On Tue, Feb 19, 2013 at 3:39 PM, Yang Zhang <yang.z.zhang@xxxxxxxxx> wrote:
> From: Yang Zhang <yang.z.zhang@xxxxxxxxx>
>
> The "acknowledge interrupt on exit" feature controls processor behavior
> for external interrupt acknowledgement. When this control is set, the
> processor acknowledges the interrupt controller to acquire the
> interrupt vector on VM exit.
>
> After enabling this feature, an interrupt which arrived when target cpu is
> running in vmx non-root mode will be handled by vmx handler instead of handler
> in idt. Currently, vmx handler only fakes an interrupt stack and jump to idt
> table to let real handler to handle it. Further, we will recognize the interrupt
> and only delivery the interrupt which not belong to current vcpu through idt table.
> The interrupt which belonged to current vcpu will be handled inside vmx handler.
> This will reduce the interrupt handle cost of KVM.
>
> Also, interrupt enable logic is changed if this feature is turnning on:
> Before this patch, hypervior call local_irq_enable() to enable it directly.
> Now IF bit is set on interrupt stack frame, and will be enabled on a return from
> interrupt handler if exterrupt interrupt exists. If no external interrupt, still
> call local_irq_enable() to enable it.
>
> Refer to Intel SDM volum 3, chapter 33.2.
>
> +static void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
> +{
> + u32 exit_intr_info = vmcs_read32(VM_EXIT_INTR_INFO);
> +
> + /*
> + * If external interrupt exists, IF bit is set in rflags/eflags on the
> + * interrupt stack frame, and interrupt will be enabled on a return
> + * from interrupt handler.
> + */
> + if ((exit_intr_info & (INTR_INFO_VALID_MASK | INTR_INFO_INTR_TYPE_MASK))
> + == (INTR_INFO_VALID_MASK | INTR_TYPE_EXT_INTR)) {
> + unsigned int vector;
> + unsigned long entry;
> + gate_desc *desc;
> + struct vcpu_vmx *vmx = to_vmx(vcpu);
> +
> + vector = exit_intr_info & INTR_INFO_VECTOR_MASK;
> +#ifdef CONFIG_X86_64
> + desc = (void *)vmx->host_idt_base + vector * 16;
> +#else
> + desc = (void *)vmx->host_idt_base + vector * 8;
> +#endif
> +
> + entry = gate_offset(*desc);
> + asm(
> + "mov %0, %%" _ASM_DX " \n\t"
> +#ifdef CONFIG_X86_64
> + "mov %%" _ASM_SP ", %%" _ASM_BX " \n\t"
> + "and $0xfffffffffffffff0, %%" _ASM_SP " \n\t"
> + "mov %%ss, %%" _ASM_AX " \n\t"
> + "push %%" _ASM_AX " \n\t"
> + "push %%" _ASM_BX " \n\t"
> +#endif
Are we sure no interrupts are using the IST feature? I guess it's unlikely.
> + "pushf \n\t"
> + "pop %%" _ASM_AX " \n\t"
> + "or $0x200, %%" _ASM_AX " \n\t"
> + "push %%" _ASM_AX " \n\t"
Can simplify to pushf; orl $0x200, %%rsp.
> + "mov %%cs, %%" _ASM_AX " \n\t"
> + "push %%" _ASM_AX " \n\t"
push %%cs
> + "push intr_return \n\t"
push $1f. Or even combine with the next instruction, and call %rdx.
> + "jmp *%% " _ASM_DX " \n\t"
> + "1: \n\t"
> + ".pushsection .rodata \n\t"
> + ".global intr_return \n\t"
> + "intr_return: " _ASM_PTR " 1b \n\t"
> + ".popsection \n\t"
> + : : "m"(entry) :
> +#ifdef CONFIG_X86_64
> + "rax", "rbx", "rdx"
> +#else
> + "eax", "edx"
> +#endif
> + );
> + } else
> + local_irq_enable();
> +}
> +
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