linux-kernel - Re: [PATCH v6 09/12] Inject asynchronous page fault into a PV guest if page is swapped out.

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Message-ID: <20101006104259.GT11145@redhat.com>
Date:	Wed, 6 Oct 2010 12:42:59 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	kvm@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, avi@...hat.com, mingo@...e.hu,
	a.p.zijlstra@...llo.nl, tglx@...utronix.de, hpa@...or.com,
	riel@...hat.com, cl@...ux-foundation.org
Subject: Re: [PATCH v6 09/12] Inject asynchronous page fault into a PV
 guest if page is swapped out.

On Tue, Oct 05, 2010 at 04:00:51PM -0300, Marcelo Tosatti wrote:
> On Mon, Oct 04, 2010 at 05:56:31PM +0200, Gleb Natapov wrote:
> > Send async page fault to a PV guest if it accesses swapped out memory.
> > Guest will choose another task to run upon receiving the fault.
> > 
> > Allow async page fault injection only when guest is in user mode since
> > otherwise guest may be in non-sleepable context and will not be able
> > to reschedule.
> > 
> > Vcpu will be halted if guest will fault on the same page again or if
> > vcpu executes kernel code.
> > 
> > Signed-off-by: Gleb Natapov <gleb@...hat.com>
> > ---
> >  arch/x86/include/asm/kvm_host.h |    3 ++
> >  arch/x86/kvm/mmu.c              |    1 +
> >  arch/x86/kvm/x86.c              |   49 ++++++++++++++++++++++++++++++++------
> >  include/trace/events/kvm.h      |   17 ++++++++----
> >  virt/kvm/async_pf.c             |    3 +-
> >  5 files changed, 58 insertions(+), 15 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index de31551..2f6fc87 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -419,6 +419,7 @@ struct kvm_vcpu_arch {
> >  		gfn_t gfns[roundup_pow_of_two(ASYNC_PF_PER_VCPU)];
> >  		struct gfn_to_hva_cache data;
> >  		u64 msr_val;
> > +		u32 id;
> >  	} apf;
> >  };
> >  
> > @@ -594,6 +595,7 @@ struct kvm_x86_ops {
> >  };
> >  
> >  struct kvm_arch_async_pf {
> > +	u32 token;
> >  	gfn_t gfn;
> >  };
> >  
> > @@ -842,6 +844,7 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
> >  				 struct kvm_async_pf *work);
> >  void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu,
> >  			       struct kvm_async_pf *work);
> > +bool kvm_arch_can_inject_async_page_present(struct kvm_vcpu *vcpu);
> >  extern bool kvm_find_async_pf_gfn(struct kvm_vcpu *vcpu, gfn_t gfn);
> >  
> >  #endif /* _ASM_X86_KVM_HOST_H */
> > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> > index d85fda8..de53cab 100644
> > --- a/arch/x86/kvm/mmu.c
> > +++ b/arch/x86/kvm/mmu.c
> > @@ -2580,6 +2580,7 @@ static int nonpaging_page_fault(struct kvm_vcpu *vcpu, gva_t gva,
> >  int kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn)
> >  {
> >  	struct kvm_arch_async_pf arch;
> > +	arch.token = (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id;
> >  	arch.gfn = gfn;
> >  
> >  	return kvm_setup_async_pf(vcpu, gva, gfn, &arch);
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 3e123ab..0e69d37 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -6225,25 +6225,58 @@ static void kvm_del_async_pf_gfn(struct kvm_vcpu *vcpu, gfn_t gfn)
> >  	}
> >  }
> >  
> > +static int apf_put_user(struct kvm_vcpu *vcpu, u32 val)
> > +{
> > +
> > +	return kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.apf.data, &val,
> > +				      sizeof(val));
> > +}
> > +
> >  void kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu,
> >  				     struct kvm_async_pf *work)
> >  {
> > -	vcpu->arch.mp_state = KVM_MP_STATE_HALTED;
> > -
> > -	if (work == kvm_double_apf)
> > +	if (work == kvm_double_apf) {
> >  		trace_kvm_async_pf_doublefault(kvm_rip_read(vcpu));
> > -	else {
> > -		trace_kvm_async_pf_not_present(work->gva);
> > -
> > +		vcpu->arch.mp_state = KVM_MP_STATE_HALTED;
> > +	} else {
> > +		trace_kvm_async_pf_not_present(work->arch.token, work->gva);
> >  		kvm_add_async_pf_gfn(vcpu, work->arch.gfn);
> > +
> > +		if (!(vcpu->arch.apf.msr_val & KVM_ASYNC_PF_ENABLED) ||
> > +		    kvm_x86_ops->get_cpl(vcpu) == 0)
> > +			vcpu->arch.mp_state = KVM_MP_STATE_HALTED;
> > +		else if (!apf_put_user(vcpu, KVM_PV_REASON_PAGE_NOT_PRESENT)) {
> > +			vcpu->arch.fault.error_code = 0;
> > +			vcpu->arch.fault.address = work->arch.token;
> > +			kvm_inject_page_fault(vcpu);
> > +		}
> 
> Missed !kvm_event_needs_reinjection(vcpu) ? 
This check is done in can_do_async_pf(). We will not get here if event is pending.

--
			Gleb.
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