return status;
>  		}
> -		memcpy((void *)*reserve_addr + TEXT_OFFSET, (void *)*image_addr,
> -		       kernel_size);

Could we have a new_image_addr assigned in each case, and keep the
common memcpy here, followed by assignment to *image_addr? That would
save a couple of lines and guarantee the two cases stay in sync.

Otherwise this looks good to me.

Thanks,
Mark.