Eric Northup wrote on 2013-02-21:
> On Tue, Feb 19, 2013 at 6:46 PM, Zhang, Yang Z <yang.z.zhang@xxxxxxxxx> wrote:
>>
>> Avi Kivity wrote on 2013-02-20:
>>> 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.
>> Linux uses IST for NMI, stack fault, machine-check, double fault and debug
>> interrupt . No external interrupt will use it.
>> This feature is only for external interrupt. So we don't need to check it
>> here.
>
> Would it be silly paranoia to BUG_ON(desc->ist) ?
I think the BUG_ON is reasonable. I will add it in next version.
Best regards,
Yang
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