我Linux已经使用IOMMUfeature编译ON了dmesg日志，可以确保：
[root@dhb5 vm]# dmesg | grep -e DMAR -e IOMMU
[ 0.000000] ACPI: DMAR 000000007bfbb000 00368 (v01 HP 03010201 00000002 HPAG 00020000)
[ 0.000000] DMAR: IOMMU enabled
[ 0.512361] DMAR: Host address width 44
[ 0.516675] DMAR: DRHD base: 0x00000093ff8000 flags: 0x0
[ 0.522664] DMAR: IOMMU 0: reg_base_addr 93ff8000 ver 1:0 cap d2078c106f0466 ecap f020de
[ 0.531762] DMAR: DRHD base: 0x00000097ff8000 flags: 0x0
[ 0.537744] DMAR: IOMMU 1: reg_base_addr 97ff8000 ver 1:0 cap d2078c106f0466 ecap f020de
[ 0.546837] DMAR: DRHD base: 0x0000009bff8000 flags: 0x0
[ 0.552829] DMAR: IOMMU 2: reg_base_addr 9bff8000 ver 1:0 cap d2078c106f0466 ecap f020de
[ 0.561922] DMAR: DRHD base: 0x0000009fff8000 flags: 0x0
[ 0.567904] DMAR: IOMMU 3: reg_base_addr 9fff8000 ver 1:0 cap d2078c106f0466 ecap f020de
[ 0.576994] DMAR: RMRR base: 0x00000079911000 end: 0x00000079913fff
[ 0.584038] DMAR: RMRR base: 0x0000007990e000 end: 0x00000079910fff
[ 0.591079] DMAR: ATSR flags: 0x0
[ 0.594805] DMAR: ATSR flags: 0x0
[ 0.598530] DMAR: ATSR flags: 0x0
[ 0.602255] DMAR: ATSR flags: 0x0
[ 0.605982] DMAR: RHSA base: 0x00000093ff8000 proximity domain: 0x0
[ 0.613024] DMAR: RHSA base: 0x00000097ff8000 proximity domain: 0x1
[ 0.620067] DMAR: RHSA base: 0x0000009bff8000 proximity domain: 0x2
[ 0.627110] DMAR: RHSA base: 0x0000009fff8000 proximity domain: 0x3
[ 0.634163] DMAR-IR: IOAPIC id 13 under DRHD base 0x9fff8000 IOMMU 3
[ 0.641411] DMAR-IR: IOAPIC id 11 under DRHD base 0x9bff8000 IOMMU 2
[ 0.648647] DMAR-IR: IOAPIC id 12 under DRHD base 0x9bff8000 IOMMU 2
[ 0.655887] DMAR-IR: IOAPIC id 10 under DRHD base 0x97ff8000 IOMMU 1
[ 0.663126] DMAR-IR: IOAPIC id 8 under DRHD base 0x93ff8000 IOMMU 0
[ 0.670264] DMAR-IR: IOAPIC id 9 under DRHD base 0x93ff8000 IOMMU 0
[ 0.677404] DMAR-IR: HPET id 0 under DRHD base 0x93ff8000
[ 0.683483] DMAR-IR: Queued invalidation will be enabled to support x2apic and Intr-remapping.
[ 0.696950] DMAR-IR: Enabled IRQ remapping in x2apic mode
[ 5.505856] DMAR: dmar3: Using Queued invalidation
[ 5.511765] DMAR: dmar2: Using Queued invalidation
[ 5.517667] DMAR: dmar1: Using Queued invalidation
[ 5.523223] DMAR: dmar0: Using Queued invalidation
[ 5.528914] DMAR: Setting RMRR:
[ 5.532484] DMAR: Setting identity map for device 0000:20:1d.0 [0x7990e000 - 0x79910fff]
[ 5.541659] DMAR: Setting identity map for device 0000:00:1d.0 [0x79911000 - 0x79913fff]
[ 5.550776] DMAR: Prepare 0-16MiB unity mapping for LPC
[ 5.556672] DMAR: Setting identity map for device 0000:00:1f.0 [0x0 - 0xffffff]
[ 5.564908] DMAR: PCI-DMA: Intel(R) Virtualization Technology for Directed I/O
但是执行以下测试代码：
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <unistd.h>
#include <linux/kvm.h>
#define KVM_FILE "/dev/kvm"
int main(void)
{
int dev;
int ret;
dev = open(KVM_FILE,O_RDWR|O_NDELAY);
ret = ioctl(dev,KVM_CHECK_EXTENSION,KVM_CAP_IOMMU);
if(ret != 0)
printf("----KVM supports IOMMU (i.e. Intel VT-d or AMD IOMMU).----\n");
else
printf("----KVM doesn't support IOMMU (i.e. Intel VT-d or AMD IOMMU).----\n");
return 0;
}
输出为：
----KVM doesn't support IOMMU (i.e. Intel VT-d or AMD IOMMU).----
我有点困惑，因为从dmesg日志中，内核已经报告了它支持IOMMU，为什么ioctl命令假定kernel不支持IOMMU？
已找到根本原因，需要配置KVM_DEVICE_ASSIGNMENT选项以构建内核。因为在kvm_vm_ioctl_check_extension功能上：
#ifdef CONFIG_KVM_DEVICE_ASSIGNMENT
case KVM_CAP_IOMMU:
r = iommu_present(&pci_bus_type);
break;
#endif
没有此选项，函数将0直接返回。
请参阅此讨论。
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我来说两句