Re: [PATCH 4/4] kvm, mem-hotplug: Update apic access page when it is migrated.

[Tang Chen <tangchen@cn.fujitsu.com>]

Hi Gleb,

Thanks for the advices. Please see below.

On 07/03/2014 09:55 PM, Gleb Natapov wrote:
......
>> @@ -575,6 +575,7 @@ struct kvm_arch {
>>
>>   	unsigned int tss_addr;
>>   	struct page *apic_access_page;
>> +	bool apic_access_page_migrated;
> Better have two requests KVM_REQ_APIC_PAGE_MAP, KVM_REQ_APIC_PAGE_UNMAP IMO.
>

vcpu->requests is an unsigned long, and we can only has 64 requests. Isn't
adding two requests for apic page and another similar two for ept page too
many ?  Not sure.

>>
>>   	gpa_t wall_clock;
>>
>> @@ -739,6 +740,7 @@ struct kvm_x86_ops {
>>   	void (*hwapic_isr_update)(struct kvm *kvm, int isr);
>>   	void (*load_eoi_exitmap)(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap);
>>   	void (*set_virtual_x2apic_mode)(struct kvm_vcpu *vcpu, bool set);
>> +	void (*set_apic_access_page_addr)(struct kvm *kvm, hpa_t hpa);
>>   	void (*deliver_posted_interrupt)(struct kvm_vcpu *vcpu, int vector);
>>   	void (*sync_pir_to_irr)(struct kvm_vcpu *vcpu);
>>   	int (*set_tss_addr)(struct kvm *kvm, unsigned int addr);
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index c0d72f6..a655444 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -3436,6 +3436,21 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa, u32 error_code,
>>   		kvm_make_request(KVM_REQ_MIGRATE_EPT, vcpu);
>>   	}
>>
>> +	if (gpa == VMX_APIC_ACCESS_PAGE_ADDR&&
>> +	    vcpu->kvm->arch.apic_access_page_migrated) {
> Why check arch.apic_access_page_migrated here? Isn't it enough that the fault is on apic
> address.
>

True. It's enough. Followed.

>> +		int i;
>> +
>> +		vcpu->kvm->arch.apic_access_page_migrated = false;
>> +
>> +		/*
>> +		 * We need update APIC_ACCESS_ADDR pointer in each VMCS of
>> +		 * all the online vcpus.
>> +		 */
>> +		for (i = 0; i<  atomic_read(&vcpu->kvm->online_vcpus); i++)
>> +			kvm_make_request(KVM_REQ_MIGRATE_APIC,
>> +					 vcpu->kvm->vcpus[i]);
> make_all_cpus_request(). You need to kick all vcpus from a guest mode.
>

OK, followed. But would you please explain more about this. :)
Why need to kick all vcpus from guest mode when making request to all 
vcpus ?

>> +	}
>> +
>>   	spin_unlock(&vcpu->kvm->mmu_lock);
>>
>>   	return r;
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index c336cb3..abc152f 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -3988,7 +3988,7 @@ static int alloc_apic_access_page(struct kvm *kvm)
>>   	if (r)
>>   		goto out;
>>
>> -	page = gfn_to_page(kvm, VMX_APIC_ACCESS_PAGE_ADDR>>  PAGE_SHIFT);
>> +	page = gfn_to_page_no_pin(kvm, VMX_APIC_ACCESS_PAGE_ADDR>>  PAGE_SHIFT);
>>   	if (is_error_page(page)) {
>>   		r = -EFAULT;
>>   		goto out;
>> @@ -7075,6 +7075,12 @@ static void vmx_set_virtual_x2apic_mode(struct kvm_vcpu *vcpu, bool set)
>>   	vmx_set_msr_bitmap(vcpu);
>>   }
>>
>> +static void vmx_set_apic_access_page_addr(struct kvm *kvm, hpa_t hpa)
>> +{
>> +	if (vm_need_virtualize_apic_accesses(kvm))
> This shouldn't even been called if apic access page is not supported. Nor
> mmu_notifier path neither tdp_page_fault path should ever see 0xfee00000
> address. BUG() is more appropriate here.
>

I don't quite understand. Why calling this function here will leed to bug ?
(Sorry, I'm not quite understand the internal of KVM. Please help.)

>
>> +		vmcs_write64(APIC_ACCESS_ADDR, hpa);
>> +}
>> +
>>   static void vmx_hwapic_isr_update(struct kvm *kvm, int isr)
>>   {
>>   	u16 status;
>> @@ -8846,6 +8852,7 @@ static struct kvm_x86_ops vmx_x86_ops = {
>>   	.enable_irq_window = enable_irq_window,
>>   	.update_cr8_intercept = update_cr8_intercept,
>>   	.set_virtual_x2apic_mode = vmx_set_virtual_x2apic_mode,
>> +	.set_apic_access_page_addr = vmx_set_apic_access_page_addr,
> svm needs that too.
>

OK, will add one for svm.

>>   	.vm_has_apicv = vmx_vm_has_apicv,
>>   	.load_eoi_exitmap = vmx_load_eoi_exitmap,
>>   	.hwapic_irr_update = vmx_hwapic_irr_update,
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index a26524f..14e7174 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -5943,6 +5943,24 @@ static void vcpu_migrated_page_update_ept(struct kvm_vcpu *vcpu)
>>   	}
>>   }
>>
>> +static void vcpu_migrated_page_update_apic(struct kvm_vcpu *vcpu)
>> +{
>> +	struct kvm *kvm = vcpu->kvm;
>> +
>> +	if (kvm->arch.apic_access_page_migrated) {
>> +		if (kvm->arch.apic_access_page)
>> +			kvm->arch.apic_access_page = pfn_to_page(0);
> All vcpus will access apic_access_page without locking here. May be
> set kvm->arch.apic_access_page to zero in mmu_notifier and here call
>   kvm_x86_ops->set_apic_access_page_addr(kvm, kvm->arch.apic_access_page);
>

I'm a little confused. apic access page's phys_addr is stored in vmcs, and
I think it will be used by vcpu directly to access the physical page.
Setting kvm->arch.apic_access_page to zero will not stop it, right ?

I'm wondering what happens when apic page is migrated, but the vmcs is 
still
holding its old phys_addr before the vcpu request is handled.

>
>> +		kvm_x86_ops->set_apic_access_page_addr(kvm, 0x0ull);
>> +	} else {
>> +		struct page *page;
>> +		page = gfn_to_page_no_pin(kvm,
>> +				VMX_APIC_ACCESS_PAGE_ADDR>>  PAGE_SHIFT);
>> +		kvm->arch.apic_access_page = page;
> Same, set it during tdp fault when page is mapped.
>
>> +		kvm_x86_ops->set_apic_access_page_addr(kvm,
>> +						       page_to_phys(page));
>> +	}
>> +}
>> +
>>   /*
>>    * Returns 1 to let __vcpu_run() continue the guest execution loop without
>>    * exiting to the userspace.  Otherwise, the value will be returned to the
>> @@ -6005,6 +6023,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>>   			vcpu_scan_ioapic(vcpu);
>>   		if (kvm_check_request(KVM_REQ_MIGRATE_EPT, vcpu))
>>   			vcpu_migrated_page_update_ept(vcpu);
>> +		if (kvm_check_request(KVM_REQ_MIGRATE_APIC, vcpu))
>> +			vcpu_migrated_page_update_apic(vcpu);
>>   	}
>>
>>   	if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {
>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
>> index 4b7e51a..e2ad65e 100644
>> --- a/include/linux/kvm_host.h
>> +++ b/include/linux/kvm_host.h
>> @@ -137,6 +137,7 @@ static inline bool is_error_page(struct page *page)
>>   #define KVM_REQ_ENABLE_IBS        23
>>   #define KVM_REQ_DISABLE_IBS       24
>>   #define KVM_REQ_MIGRATE_EPT       25
>> +#define KVM_REQ_MIGRATE_APIC      26
>>
>>   #define KVM_USERSPACE_IRQ_SOURCE_ID		0
>>   #define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID	1
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index d271e89..f06438c 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -54,6 +54,7 @@
>>   #include<asm/io.h>
>>   #include<asm/uaccess.h>
>>   #include<asm/pgtable.h>
>> +#include<asm/vmx.h>
>>
>>   #include "coalesced_mmio.h"
>>   #include "async_pf.h"
>> @@ -300,6 +301,20 @@ static void kvm_mmu_notifier_invalidate_page(struct mmu_notifier *mn,
>>   		kvm_make_request(KVM_REQ_MIGRATE_EPT, kvm->vcpus[0]);
>>   	}
>>
>> +	if (address ==
>> +	    gfn_to_hva(kvm, VMX_APIC_ACCESS_PAGE_ADDR>>  PAGE_SHIFT)) {
>> +		int i;
>> +
>> +		kvm->arch.apic_access_page_migrated = true;
>> +
>> +		/*
>> +		 * We need update APIC_ACCESS_ADDR pointer in each VMCS of
>> +		 * all the online vcpus.
>> +		 */
>> +		for (i = 0; i<  atomic_read(&kvm->online_vcpus); i++)
>> +			kvm_make_request(KVM_REQ_MIGRATE_APIC, kvm->vcpus[i]);
>> +	}
> make_all_cpus_request()
>
> Also you need to drop put_page(kvm->arch.apic_access_page); from x86.c

Yes. Forgot it.

Thanks. :)

>> +
>>   	spin_unlock(&kvm->mmu_lock);
>>   	srcu_read_unlock(&kvm->srcu, idx);
>>   }
>> --
>> 1.8.3.1
>>
>
> --
> 			Gleb.
> .
>