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[PATCH 5/7] KVM: x86: Move kvm_set_apic_base() implementation to lapic.c (from x86.c)

Sean Christopherson posted 7 patches 1 year, 4 months ago
There is a newer version of this series
[PATCH 5/7] KVM: x86: Move kvm_set_apic_base() implementation to lapic.c (from x86.c)
Posted by Sean Christopherson 1 year, 4 months ago 
Move kvm_set_apic_base() to lapic.c so that the bulk of KVM's local APIC
code resides in lapic.c, regardless of whether or not KVM is emulating the
local APIC in-kernel.  This will also allow making various helpers visible
only to lapic.c.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/lapic.c | 21 +++++++++++++++++++++
 arch/x86/kvm/x86.c   | 21 ---------------------
 2 files changed, 21 insertions(+), 21 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index fe30f465611f..6239cfd89aad 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2628,6 +2628,27 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
 	}
 }
 
+int kvm_set_apic_base(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
+{
+	enum lapic_mode old_mode = kvm_get_apic_mode(vcpu);
+	enum lapic_mode new_mode = kvm_apic_mode(msr_info->data);
+	u64 reserved_bits = kvm_vcpu_reserved_gpa_bits_raw(vcpu) | 0x2ff |
+		(guest_cpuid_has(vcpu, X86_FEATURE_X2APIC) ? 0 : X2APIC_ENABLE);
+
+	if ((msr_info->data & reserved_bits) != 0 || new_mode == LAPIC_MODE_INVALID)
+		return 1;
+	if (!msr_info->host_initiated) {
+		if (old_mode == LAPIC_MODE_X2APIC && new_mode == LAPIC_MODE_XAPIC)
+			return 1;
+		if (old_mode == LAPIC_MODE_DISABLED && new_mode == LAPIC_MODE_X2APIC)
+			return 1;
+	}
+
+	kvm_lapic_set_base(vcpu, msr_info->data);
+	kvm_recalculate_apic_map(vcpu->kvm);
+	return 0;
+}
+
 void kvm_apic_update_apicv(struct kvm_vcpu *vcpu)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c70ee3b33b93..a2a2a6126e67 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -667,27 +667,6 @@ static void drop_user_return_notifiers(void)
 		kvm_on_user_return(&msrs->urn);
 }
 
-int kvm_set_apic_base(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
-{
-	enum lapic_mode old_mode = kvm_get_apic_mode(vcpu);
-	enum lapic_mode new_mode = kvm_apic_mode(msr_info->data);
-	u64 reserved_bits = kvm_vcpu_reserved_gpa_bits_raw(vcpu) | 0x2ff |
-		(guest_cpuid_has(vcpu, X86_FEATURE_X2APIC) ? 0 : X2APIC_ENABLE);
-
-	if ((msr_info->data & reserved_bits) != 0 || new_mode == LAPIC_MODE_INVALID)
-		return 1;
-	if (!msr_info->host_initiated) {
-		if (old_mode == LAPIC_MODE_X2APIC && new_mode == LAPIC_MODE_XAPIC)
-			return 1;
-		if (old_mode == LAPIC_MODE_DISABLED && new_mode == LAPIC_MODE_X2APIC)
-			return 1;
-	}
-
-	kvm_lapic_set_base(vcpu, msr_info->data);
-	kvm_recalculate_apic_map(vcpu->kvm);
-	return 0;
-}
-
 /*
  * Handle a fault on a hardware virtualization (VMX or SVM) instruction.
  *
-- 
2.47.0.rc1.288.g06298d1525-goog
Re: [PATCH 5/7] KVM: x86: Move kvm_set_apic_base() implementation to lapic.c (from x86.c)
Posted by Huang, Kai 1 year, 3 months ago 
On Wed, 2024-10-09 at 11:17 -0700, Sean Christopherson wrote:
> Move kvm_set_apic_base() to lapic.c so that the bulk of KVM's local APIC
> code resides in lapic.c, regardless of whether or not KVM is emulating the
> local APIC in-kernel.  This will also allow making various helpers visible
> only to lapic.c.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  arch/x86/kvm/lapic.c | 21 +++++++++++++++++++++
>  arch/x86/kvm/x86.c   | 21 ---------------------
>  2 files changed, 21 insertions(+), 21 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index fe30f465611f..6239cfd89aad 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2628,6 +2628,27 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
>  	}
>  }
>  
> +int kvm_set_apic_base(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> +{
> +	enum lapic_mode old_mode = kvm_get_apic_mode(vcpu);
> +	enum lapic_mode new_mode = kvm_apic_mode(msr_info->data);
> +	u64 reserved_bits = kvm_vcpu_reserved_gpa_bits_raw(vcpu) | 0x2ff |
> +		(guest_cpuid_has(vcpu, X86_FEATURE_X2APIC) ? 0 : X2APIC_ENABLE);
> +
> +	if ((msr_info->data & reserved_bits) != 0 || new_mode == LAPIC_MODE_INVALID)
> +		return 1;
> +	if (!msr_info->host_initiated) {
> +		if (old_mode == LAPIC_MODE_X2APIC && new_mode == LAPIC_MODE_XAPIC)
> +			return 1;
> +		if (old_mode == LAPIC_MODE_DISABLED && new_mode == LAPIC_MODE_X2APIC)
> +			return 1;
> +	}
> +
> +	kvm_lapic_set_base(vcpu, msr_info->data);
> +	kvm_recalculate_apic_map(vcpu->kvm);
> +	return 0;
> +}

Nit:

It is a little bit weird to use 'struct msr_data *msr_info' as function
parameter if kvm_set_apic_base() is in lapic.c.  Maybe we can change to take
apic_base and host_initialized directly.

A side gain is we can get rid of using the 'struct msr_data apic_base_msr' local
variable in __set_sregs_common() when calling kvm_apic_set_base():

static int __set_sregs_common(...)
{
        struct msr_data apic_base_msr;
	...

        apic_base_msr.data = sregs->apic_base;
        apic_base_msr.host_initiated = true;
        if (kvm_set_apic_base(vcpu, &apic_base_msr))
                return -EINVAL;
	...
}
Re: [PATCH 5/7] KVM: x86: Move kvm_set_apic_base() implementation to lapic.c (from x86.c)
Posted by Sean Christopherson 1 year, 3 months ago 
On Mon, Oct 14, 2024, Kai Huang wrote:
> On Wed, 2024-10-09 at 11:17 -0700, Sean Christopherson wrote:
> > Move kvm_set_apic_base() to lapic.c so that the bulk of KVM's local APIC
> > code resides in lapic.c, regardless of whether or not KVM is emulating the
> > local APIC in-kernel.  This will also allow making various helpers visible
> > only to lapic.c.
> > 
> > No functional change intended.
> > 
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > ---
> >  arch/x86/kvm/lapic.c | 21 +++++++++++++++++++++
> >  arch/x86/kvm/x86.c   | 21 ---------------------
> >  2 files changed, 21 insertions(+), 21 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > index fe30f465611f..6239cfd89aad 100644
> > --- a/arch/x86/kvm/lapic.c
> > +++ b/arch/x86/kvm/lapic.c
> > @@ -2628,6 +2628,27 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
> >  	}
> >  }
> >  
> > +int kvm_set_apic_base(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> > +{
> > +	enum lapic_mode old_mode = kvm_get_apic_mode(vcpu);
> > +	enum lapic_mode new_mode = kvm_apic_mode(msr_info->data);
> > +	u64 reserved_bits = kvm_vcpu_reserved_gpa_bits_raw(vcpu) | 0x2ff |
> > +		(guest_cpuid_has(vcpu, X86_FEATURE_X2APIC) ? 0 : X2APIC_ENABLE);
> > +
> > +	if ((msr_info->data & reserved_bits) != 0 || new_mode == LAPIC_MODE_INVALID)
> > +		return 1;
> > +	if (!msr_info->host_initiated) {
> > +		if (old_mode == LAPIC_MODE_X2APIC && new_mode == LAPIC_MODE_XAPIC)
> > +			return 1;
> > +		if (old_mode == LAPIC_MODE_DISABLED && new_mode == LAPIC_MODE_X2APIC)
> > +			return 1;
> > +	}
> > +
> > +	kvm_lapic_set_base(vcpu, msr_info->data);
> > +	kvm_recalculate_apic_map(vcpu->kvm);
> > +	return 0;
> > +}
> 
> Nit:
> 
> It is a little bit weird to use 'struct msr_data *msr_info' as function
> parameter if kvm_set_apic_base() is in lapic.c.  Maybe we can change to take
> apic_base and host_initialized directly.
> 
> A side gain is we can get rid of using the 'struct msr_data apic_base_msr' local
> variable in __set_sregs_common() when calling kvm_apic_set_base():

Ooh, nice.  I agree, it'd be better to pass in separate parameters.

Gah, and looking at this with fresh eyes reminded me why I even started poking at
this code in the first place.  Patch 1's changelog does a poor job of calling it
out, but the main impetus for this series was to avoid kvm_recalculate_apic_map()
when doing KVM_SET_SREGS without modifying APIC_BASE.  That's _mostly_ handled by
patch 1, but it doesn't completely fix things because if the map is already DIRTY,
then KVM will unnecessarily fall into kvm_recalculate_apic_map()'s slow path, even
though some other vCPU/task is responsible for refreshing the calculation.

I'll send a v2 with your suggested change, a better changelog for patch 1, and
another patch at the end to short-circuit kvm_apic_set_base() (not just the inner
helper) if the new value is the same as the old value.

Thanks Kai!

> static int __set_sregs_common(...)
> {
>         struct msr_data apic_base_msr;
> 	...
> 
>         apic_base_msr.data = sregs->apic_base;
>         apic_base_msr.host_initiated = true;
>         if (kvm_set_apic_base(vcpu, &apic_base_msr))
>                 return -EINVAL;
> 	...
> }
>
Re: [PATCH 5/7] KVM: x86: Move kvm_set_apic_base() implementation to lapic.c (from x86.c)
Posted by Sean Christopherson 1 year, 3 months ago 
On Mon, Oct 14, 2024, Sean Christopherson wrote:
> On Mon, Oct 14, 2024, Kai Huang wrote:
> > On Wed, 2024-10-09 at 11:17 -0700, Sean Christopherson wrote:
> > > Move kvm_set_apic_base() to lapic.c so that the bulk of KVM's local APIC
> > > code resides in lapic.c, regardless of whether or not KVM is emulating the
> > > local APIC in-kernel.  This will also allow making various helpers visible
> > > only to lapic.c.
> > > 
> > > No functional change intended.
> > > 
> > > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > > ---
> > >  arch/x86/kvm/lapic.c | 21 +++++++++++++++++++++
> > >  arch/x86/kvm/x86.c   | 21 ---------------------
> > >  2 files changed, 21 insertions(+), 21 deletions(-)
> > > 
> > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > > index fe30f465611f..6239cfd89aad 100644
> > > --- a/arch/x86/kvm/lapic.c
> > > +++ b/arch/x86/kvm/lapic.c
> > > @@ -2628,6 +2628,27 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
> > >  	}
> > >  }
> > >  
> > > +int kvm_set_apic_base(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> > > +{
> > > +	enum lapic_mode old_mode = kvm_get_apic_mode(vcpu);
> > > +	enum lapic_mode new_mode = kvm_apic_mode(msr_info->data);
> > > +	u64 reserved_bits = kvm_vcpu_reserved_gpa_bits_raw(vcpu) | 0x2ff |
> > > +		(guest_cpuid_has(vcpu, X86_FEATURE_X2APIC) ? 0 : X2APIC_ENABLE);
> > > +
> > > +	if ((msr_info->data & reserved_bits) != 0 || new_mode == LAPIC_MODE_INVALID)
> > > +		return 1;
> > > +	if (!msr_info->host_initiated) {
> > > +		if (old_mode == LAPIC_MODE_X2APIC && new_mode == LAPIC_MODE_XAPIC)
> > > +			return 1;
> > > +		if (old_mode == LAPIC_MODE_DISABLED && new_mode == LAPIC_MODE_X2APIC)
> > > +			return 1;
> > > +	}
> > > +
> > > +	kvm_lapic_set_base(vcpu, msr_info->data);
> > > +	kvm_recalculate_apic_map(vcpu->kvm);
> > > +	return 0;
> > > +}
> > 
> > Nit:
> > 
> > It is a little bit weird to use 'struct msr_data *msr_info' as function
> > parameter if kvm_set_apic_base() is in lapic.c.  Maybe we can change to take
> > apic_base and host_initialized directly.
> > 
> > A side gain is we can get rid of using the 'struct msr_data apic_base_msr' local
> > variable in __set_sregs_common() when calling kvm_apic_set_base():
> 
> Ooh, nice.  I agree, it'd be better to pass in separate parameters.
> 
> Gah, and looking at this with fresh eyes reminded me why I even started poking at
> this code in the first place.  Patch 1's changelog does a poor job of calling it
> out,

Duh, because patch 1 doesn't change any of that.  KVM already skips setting the
map DIRTY if neither MSR_IA32_APICBASE_ENABLE nor X2APIC_ENABLE is toggled.  So
it's really just the (IIRC, rare) collision with an already-dirty map that's nice
to avoid.

> but the main impetus for this series was to avoid kvm_recalculate_apic_map()
> when doing KVM_SET_SREGS without modifying APIC_BASE.  That's _mostly_ handled by
> patch 1, but it doesn't completely fix things because if the map is already DIRTY,
> then KVM will unnecessarily fall into kvm_recalculate_apic_map()'s slow path, even
> though some other vCPU/task is responsible for refreshing the calculation.
> 
> I'll send a v2 with your suggested change, a better changelog for patch 1, and
> another patch at the end to short-circuit kvm_apic_set_base() (not just the inner
> helper) if the new value is the same as the old value.
> 
> Thanks Kai!
> 
> > static int __set_sregs_common(...)
> > {
> >         struct msr_data apic_base_msr;
> > 	...
> > 
> >         apic_base_msr.data = sregs->apic_base;
> >         apic_base_msr.host_initiated = true;
> >         if (kvm_set_apic_base(vcpu, &apic_base_msr))
> >                 return -EINVAL;
> > 	...
> > }
> >
Re: [PATCH 5/7] KVM: x86: Move kvm_set_apic_base() implementation to lapic.c (from x86.c)
Posted by Huang, Kai 1 year, 3 months ago 

On 15/10/2024 8:40 am, Sean Christopherson wrote:
> On Mon, Oct 14, 2024, Sean Christopherson wrote:
>> On Mon, Oct 14, 2024, Kai Huang wrote:
>>> On Wed, 2024-10-09 at 11:17 -0700, Sean Christopherson wrote:
>>>> Move kvm_set_apic_base() to lapic.c so that the bulk of KVM's local APIC
>>>> code resides in lapic.c, regardless of whether or not KVM is emulating the
>>>> local APIC in-kernel.  This will also allow making various helpers visible
>>>> only to lapic.c.
>>>>
>>>> No functional change intended.
>>>>
>>>> Signed-off-by: Sean Christopherson <seanjc@google.com>
>>>> ---
>>>>   arch/x86/kvm/lapic.c | 21 +++++++++++++++++++++
>>>>   arch/x86/kvm/x86.c   | 21 ---------------------
>>>>   2 files changed, 21 insertions(+), 21 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>>>> index fe30f465611f..6239cfd89aad 100644
>>>> --- a/arch/x86/kvm/lapic.c
>>>> +++ b/arch/x86/kvm/lapic.c
>>>> @@ -2628,6 +2628,27 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
>>>>   	}
>>>>   }
>>>>   
>>>> +int kvm_set_apic_base(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>>> +{
>>>> +	enum lapic_mode old_mode = kvm_get_apic_mode(vcpu);
>>>> +	enum lapic_mode new_mode = kvm_apic_mode(msr_info->data);
>>>> +	u64 reserved_bits = kvm_vcpu_reserved_gpa_bits_raw(vcpu) | 0x2ff |
>>>> +		(guest_cpuid_has(vcpu, X86_FEATURE_X2APIC) ? 0 : X2APIC_ENABLE);
>>>> +
>>>> +	if ((msr_info->data & reserved_bits) != 0 || new_mode == LAPIC_MODE_INVALID)
>>>> +		return 1;
>>>> +	if (!msr_info->host_initiated) {
>>>> +		if (old_mode == LAPIC_MODE_X2APIC && new_mode == LAPIC_MODE_XAPIC)
>>>> +			return 1;
>>>> +		if (old_mode == LAPIC_MODE_DISABLED && new_mode == LAPIC_MODE_X2APIC)
>>>> +			return 1;
>>>> +	}
>>>> +
>>>> +	kvm_lapic_set_base(vcpu, msr_info->data);
>>>> +	kvm_recalculate_apic_map(vcpu->kvm);
>>>> +	return 0;
>>>> +}
>>>
>>> Nit:
>>>
>>> It is a little bit weird to use 'struct msr_data *msr_info' as function
>>> parameter if kvm_set_apic_base() is in lapic.c.  Maybe we can change to take
>>> apic_base and host_initialized directly.
>>>
>>> A side gain is we can get rid of using the 'struct msr_data apic_base_msr' local
>>> variable in __set_sregs_common() when calling kvm_apic_set_base():
>>
>> Ooh, nice.  I agree, it'd be better to pass in separate parameters.
>>
>> Gah, and looking at this with fresh eyes reminded me why I even started poking at
>> this code in the first place.  Patch 1's changelog does a poor job of calling it
>> out,
> 
> Duh, because patch 1 doesn't change any of that.  KVM already skips setting the
> map DIRTY if neither MSR_IA32_APICBASE_ENABLE nor X2APIC_ENABLE is toggled.  So
> it's really just the (IIRC, rare) collision with an already-dirty map that's nice
> to avoid.
> 

I think if the map is already dirty, the other thread that makes the map 
dirty must be responsible for calling kvm_recalculate_apic_map() after that.

For updating 'apic_base' path, IIUC it makes sense anyway to avoid 
everything when 'apic_base' doesn't change.

Calling kvm_recalculate_apic_map() when 'apic_base' is not changed has 
no harm, but logically I don't think there's need to do that, even the 
map is already dirty.

Patchew 2.1-devel-b67e4c2

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