Commit 269e2358 authored by Paolo Bonzini's avatar Paolo Bonzini
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linuxboot: fix loading old kernels 



Old kernels that used high memory only allowed the initrd to be in the
first 896MB of memory.  If you load the initrd above, they complain
that "initrd extends beyond end of memory".

In order to fix this, while not breaking machines with small amounts
of memory fixed by cdebec5e (linuxboot: compute initrd loading address,
2014-10-06), we need to distinguish two cases.  If pc.c placed the
initrd at end of memory, use the new algorithm based on the e801
memory map.  If instead pc.c placed the initrd at the maximum address
specified by the bzImage, leave it there.

The only interesting part is that the low-memory info block is now
loaded very early, in real mode, and thus the 32-bit address has
to be converted into a real mode segment.  The initrd address is
also patched in the info block before entering real mode, it is
simpler that way.

This fixes booting the RHEL4.8 32-bit installation image with 1GB
of RAM.

Cc: qemu-stable@nongnu.org
Cc: mst@redhat.com
Cc: jsnow@redhat.com
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 575a6f40

pc-bios/linuxboot.bin

(1 KiB)

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pc-bios/optionrom/linuxboot.S

+27 −10
Original line number Diff line number Diff line
@@ -76,7 +76,31 @@ boot_kernel: 




copy_kernel:

	/* Compute initrd address */

	/* Read info block in low memory (0x10000 or 0x90000) */

	read_fw		FW_CFG_SETUP_ADDR

	shr		$4, %eax

	mov		%eax, %es

	xor		%edi, %edi

	read_fw_blob_addr32_edi(FW_CFG_SETUP)



	cmpw            $0x203, %es:0x206      // if protocol >= 0x203

	jae             1f                     // have initrd_max

	movl            $0x37ffffff, %es:0x22c // else assume 0x37ffffff

1:



	/* Check if using kernel-specified initrd address */

	read_fw		FW_CFG_INITRD_ADDR

	mov		%eax, %edi             // (load_kernel wants it in %edi)

	read_fw		FW_CFG_INITRD_SIZE     // find end of initrd

	add		%edi, %eax

	xor		%es:0x22c, %eax        // if it matches es:0x22c

	and		$-4096, %eax           // (apart from padding for page)

	jz		load_kernel            // then initrd is not at top

					       // of memory



	/* pc.c placed the initrd at end of memory.  Compute a better

	 * initrd address based on e801 data.

	 */

	mov		$0xe801, %ax

	xor		%cx, %cx

	xor		%dx, %dx
@@ -107,7 +131,9 @@ copy_kernel: 
	read_fw         FW_CFG_INITRD_SIZE

	subl            %eax, %edi

	andl            $-4096, %edi          /* EDI = start of initrd */

	movl		%edi, %es:0x218       /* put it in the header */



load_kernel:

	/* We need to load the kernel into memory we can't access in 16 bit

	   mode, so let's get into 32 bit mode, write the kernel and jump

	   back again. */
@@ -139,19 +165,10 @@ copy_kernel: 
	/* We're now running in 16-bit CS, but 32-bit ES! */



	/* Load kernel and initrd */

	pushl		%edi

	read_fw_blob_addr32_edi(FW_CFG_INITRD)

	read_fw_blob_addr32(FW_CFG_KERNEL)

	read_fw_blob_addr32(FW_CFG_CMDLINE)



	read_fw		FW_CFG_SETUP_ADDR

	mov		%eax, %edi

	mov		%eax, %ebx

	read_fw_blob_addr32_edi(FW_CFG_SETUP)



	/* Update the header with the initrd address we chose above */

	popl		%es:0x218(%ebx)



	/* And now jump into Linux! */

	mov		$0, %eax

	mov		%eax, %cr0