Re: [PATCH v2] arm64/efi: prefer AllocatePages() over efi_low_alloc() for vmlinux

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

On Fri, Jul 24, 2015 at 12:38:27PM +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>

Reviewed-by: Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>

Mark.

> ---
> v2:
> - reshuffle code flow to make it more logical, and have only a single
>   memcpy() invocation at the end of the function
> ---
>  arch/arm64/kernel/efi-stub.c | 41 ++++++++++++++++++++++++++++++++---------
>  1 file changed, 32 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm64/kernel/efi-stub.c b/arch/arm64/kernel/efi-stub.c
> index f5374065ad53..816120ece6bc 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,
>  					unsigned long *image_addr,
>  					unsigned long *image_size,
>  					unsigned long *reserve_addr,
> @@ -23,21 +23,44 @@ 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;
> +	void *old_image_addr = (void *)*image_addr;
>  
>  	/* 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'.
> +		 */
> +		*image_addr = *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) {
> -			pr_efi_err(sys_table, "Failed to relocate kernel\n");
> -			return status;
> +			kernel_memsize += TEXT_OFFSET;
> +			status = efi_low_alloc(sys_table_arg, kernel_memsize,
> +					       SZ_2M, reserve_addr);
> +
> +			if (status != EFI_SUCCESS) {
> +				pr_efi_err(sys_table_arg, "Failed to relocate kernel\n");
> +				return status;
> +			}
> +			*image_addr = *reserve_addr + TEXT_OFFSET;
>  		}
> -		memcpy((void *)*reserve_addr + TEXT_OFFSET, (void *)*image_addr,
> -		       kernel_size);
> -		*image_addr = *reserve_addr + TEXT_OFFSET;
> -		*reserve_size = kernel_memsize + TEXT_OFFSET;
> +		memcpy((void *)*image_addr, old_image_addr, kernel_size);
> +		*reserve_size = kernel_memsize;
>  	}
>  
>  
> -- 
> 1.9.1
>