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Re: [Qemu-devel] [PATCH] linuxboot: compute initrd loading address
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH] linuxboot: compute initrd loading address |
Date: |
Tue, 7 Oct 2014 11:46:51 +0300 |
On Mon, Oct 06, 2014 at 04:49:57PM +0200, Paolo Bonzini wrote:
> Even though hw/i386/pc.c tries to compute a valid loading address for the
> initrd, close to the top of RAM, this does not take into account other
> data that is malloced into that memory by SeaBIOS.
>
> Luckily we can easily look at the memory map to find out how much memory is
> used up there. This patch places the initrd in the first four gigabytes,
> below the first hole (as returned by INT 15h, AX=e801h).
>
> Without this patch:
> [ 0.000000] init_memory_mapping: [mem 0x07000000-0x07fdffff]
> [ 0.000000] RAMDISK: [mem 0x0710a000-0x07fd7fff]
>
> With this patch:
> [ 0.000000] init_memory_mapping: [mem 0x07000000-0x07fdffff]
> [ 0.000000] RAMDISK: [mem 0x07112000-0x07fdffff]
>
> So linuxboot is able to use the 64k that were added as padding for
> QEMU <= 2.1.
>
> Signed-off-by: Paolo Bonzini <address@hidden>
Acked-by: Michael S. Tsirkin <address@hidden>
OK, and we need something similar for multiboot.S?
Also - can we drop FW_CFG_INITRD_ADDR and the patching
in load_linux now (unless running a compat machine type)?
> ---
> pc-bios/linuxboot.bin | Bin 1024 -> 1024 bytes
> pc-bios/optionrom/linuxboot.S | 47
> ++++++++++++++++++++++++++++++++++++++----
> pc-bios/optionrom/optionrom.h | 21 ++++++++++++++++---
> 3 files changed, 61 insertions(+), 7 deletions(-)
>
> diff --git a/pc-bios/linuxboot.bin b/pc-bios/linuxboot.bin
> index
> e7c36694f997c3c34f7f4af3c2923bd2ef6094e7..130103fb739228a6869aaf1b174b9d20c13378fc
> 100644
> GIT binary patch
> delta 168
> zcmZqRXyBNj#e9V6<address@hidden|bXJt}WGM&drBas8gPpg4G+*OE29`Ab?LX5F
> zKIeMP(|Cx15y<-m<Oxh}WRz3ZJf7D0oZ-X&|7o31)0*E19C!O5&XCq~0;uRf+QA1b
> zX{>7|eo$aa3kRw;nk>i|IC(Q;0c%?4;address@hidden;0)C|f
> SJtz7Oyqvi?nJI*kF&F^X7ev$m
>
> delta 107
> address@hidden|`VlnOD22!$<yBUQi
> zzh^99+93|&DjwV+!H~8~fR%ya{VqY)Kk1)y(snQa0l(6Lo)disUOwEsnkj^F@&_gl
> G#(w~}wj;0r
>
> diff --git a/pc-bios/optionrom/linuxboot.S b/pc-bios/optionrom/linuxboot.S
> index 748c831..5bc0af0 100644
> --- a/pc-bios/optionrom/linuxboot.S
> +++ b/pc-bios/optionrom/linuxboot.S
> @@ -76,14 +76,45 @@ boot_kernel:
>
>
> copy_kernel:
> + /* Compute initrd address */
> + mov $0xe801, %ax
> + xor %cx, %cx
> + xor %dx, %dx
> + int $0x15
> +
> + /* Output could be in AX/BX or CX/DX */
> + or %cx, %cx
> + jnz 1f
> + or %dx, %dx
> + jnz 1f
> + mov %ax, %cx
> + mov %bx, %dx
> +1:
> +
> + or %dx, %dx
> + jnz 2f
> + addw $1024, %cx /* add 1 MB */
> + movzwl %cx, %edi
> + shll $10, %edi /* convert to bytes */
> + jmp 3f
> +
> +2:
> + addw $16777216 >> 16, %dx /* add 16 MB */
> + movzwl %dx, %edi
> + shll $16, %edi /* convert to bytes */
> +
> +3:
> + read_fw FW_CFG_INITRD_SIZE
> + subl %eax, %edi
> + andl $-4096, %edi /* EDI = start of initrd */
>
> /* 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. */
>
> /* Reserve space on the stack for our GDT descriptor. */
> - mov %esp, %ebp
> - sub $16, %esp
> + mov %esp, %ebp
> + sub $16, %esp
>
> /* Now create the GDT descriptor */
> movw $((3 * 8) - 1), -16(%bp)
> @@ -108,10 +139,18 @@ 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_INITRD)
> read_fw_blob_addr32(FW_CFG_CMDLINE)
> - read_fw_blob_addr32(FW_CFG_SETUP)
> +
> + 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
> diff --git a/pc-bios/optionrom/optionrom.h b/pc-bios/optionrom/optionrom.h
> index ce43608..f1a9021 100644
> --- a/pc-bios/optionrom/optionrom.h
> +++ b/pc-bios/optionrom/optionrom.h
> @@ -51,8 +51,6 @@
> .endm
>
> #define read_fw_blob_pre(var) \
> - read_fw var ## _ADDR; \
> - mov %eax, %edi; \
> read_fw var ## _SIZE; \
> mov %eax, %ecx; \
> mov $var ## _DATA, %ax; \
> @@ -68,6 +66,8 @@
> * Clobbers: %eax, %edx, %es, %ecx, %edi
> */
> #define read_fw_blob(var) \
> + read_fw var ## _ADDR; \
> + mov %eax, %edi; \
> read_fw_blob_pre(var); \
> /* old as(1) doesn't like this insn so emit the bytes instead: \
> rep insb (%dx), %es:(%edi); \
> @@ -80,7 +80,22 @@
> *
> * Clobbers: %eax, %edx, %es, %ecx, %edi
> */
> -#define read_fw_blob_addr32(var) \
> +#define read_fw_blob_addr32(var) \
> + read_fw var ## _ADDR; \
> + mov %eax, %edi; \
> + read_fw_blob_pre(var); \
> + /* old as(1) doesn't like this insn so emit the bytes instead: \
> + addr32 rep insb (%dx), %es:(%edi); \
> + */ \
> + .dc.b 0x67,0xf3,0x6c
> +
> +/*
> + * Read a blob from the fw_cfg device in forced addr32 mode, address is in
> %edi.
> + * Requires _SIZE and _DATA values for the parameter.
> + *
> + * Clobbers: %eax, %edx, %edi, %es, %ecx
> + */
> +#define read_fw_blob_addr32_edi(var) \
> read_fw_blob_pre(var); \
> /* old as(1) doesn't like this insn so emit the bytes instead: \
> addr32 rep insb (%dx), %es:(%edi); \
> --
> 2.1.0