linux-kernel - Re: [PATCH 06/10] KVM/nVMX: Use kvm_vcpu_map when mapping the virtual APIC page

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Date:   Thu, 12 Apr 2018 22:23:05 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     KarimAllah Ahmed <karahmed@...zon.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org, hpa@...or.com,
        jmattson@...gle.com, mingo@...hat.com, rkrcmar@...hat.com,
        tglx@...utronix.de
Subject: Re: [PATCH 06/10] KVM/nVMX: Use kvm_vcpu_map when mapping the virtual
 APIC page

On 12/04/2018 19:57, Sean Christopherson wrote:
> On Thu, Apr 12, 2018 at 04:38:39PM +0200, Paolo Bonzini wrote:
>> On 21/02/2018 18:47, KarimAllah Ahmed wrote:
>>> +
>>> +		if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcs12->virtual_apic_page_addr), map))
>>> +			vmcs_write64(VIRTUAL_APIC_PAGE_ADDR, gfn_to_gpa(map->pfn));
>>
>> This should in principle be pfn_to_hpa.  However, pfn_to_hpa is unused;
>> let's just remove it and do "<< PAGE_SHIFT".  Unlike gfn_to_gpa, where
>> in principle the shift could be different, pfn_to_hpa is *by definition*
>> a shift left by PAGE_SHIFT.
> 
> Any reason not to use PFN_PHYS instead of the handcoded shift?

That works too of course.  It's just not used much (or at all?) in KVM.

Paolo