Re: [PATCH v5 07/13] KVM/nVMX: Use kvm_vcpu_map when mapping the virtual APIC page

["Raslan, KarimAllah" <karahmed@amazon.de>]

On Wed, 2019-01-23 at 12:57 -0500, Konrad Rzeszutek Wilk wrote:
> On Wed, Jan 09, 2019 at 10:42:07AM +0100, KarimAllah Ahmed wrote:
> > 
> > Use kvm_vcpu_map when mapping the virtual APIC page since using
> > kvm_vcpu_gpa_to_page() and kmap() will only work for guest memory that has
> > a "struct page".
> > 
> > One additional semantic change is that the virtual host mapping lifecycle
> > has changed a bit. It now has the same lifetime of the pinning of the
> > virtual APIC page on the host side.
> 
> Could you expand a bit on the 'same lifetime .. on the host side'  to be
> obvious for folks what exactly the semantic is?
> 
> And how does this ring with this comment:
> > 
> > 
> > Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
> > ---
> > v4 -> v5:
> > - unmap with dirty flag
> > 
> > v1 -> v2:
> > - Do not change the lifecycle of the mapping (pbonzini)
> 
> .. Where Paolo does not want the semantics of the mapping to be changed?
> 
> Code wise feel free to smack my Reviewed-by on it, but obviously the
> question on the above comment needs to be resolved.

Ah, right. So there was two life-cycle changes:

1- Lazily unmap the mapping and only do it on: a) release b) if the gfn is 
   different. This was done as an optimization (i.e. cache of a single entry). 
   This is the first life-cycle change that Paolo asked me to do seperately and
   suggested to create a PFN cache instead. This has indeed been dropped
   between v1 -> v2 switch.

2- The life-cycle change now is the fact that the kvm_vcpu_map interface does: 
   a) map to a virtual address b) translate a gfn to a pfn.

   The original code was doing the kmap in one location and the gfn_to_page in
   another. Using kvm_vcpu_map means that both kmap+gfn_to_page will be tied 
   together and will not be done seperately. So far no one complained about
   this one so I kept it :D

> 
> Thank you.
> 
> > 
> > - Use pfn_to_hpa instead of gfn_to_gpa
> > ---
> >  arch/x86/kvm/vmx/nested.c | 32 +++++++++++---------------------
> >  arch/x86/kvm/vmx/vmx.c    |  5 ++---
> >  arch/x86/kvm/vmx/vmx.h    |  2 +-
> >  3 files changed, 14 insertions(+), 25 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > index 4127ad9..dcff99d 100644
> > --- a/arch/x86/kvm/vmx/nested.c
> > +++ b/arch/x86/kvm/vmx/nested.c
> > @@ -229,10 +229,7 @@ static void free_nested(struct kvm_vcpu *vcpu)
> >  		kvm_release_page_dirty(vmx->nested.apic_access_page);
> >  		vmx->nested.apic_access_page = NULL;
> >  	}
> > -	if (vmx->nested.virtual_apic_page) {
> > -		kvm_release_page_dirty(vmx->nested.virtual_apic_page);
> > -		vmx->nested.virtual_apic_page = NULL;
> > -	}
> > +	kvm_vcpu_unmap(&vmx->nested.virtual_apic_map, true);
> >  	if (vmx->nested.pi_desc_page) {
> >  		kunmap(vmx->nested.pi_desc_page);
> >  		kvm_release_page_dirty(vmx->nested.pi_desc_page);
> > @@ -2817,6 +2814,7 @@ static void nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
> >  {
> >  	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> >  	struct vcpu_vmx *vmx = to_vmx(vcpu);
> > +	struct kvm_host_map *map;
> >  	struct page *page;
> >  	u64 hpa;
> >  
> > @@ -2849,11 +2847,7 @@ static void nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
> >  	}
> >  
> >  	if (nested_cpu_has(vmcs12, CPU_BASED_TPR_SHADOW)) {
> > -		if (vmx->nested.virtual_apic_page) { /* shouldn't happen */
> > -			kvm_release_page_dirty(vmx->nested.virtual_apic_page);
> > -			vmx->nested.virtual_apic_page = NULL;
> > -		}
> > -		page = kvm_vcpu_gpa_to_page(vcpu, vmcs12->virtual_apic_page_addr);
> > +		map = &vmx->nested.virtual_apic_map;
> >  
> >  		/*
> >  		 * If translation failed, VM entry will fail because
> > @@ -2868,11 +2862,9 @@ static void nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
> >  		 * control.  But such a configuration is useless, so
> >  		 * let's keep the code simple.
> >  		 */
> > -		if (!is_error_page(page)) {
> > -			vmx->nested.virtual_apic_page = page;
> > -			hpa = page_to_phys(vmx->nested.virtual_apic_page);
> > -			vmcs_write64(VIRTUAL_APIC_PAGE_ADDR, hpa);
> > -		}
> > +		if (!kvm_vcpu_map(vcpu, gpa_to_gfn(vmcs12->virtual_apic_page_addr), map))
> > +			vmcs_write64(VIRTUAL_APIC_PAGE_ADDR, pfn_to_hpa(map->pfn));
> > +
> >  	}
> >  
> >  	if (nested_cpu_has_posted_intr(vmcs12)) {
> > @@ -3279,11 +3271,12 @@ static void vmx_complete_nested_posted_interrupt(struct kvm_vcpu *vcpu)
> >  
> >  	max_irr = find_last_bit((unsigned long *)vmx->nested.pi_desc->pir, 256);
> >  	if (max_irr != 256) {
> > -		vapic_page = kmap(vmx->nested.virtual_apic_page);
> > +		vapic_page = vmx->nested.virtual_apic_map.hva;
> > +		if (!vapic_page)
> > +			return;
> > +
> >  		__kvm_apic_update_irr(vmx->nested.pi_desc->pir,
> >  			vapic_page, &max_irr);
> > -		kunmap(vmx->nested.virtual_apic_page);
> > -
> >  		status = vmcs_read16(GUEST_INTR_STATUS);
> >  		if ((u8)max_irr > ((u8)status & 0xff)) {
> >  			status &= ~0xff;
> > @@ -3917,10 +3910,7 @@ void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
> >  		kvm_release_page_dirty(vmx->nested.apic_access_page);
> >  		vmx->nested.apic_access_page = NULL;
> >  	}
> > -	if (vmx->nested.virtual_apic_page) {
> > -		kvm_release_page_dirty(vmx->nested.virtual_apic_page);
> > -		vmx->nested.virtual_apic_page = NULL;
> > -	}
> > +	kvm_vcpu_unmap(&vmx->nested.virtual_apic_map, true);
> >  	if (vmx->nested.pi_desc_page) {
> >  		kunmap(vmx->nested.pi_desc_page);
> >  		kvm_release_page_dirty(vmx->nested.pi_desc_page);
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index 71d88df..e13308e 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -3627,14 +3627,13 @@ static bool vmx_guest_apic_has_interrupt(struct kvm_vcpu *vcpu)
> >  
> >  	if (WARN_ON_ONCE(!is_guest_mode(vcpu)) ||
> >  		!nested_cpu_has_vid(get_vmcs12(vcpu)) ||
> > -		WARN_ON_ONCE(!vmx->nested.virtual_apic_page))
> > +		WARN_ON_ONCE(!vmx->nested.virtual_apic_map.gfn))
> >  		return false;
> >  
> >  	rvi = vmx_get_rvi();
> >  
> > -	vapic_page = kmap(vmx->nested.virtual_apic_page);
> > +	vapic_page = vmx->nested.virtual_apic_map.hva;
> >  	vppr = *((u32 *)(vapic_page + APIC_PROCPRI));
> > -	kunmap(vmx->nested.virtual_apic_page);
> >  
> >  	return ((rvi & 0xf0) > (vppr & 0xf0));
> >  }
> > diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> > index 6fb69d8..f618f52 100644
> > --- a/arch/x86/kvm/vmx/vmx.h
> > +++ b/arch/x86/kvm/vmx/vmx.h
> > @@ -142,7 +142,7 @@ struct nested_vmx {
> >  	 * pointers, so we must keep them pinned while L2 runs.
> >  	 */
> >  	struct page *apic_access_page;
> > -	struct page *virtual_apic_page;
> > +	struct kvm_host_map virtual_apic_map;
> >  	struct page *pi_desc_page;
> >  
> >  	struct kvm_host_map msr_bitmap_map;
> > -- 
> > 2.7.4
> > 



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