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optionrom: add a DMA-enabled multiboot ROM

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Add a new option rom for the multiboot loader, using DMA transfers to copy
data instead of "rep insb".

This significantly lowers QEMU's startup latency by a factor of about 40,
for example, going from 30sec to 0.8sec when loading modules of 120MB
in size.

Signed-off-by: Marcus Hähnel <marcus.haehnel@kernkonzept.com>
Signed-off-by: Adam Lackorzynski <adam@l4re.org>
[Modified to keep the non-DMA code depending on #ifdef USE_FW_CFG_DMA;
 do not write below stack. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Marcus Hähnel 2021-10-20 14:55:04 +02:00 • committed by Paolo Bonzini
parent f014c97459
commit 48972f8cad
6 changed files with 72 additions and 5 deletions
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66
pc-bios/optionrom/optionrom.h
View file

@ -37,6 +37,17 @@
#define BIOS_CFG_IOPORT_CFG 0x510
#define BIOS_CFG_IOPORT_DATA 0x511
#define FW_CFG_DMA_CTL_ERROR 0x01
#define FW_CFG_DMA_CTL_READ 0x02
#define FW_CFG_DMA_CTL_SKIP 0x04
#define FW_CFG_DMA_CTL_SELECT 0x08
#define FW_CFG_DMA_CTL_WRITE 0x10
#define FW_CFG_DMA_SIGNATURE 0x51454d5520434647ULL /* "QEMU CFG" */
#define BIOS_CFG_DMA_ADDR_HIGH 0x514
#define BIOS_CFG_DMA_ADDR_LOW 0x518
/* Break the translation block flow so -d cpu shows us values */
#define DEBUG_HERE \
jmp 1f; \
@ -62,6 +73,61 @@
bswap %eax
.endm
/*
* Read data from the fw_cfg device using DMA.
* Clobbers: %edx, %eax, ADDR, SIZE, memory[%esp-16] to memory[%esp]
*/
.macro read_fw_dma VAR, SIZE, ADDR
/* Address */
bswapl \ADDR
pushl \ADDR
/* We only support 32 bit target addresses */
xorl %eax, %eax
pushl %eax
mov $BIOS_CFG_DMA_ADDR_HIGH, %dx
outl %eax, (%dx)
/* Size */
bswapl \SIZE
pushl \SIZE
/* Control */
movl $(\VAR << 16) | (FW_CFG_DMA_CTL_READ | FW_CFG_DMA_CTL_SELECT), %eax
bswapl %eax
pushl %eax
movl %esp, %eax /* Address of the struct we generated */
bswapl %eax
mov $BIOS_CFG_DMA_ADDR_LOW, %dx
outl %eax, (%dx) /* Initiate DMA */
1: mov (%esp), %eax /* Wait for completion */
bswapl %eax
testl $~FW_CFG_DMA_CTL_ERROR, %eax
jnz 1b
addl $16, %esp
.endm
/*
* Read a blob from the fw_cfg device using DMA
* Requires _ADDR, _SIZE and _DATA values for the parameter.
*
* Clobbers: %eax, %edx, %es, %ecx, %edi and adresses %esp-20 to %esp
*/
#ifdef USE_FW_CFG_DMA
#define read_fw_blob_dma(var) \
read_fw var ## _SIZE; \
mov %eax, %ecx; \
read_fw var ## _ADDR; \
mov %eax, %edi ;\
read_fw_dma var ## _DATA, %ecx, %edi
#else
#define read_fw_blob_dma(var) read_fw_blob(var)
#endif
#define read_fw_blob_pre(var) \
read_fw var ## _SIZE; \
mov %eax, %ecx; \