RE: [PATCH] KVM: VMX: enable acknowledge interupt on vmexit

Zhang, Yang Z
2013-01-17T06:34:53Z

Gleb Natapov wrote on 2013-01-17:
> On Thu, Jan 17, 2013 at 01:36:36AM +0000, Zhang, Yang Z wrote:
>> Gleb Natapov wrote on 2013-01-16:
>>> On Wed, Jan 16, 2013 at 05:00:48PM +0800, Yang Zhang wrote:
>>>> From: Yang Zhang <yang.z.zhang@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.
>>>>
>>>> This feature is required by Posted Interrupt. It will be turnned on only
>>>> when posted interrupt is enabled.
>>>>
>>> Why? Always enable it. It is faster than current approach.
>> I don't think it will faster. It should be same.
>>
> Interrupt delivered->vmexit->interrupt enabled->interrupt
> redelivered->acked->dispatched through idt.
>
> vs
>
> Interrupt delivered->acked->vmexit->dispatched through idt.
>
> Anyway even if it is not slower it is better to use the same code path
> to make sure it is well tested.
Ok.

>>>> Refer to Intel SDM volum 3, chapter 33.2.
>>>>
>>> Please CC H. Peter Anvin <hpa@linux.intel.com> on the next version.
>>>
>>>> Signed-off-by: Yang Zhang <yang.z.zhang@Intel.com>
>>>> ---
>>>> arch/x86/kvm/vmx.c | 51
>>>> +++++++++++++++++++++++++++++++++++++++++++++++++-- 1 files changed,
>>>> 49 insertions(+), 2 deletions(-)
>>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>>> index dd2a85c..d1ed9ae 100644
>>>> --- a/arch/x86/kvm/vmx.c
>>>> +++ b/arch/x86/kvm/vmx.c
>>>> @@ -2565,7 +2565,7 @@ static __init int setup_vmcs_config(struct
>>> vmcs_config *vmcs_conf)
>>>> #ifdef CONFIG_X86_64
>>>> min |= VM_EXIT_HOST_ADDR_SPACE_SIZE;
>>>> #endif
>>>> - opt = VM_EXIT_SAVE_IA32_PAT | VM_EXIT_LOAD_IA32_PAT;
>>>> + opt = VM_EXIT_SAVE_IA32_PAT | VM_EXIT_LOAD_IA32_PAT |
>>> VM_EXIT_ACK_INTR_ON_EXIT;
>>>> if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_EXIT_CTLS,
>>>> &_vmexit_control) < 0) return -EIO; @@ -3926,7 +3926,7 @@
>>>> static int vmx_vcpu_setup(struct vcpu_vmx *vmx) ++vmx->nmsrs;
> }
>>>> - vmcs_write32(VM_EXIT_CONTROLS, vmcs_config.vmexit_ctrl);
>>>> + vmcs_write32(VM_EXIT_CONTROLS, vmcs_config.vmexit_ctrl &
>>>> ~VM_EXIT_ACK_INTR_ON_EXIT);
>>>>
>>>> /* 22.2.1, 20.8.1 */
>>>> vmcs_write32(VM_ENTRY_CONTROLS, vmcs_config.vmentry_ctrl);
>>>> @@ -6096,6 +6096,52 @@ static void vmx_complete_atomic_exit(struct
>>> vcpu_vmx *vmx)
>>>> }
>>>> }
>>>> + +static noinline void vmx_handle_external_intr(struct kvm_vcpu
>>>> *vcpu) +{ + u32 exit_intr_info = vmcs_read32(VM_EXIT_INTR_INFO); +
>>>> + if ((exit_intr_info & INTR_INFO_INTR_TYPE_MASK) ==
>>>> INTR_TYPE_EXT_INTR && + (exit_intr_info & INTR_INFO_VALID_MASK) )
>>>> {
>>> 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;
>>>> + struct desc_ptr dt;
>>>> + gate_desc *desc;
>>>> +
>>>> + native_store_idt(&dt);
>>> This does not change. Store it in vcpu during vcpu creation instead of
>>> reading it each time.
>> Right. It will reduce the cost.
>>
>>>> +
>>>> + vector = exit_intr_info & INTR_INFO_VECTOR_MASK;
>>>> + desc = (void *)dt.address + vector * 16;
>>>> +
>>>> + entry = gate_offset(*desc);
>>>> + asm(
>>>> + "mov %0, %%" _ASM_DX "\n\t"
>>>> + "mov %%" _ASM_SP ", %%" _ASM_BX "\n\t"
>>>> +#ifdef CONFIG_X86_64
>>>> + "and $0xfffffffffffffff0, %%" _ASM_SP "\n\t"
>>>> +#endif
>>>> + "mov %%ss, %%" _ASM_AX "\n\t"
>>>> + "push %%" _ASM_AX "\n\t"
>>>> + "push %%" _ASM_BX "\n\t"
>>> For 32bit you do not need to save ss:esp.
>> You are right. No need to save it for 32bit.
>>
>>>> + "pushf\n\t"
>>>> + "mov %%cs, %%" _ASM_AX "\n\t"
>>>> + "push %%" _ASM_AX "\n\t"
>>>> + "push intr_return\n\t"
>>>> + "jmp *%% " _ASM_DX "\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", "ebx", "edx"
>>>> +#endif
>>>> + );
>>>> + }
>>>> +}
>>>> +
>>>> static void vmx_recover_nmi_blocking(struct vcpu_vmx *vmx)
>>>> {
>>>> u32 exit_intr_info;
>>>> @@ -6431,6 +6477,7 @@ static void __noclone vmx_vcpu_run(struct
>>> kvm_vcpu *vcpu)
>>>> vmx_complete_atomic_exit(vmx);
>>>> vmx_recover_nmi_blocking(vmx);
>>>> vmx_complete_interrupts(vmx);
>>>> + vmx_handle_external_intr(vcpu);
>>> This should be done just before enabling interrupts, otherwise we are
>>> taking an interrupt before vmexit is fully complete.
>> How about to put it just after set vcpu->mode to OUTSIDE_GUEST_MODE? At
>> that point, the vmexit is considered as fully complete.
>>
> As I said, right before local_irq_enable().
Ok.

Best regards,
Yang