linux-kernel - Re: [RFC PATCH 6/8] KVM: x86: Implement kvm_arch_{, pre_}vcpu_map

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Date: Wed, 6 Mar 2024 17:34:50 -0800
From: Isaku Yamahata <isaku.yamahata@...ux.intel.com>
To: David Matlack <dmatlack@...gle.com>
Cc: isaku.yamahata@...el.com, kvm@...r.kernel.org, isaku.yamahata@...il.com,
	linux-kernel@...r.kernel.org,
	Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Michael Roth <michael.roth@....com>,
	Federico Parola <federico.parola@...ito.it>,
	isaku.yamahata@...ux.intel.com
Subject: Re: [RFC PATCH 6/8] KVM: x86: Implement kvm_arch_{,
 pre_}vcpu_map_memory()

On Wed, Mar 06, 2024 at 04:30:58PM -0800,
David Matlack <dmatlack@...gle.com> wrote:

> On 2024-03-01 09:28 AM, isaku.yamahata@...el.com wrote:
> > From: Isaku Yamahata <isaku.yamahata@...el.com>
> > 
> > Wire KVM_MAP_MEMORY ioctl to kvm_mmu_map_tdp_page() to populate guest
> > memory.
> > 
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > ---
> >  arch/x86/kvm/x86.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 49 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 3b8cb69b04fa..6025c0e12d89 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -4660,6 +4660,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> >  	case KVM_CAP_VM_DISABLE_NX_HUGE_PAGES:
> >  	case KVM_CAP_IRQFD_RESAMPLE:
> >  	case KVM_CAP_MEMORY_FAULT_INFO:
> > +	case KVM_CAP_MAP_MEMORY:
> >  		r = 1;
> >  		break;
> >  	case KVM_CAP_EXIT_HYPERCALL:
> > @@ -5805,6 +5806,54 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
> >  	}
> >  }
> >  
> > +int kvm_arch_vcpu_pre_map_memory(struct kvm_vcpu *vcpu)
> > +{
> > +	return kvm_mmu_reload(vcpu);
> > +}
> 
> Why is the here and not kvm_arch_vcpu_map_memory()?

We can push down kvm_mmu_relaod into kvm_arch_vcpu_map_memory() under gpa loop.
Probably the inefficiency won't matter.

kvm_mmu_realod()
loop on gpa
  kvm_arch_vcpu_map_memory()

=>

loop on gpa
    kvm_arch_vcpu_map_memory()
      kvm_mmu_reload()
-- 
Isaku Yamahata <isaku.yamahata@...ux.intel.com>