简单浏览下 svm.c 的代码

一些硬件机制，简单了解一下

efer

efer_trap : https://en.wikipedia.org/wiki/Control_register

功能定义在: arch/x86/include/asm/msr-index.h

例如:

/* EFER bits: */
#define _EFER_NX		11 /* No execute enable */

让页面不可执行。

others

svm_init_osvw
- AMD 手册 volume 2 : Appendix E OS-Visible Workarounds
```
#define X86_FEATURE_OSVW		( 6*32+ 9) /* OS Visible Workaround */
```
svm_enable_lbrv : ( last branch records) : https://lwn.net/Articles/680985/
grow_ple_window : https://patchwork.kernel.org/project/kvm/patch/1408637291-18533-5-git-send-email-rkrcmar@redhat.com/
- https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/6.2_release_notes/virtualization
- Pause Loop Exiting
svm_set_vnmi_pending : vnmi 有什么特别的吗?
ud_interception
svm_cache_reg : 中间的 pdptr 不太知道是什么意思?

这些 interception 似乎是

static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = {
	[SVM_EXIT_READ_CR0]			= cr_interception,
	[SVM_EXIT_READ_CR3]			= cr_interception,
	[SVM_EXIT_READ_CR4]			= cr_interception,
	[SVM_EXIT_READ_CR8]			= cr_interception,
	[SVM_EXIT_CR0_SEL_WRITE]		= cr_interception,
	[SVM_EXIT_WRITE_CR0]			= cr_interception,
	[SVM_EXIT_WRITE_CR3]			= cr_interception,
	[SVM_EXIT_WRITE_CR4]			= cr_interception,
	[SVM_EXIT_WRITE_CR8]			= cr8_write_interception,
	[SVM_EXIT_READ_DR0]			= dr_interception,
	[SVM_EXIT_READ_DR1]			= dr_interception,
	[SVM_EXIT_READ_DR2]			= dr_interception,
	[SVM_EXIT_READ_DR3]			= dr_interception,
	[SVM_EXIT_READ_DR4]			= dr_interception,
	[SVM_EXIT_READ_DR5]			= dr_interception,
	[SVM_EXIT_READ_DR6]			= dr_interception,
	[SVM_EXIT_READ_DR7]			= dr_interception,
	[SVM_EXIT_WRITE_DR0]			= dr_interception,
	[SVM_EXIT_WRITE_DR1]			= dr_interception,
	[SVM_EXIT_WRITE_DR2]			= dr_interception,
	[SVM_EXIT_WRITE_DR3]			= dr_interception,
	[SVM_EXIT_WRITE_DR4]			= dr_interception,
	[SVM_EXIT_WRITE_DR5]			= dr_interception,
	[SVM_EXIT_WRITE_DR6]			= dr_interception,
	[SVM_EXIT_WRITE_DR7]			= dr_interception,
	[SVM_EXIT_EXCP_BASE + DB_VECTOR]	= db_interception,
	[SVM_EXIT_EXCP_BASE + BP_VECTOR]	= bp_interception,
	[SVM_EXIT_EXCP_BASE + UD_VECTOR]	= ud_interception,
	[SVM_EXIT_EXCP_BASE + PF_VECTOR]	= pf_interception,
	[SVM_EXIT_EXCP_BASE + MC_VECTOR]	= mc_interception,
	[SVM_EXIT_EXCP_BASE + AC_VECTOR]	= ac_interception,
	[SVM_EXIT_EXCP_BASE + GP_VECTOR]	= gp_interception,
	[SVM_EXIT_INTR]				= intr_interception,
	[SVM_EXIT_NMI]				= nmi_interception,
	[SVM_EXIT_SMI]				= smi_interception,
  // ...
}

如果 disable npt ，代码的执行流程是什么?

找一些 reference :

svm_set_efer : 为什么 shadow page 需要支持 EFER_NX
svm_recalc_instruction_intercepts : shadow page 需要 intercept INVPCID 来实现 shadow page flush

init_vmcb

  if (npt_enabled) {
      /* Setup VMCB for Nested Paging */
      control->nested_ctl |= SVM_NESTED_CTL_NP_ENABLE;
      svm_clr_intercept(svm, INTERCEPT_INVLPG);
      clr_exception_intercept(svm, PF_VECTOR);
      svm_clr_intercept(svm, INTERCEPT_CR3_READ);
      svm_clr_intercept(svm, INTERCEPT_CR3_WRITE);
      save->g_pat = vcpu->arch.pat;
      save->cr3 = 0;
  }

svm_set_cr0
svm_set_cr4
svm_handle_exit : 更新 cr3 有关
svm_load_mmu_pgd
svm_set_cpu_caps

看来，核心的流程都是在 mmu 上，其实 svm 没有很多的调整。

apic page !

static void *svm_alloc_apic_backing_page(struct kvm_vcpu *vcpu)
{
	struct page *page = snp_safe_alloc_page(vcpu);

	if (!page)
		return NULL;

	return page_address(page);
}

分析热迁移

static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = {
	[SVM_EXIT_READ_CR0]			= cr_interception,
	[SVM_EXIT_READ_CR3]			= cr_interception,
	[SVM_EXIT_READ_CR4]			= cr_interception,
	[SVM_EXIT_READ_CR8]			= cr_interception,
	[SVM_EXIT_CR0_SEL_WRITE]		= cr_interception,
	[SVM_EXIT_WRITE_CR0]			= cr_interception,
	[SVM_EXIT_WRITE_CR3]			= cr_interception,
	[SVM_EXIT_WRITE_CR4]			= cr_interception,
	[SVM_EXIT_WRITE_CR8]			= cr8_write_interception,
	[SVM_EXIT_READ_DR0]			= dr_interception,
	[SVM_EXIT_READ_DR1]			= dr_interception,
	[SVM_EXIT_READ_DR2]			= dr_interception,
	[SVM_EXIT_READ_DR3]			= dr_interception,
	[SVM_EXIT_READ_DR4]			= dr_interception,
	[SVM_EXIT_READ_DR5]			= dr_interception,
	[SVM_EXIT_READ_DR6]			= dr_interception,
	[SVM_EXIT_READ_DR7]			= dr_interception,
	[SVM_EXIT_WRITE_DR0]			= dr_interception,
	[SVM_EXIT_WRITE_DR1]			= dr_interception,
	[SVM_EXIT_WRITE_DR2]			= dr_interception,
	[SVM_EXIT_WRITE_DR3]			= dr_interception,
	[SVM_EXIT_WRITE_DR4]			= dr_interception,
	[SVM_EXIT_WRITE_DR5]			= dr_interception,
	[SVM_EXIT_WRITE_DR6]			= dr_interception,
	[SVM_EXIT_WRITE_DR7]			= dr_interception,
	[SVM_EXIT_EXCP_BASE + DB_VECTOR]	= db_interception,
	[SVM_EXIT_EXCP_BASE + BP_VECTOR]	= bp_interception,
	[SVM_EXIT_EXCP_BASE + UD_VECTOR]	= ud_interception,
	[SVM_EXIT_EXCP_BASE + PF_VECTOR]	= pf_interception,
	[SVM_EXIT_EXCP_BASE + MC_VECTOR]	= mc_interception,
	[SVM_EXIT_EXCP_BASE + AC_VECTOR]	= ac_interception,
	[SVM_EXIT_EXCP_BASE + GP_VECTOR]	= gp_interception,
	[SVM_EXIT_INTR]				= intr_interception,
	[SVM_EXIT_NMI]				= nmi_interception,
	[SVM_EXIT_SMI]				= smi_interception,
	[SVM_EXIT_VINTR]			= interrupt_window_interception,
	[SVM_EXIT_RDPMC]			= kvm_emulate_rdpmc,
	[SVM_EXIT_CPUID]			= kvm_emulate_cpuid,
	[SVM_EXIT_IRET]                         = iret_interception,
	[SVM_EXIT_INVD]                         = kvm_emulate_invd,
	[SVM_EXIT_PAUSE]			= pause_interception,
	[SVM_EXIT_HLT]				= kvm_emulate_halt,
	[SVM_EXIT_INVLPG]			= invlpg_interception,
	[SVM_EXIT_INVLPGA]			= invlpga_interception,
	[SVM_EXIT_IOIO]				= io_interception,
	[SVM_EXIT_MSR]				= msr_interception,
	[SVM_EXIT_TASK_SWITCH]			= task_switch_interception,
	[SVM_EXIT_SHUTDOWN]			= shutdown_interception,
	[SVM_EXIT_VMRUN]			= vmrun_interception,
	[SVM_EXIT_VMMCALL]			= kvm_emulate_hypercall,
	[SVM_EXIT_VMLOAD]			= vmload_interception,
	[SVM_EXIT_VMSAVE]			= vmsave_interception,
	[SVM_EXIT_STGI]				= stgi_interception,
	[SVM_EXIT_CLGI]				= clgi_interception,
	[SVM_EXIT_SKINIT]			= skinit_interception,
	[SVM_EXIT_RDTSCP]			= kvm_handle_invalid_op,
	[SVM_EXIT_WBINVD]                       = kvm_emulate_wbinvd,
	[SVM_EXIT_MONITOR]			= kvm_emulate_monitor,
	[SVM_EXIT_MWAIT]			= kvm_emulate_mwait,
	[SVM_EXIT_XSETBV]			= kvm_emulate_xsetbv,
	[SVM_EXIT_RDPRU]			= kvm_handle_invalid_op,
	[SVM_EXIT_EFER_WRITE_TRAP]		= efer_trap,
	[SVM_EXIT_CR0_WRITE_TRAP]		= cr_trap,
	[SVM_EXIT_CR4_WRITE_TRAP]		= cr_trap,
	[SVM_EXIT_CR8_WRITE_TRAP]		= cr_trap,
	[SVM_EXIT_INVPCID]                      = invpcid_interception,
	[SVM_EXIT_NPF]				= npf_interception,
	[SVM_EXIT_RSM]                          = rsm_interception,
	[SVM_EXIT_AVIC_INCOMPLETE_IPI]		= avic_incomplete_ipi_interception,
	[SVM_EXIT_AVIC_UNACCELERATED_ACCESS]	= avic_unaccelerated_access_interception,
	[SVM_EXIT_VMGEXIT]			= sev_handle_vmgexit,
};

kvm_emulate_mwait vs kvm_emulate_halt 到底使用哪一个

@[
    kvm_emulate_halt+5
    kvm_arch_vcpu_ioctl_run+1718
    kvm_vcpu_ioctl+587
    __x64_sys_ioctl+148
    do_syscall_64+197
    entry_SYSCALL_64_after_hwframe+111
]: 7231

kvm_emulate_monitor 和 kvm_emulate_mwait 不是默认支持的指令，会出发警告的！

kvm_emulate_wbinvd

使用

sudo bpftrace -e "kretprobe:kvm_arch_has_noncoherent_dma { printf("returned: %lx\n", retval); }"

观测的返回值都是 0

static bool need_emulate_wbinvd(struct kvm_vcpu *vcpu)
{
	return kvm_arch_has_noncoherent_dma(vcpu->kvm);
}

Guest 中只有启动的时候才会使用几次这个指令。

这个问题本身到没有什么，只是让我想起来了 DMA cache coherency

继续阅读手册

[ ] avic

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