diff mbox

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

Message ID 1437737907-10477-1-git-send-email-ard.biesheuvel@linaro.org
State Accepted
Commit e38457c361b30c5a2379cc767877c3e5c2505dc6
Headers show

Commit Message

Ard Biesheuvel July 24, 2015, 11:38 a.m. UTC 
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@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
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(-)

Comments

Ard Biesheuvel July 28, 2015, 9:24 p.m. UTC | #1 
On 28 July 2015 at 23:17, Matt Fleming <matt@codeblueprint.co.uk> wrote:
> On Fri, 24 Jul, at 01:38:27PM, 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@linaro.org>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> ---
>> 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(-)
>
> Would it be easier if we allow efi_low_alloc() to return 0x0 for some
> uses? If you don't need the preference for low allocations, probably
> not, but I don't want to see us working around limitations in
> efi_low_alloc() instead of just fixing it.
>

This workaround fixes another issue as well: the arm64 kernel needs to
be loaded 512 KB above a 2MB aligned boundary, and using
efi_low_alloc() as we do loses (2 MB - 512 KB) at the bottom if part
of that 512 KB is occupied, since efi_low_alloc() is not aware of the
fact that the first 512 KB will remain unused.

What would be most helpful is if efi_low_alloc() could take an offset
param in addition to the alignment, i.e., alignment == 2MB and offset
== 512 KB. The offset would default to 0, reverting to the original
behavior.

If you'd be ok with such a change, I can propose it instead, and wire
it up into this function.
diff mbox

Patch

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;
 	}