Eric Northup wrote on 2013-02-21: > On Tue, Feb 19, 2013 at 6:46 PM, Zhang, Yang Z <yang.z.zh...@intel.com> wrote: >> >> Avi Kivity wrote on 2013-02-20: >>> On Tue, Feb 19, 2013 at 3:39 PM, Yang Zhang <yang.z.zh...@intel.com> >>> wrote: >>>> From: Yang Zhang <yang.z.zh...@intel.com> >>>> >>>> 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 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html