接前一篇文章:
上一回讲到了pci_edu_realize函数中的pci_register_bar函数,本回对于其进行详细解析。
再次贴出pci_register_bar函数源码,在hw/pci/pci.c中,代码如下:
void pci_register_bar(PCIDevice *pci_dev, int region_num,
uint8_t type, MemoryRegion *memory)
{
PCIIORegion *r;
uint32_t addr; /* offset in pci config space */
uint64_t wmask;
pcibus_t size = memory_region_size(memory);
uint8_t hdr_type;
assert(!pci_is_vf(pci_dev)); /* VFs must use pcie_sriov_vf_register_bar */
assert(region_num >= 0);
assert(region_num < PCI_NUM_REGIONS);
assert(is_power_of_2(size));
/* A PCI bridge device (with Type 1 header) may only have at most 2 BARs */
hdr_type =
pci_dev->config[PCI_HEADER_TYPE] & ~PCI_HEADER_TYPE_MULTI_FUNCTION;
assert(hdr_type != PCI_HEADER_TYPE_BRIDGE || region_num < 2);
r = &pci_dev->io_regions[region_num];
r->addr = PCI_BAR_UNMAPPED;
r->size = size;
r->type = type;
r->memory = memory;
r->address_space = type & PCI_BASE_ADDRESS_SPACE_IO
? pci_get_bus(pci_dev)->address_space_io
: pci_get_bus(pci_dev)->address_space_mem;
wmask = ~(size - 1);
if (region_num == PCI_ROM_SLOT) {
/* ROM enable bit is writable */
wmask |= PCI_ROM_ADDRESS_ENABLE;
}
addr = pci_bar(pci_dev, region_num);
pci_set_long(pci_dev->config + addr, type);
if (!(r->type & PCI_BASE_ADDRESS_SPACE_IO) &&
r->type & PCI_BASE_ADDRESS_MEM_TYPE_64) {
pci_set_quad(pci_dev->wmask + addr, wmask);
pci_set_quad(pci_dev->cmask + addr, ~0ULL);
} else {
pci_set_long(pci_dev->wmask + addr, wmask & 0xffffffff);
pci_set_long(pci_dev->cmask + addr, 0xffffffff);
}
}
(1)首先根据region_num找到PCIDevice->io_regions数组中对应的项。PCI设备的MMIO存放在PCIIORegion结构体中,结构体中保存了MMIO的地址、大小、类型等信息。
代码片段如下:
r = &pci_dev->io_regions[region_num];
(2)得到region_num表示的PCIIORegion之后,进行一些初始化设置。
r->addr = PCI_BAR_UNMAPPED;
r->size = size;
r->type = type;
r->memory = memory;
r->address_space = type & PCI_BASE_ADDRESS_SPACE_IO
? pci_get_bus(pci_dev)->address_space_io
: pci_get_bus(pci_dev)->address_space_mem;
(3)然后将该region的type写到相应PCI配置空间对应BAR的地址处。代码片段如下:
r->address_space = type & PCI_BASE_ADDRESS_SPACE_IO
? pci_get_bus(pci_dev)->address_space_io
: pci_get_bus(pci_dev)->address_space_mem;
(4)最后设置PCI Device中wmask和cmask的值。代码片段如下:
wmask = ~(size - 1);
if (region_num == PCI_ROM_SLOT) {
/* ROM enable bit is writable */
wmask |= PCI_ROM_ADDRESS_ENABLE;
}
addr = pci_bar(pci_dev, region_num);
pci_set_long(pci_dev->config + addr, type);
if (!(r->type & PCI_BASE_ADDRESS_SPACE_IO) &&
r->type & PCI_BASE_ADDRESS_MEM_TYPE_64) {
pci_set_quad(pci_dev->wmask + addr, wmask);
pci_set_quad(pci_dev->cmask + addr, ~0ULL);
} else {
pci_set_long(pci_dev->wmask + addr, wmask & 0xffffffff);
pci_set_long(pci_dev->cmask + addr, 0xffffffff);
}
操作系统与PCI设备交互的主要方式是PIO和MMIO。MMIO虽然是一段内存,但是其没有EPT映射,在虚拟机访问设备的MMIO时,会产生VM Exit;KVM识别此MMIO访问并且将该访问分派到应用层QEMU中;QEMU根据内存虚拟化的步骤进行分派,找到设备注册的MMIO读写回调函数;设备的MMIO读写回调函数根据设备的功能进行模拟,完成模拟之后可能会发送中断到虚拟机中,从而完成一些MMIO访问。文章来源:https://www.toymoban.com/news/detail-792623.html
下一回将开始解析edu设备的MMIO读写函数。文章来源地址https://www.toymoban.com/news/detail-792623.html
到了这里,关于QEMU源码全解析 —— PCI设备模拟(6)的文章就介绍完了。如果您还想了解更多内容,请在右上角搜索TOY模板网以前的文章或继续浏览下面的相关文章,希望大家以后多多支持TOY模板网!