[Qemu-devel] INVLPG and IPI emulation in KVM

[Qemu-devel] INVLPG and IPI emulation in KVM

[Xin Tong]

I am investigating how INVLPG is emulated in kvm. It turns out that it calls

kvm_mmu_invlpg
   kvm_mmu_flush_tlb
     kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);

and the kvm_make_request set the vcpu->requests bit to high, when the
guest os resumes, it handles the bit. I have 2 questions


1. How does the make_request mechanism work ? how does the guest
handle the requests ?
2. INVLPG invalidates a tlb entry, it is typically used when the page
table changes. However, an ipi is typically used to invalidate the tlb
entries in other processor cores, However, i can not find the
emulation code for IPI instruction.

Thanks

Xin

Re: INVLPG and IPI emulation in KVM

[Avi Kivity]

On 11/13/2011 02:27 PM, Xin Tong wrote:
> I am investigating how INVLPG is emulated in kvm. 

You're on the wrong list.

> It turns out that it calls
>
> kvm_mmu_invlpg
>    kvm_mmu_flush_tlb
>      kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
>
> and the kvm_make_request set the vcpu->requests bit to high, when the
> guest os resumes, it handles the bit. I have 2 questions
>
>
> 1. How does the make_request mechanism work ? 

See vcpu_enter_guest().

> how does the guest
> handle the requests ?

The guest never sees them, this is all internal to kvm.

> 2. INVLPG invalidates a tlb entry, it is typically used when the page
> table changes. However, an ipi is typically used to invalidate the tlb
> entries in other processor cores, However, i can not find the
> emulation code for IPI instruction.

There is no IPI instruction, see lapic.c:apic_send_ipi().

-- 
error compiling committee.c: too many arguments to function

Re: [Qemu-devel] INVLPG and IPI emulation in KVM

[Avi Kivity]

On 11/13/2011 02:27 PM, Xin Tong wrote:
> I am investigating how INVLPG is emulated in kvm. 

You're on the wrong list.

> It turns out that it calls
>
> kvm_mmu_invlpg
>    kvm_mmu_flush_tlb
>      kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
>
> and the kvm_make_request set the vcpu->requests bit to high, when the
> guest os resumes, it handles the bit. I have 2 questions
>
>
> 1. How does the make_request mechanism work ? 

See vcpu_enter_guest().

> how does the guest
> handle the requests ?

The guest never sees them, this is all internal to kvm.

> 2. INVLPG invalidates a tlb entry, it is typically used when the page
> table changes. However, an ipi is typically used to invalidate the tlb
> entries in other processor cores, However, i can not find the
> emulation code for IPI instruction.

There is no IPI instruction, see lapic.c:apic_send_ipi().

-- 
error compiling committee.c: too many arguments to function