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

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Message-ID: <d09669af3cc7758c740f9860f7f1f2ab5998eb3d.camel@intel.com>
Date: Mon, 14 Oct 2024 12:09:28 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "pbonzini@...hat.com" <pbonzini@...hat.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/7] KVM: x86: Move kvm_set_apic_base() implementation to
 lapic.c (from x86.c)

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@...gle.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;
	...
}