Re: cr3 OOS optimisation breaks 32-bit GNU/kFreeBSD guest

From: Aurelien Jarno <aurelien@aurel32.net>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Avi Kivity <avi@redhat.com>, kvm@vger.kernel.org
Subject: Re: cr3 OOS optimisation breaks 32-bit GNU/kFreeBSD guest
Date: Sun, 5 Apr 2009 01:23:49 +0200	[thread overview]
Message-ID: <20090404232349.GA10658@volta.aurel32.net> (raw)
In-Reply-To: <20090403214548.GA5394@amt.cnet>

On Fri, Apr 03, 2009 at 06:45:48PM -0300, Marcelo Tosatti wrote:
> On Tue, Mar 24, 2009 at 11:47:33AM +0200, Avi Kivity wrote:
> >> index 2ea8262..48169d7 100644
> >> --- a/arch/x86/kvm/x86.c
> >> +++ b/arch/x86/kvm/x86.c
> >> @@ -3109,6 +3109,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
> >>  			kvm_write_guest_time(vcpu);
> >>  		if (test_and_clear_bit(KVM_REQ_MMU_SYNC, &vcpu->requests))
> >>  			kvm_mmu_sync_roots(vcpu);
> >> +		if (test_and_clear_bit(KVM_REQ_MMU_GLOBAL_SYNC, &vcpu->requests))
> >> +			kvm_mmu_sync_global(vcpu);
> >>  		if (test_and_clear_bit(KVM_REQ_TLB_FLUSH, &vcpu->requests))
> >>  			kvm_x86_ops->tlb_flush(vcpu);
> >>  		if (test_and_clear_bit(KVM_REQ_REPORT_TPR_ACCESS
> >
> > Windows will (I think) write a PDE on every context switch, so this  
> > effectively disables global unsync for that guest.
> >
> > What about recursively syncing the newly linked page in FNAME(fetch)()?  
> > If the page isn't global, this becomes a no-op, so no new overhead.  The  
> > only question is the expense when linking a populated top-level page,  
> > especially in long mode.
> 
> How about this?
> 
> KVM: MMU: sync global pages on fetch()
> 
> If an unsync global page becomes unreachable via the shadow tree, which
> can happen if one its parent pages is zapped, invlpg will fail to
> invalidate translations for gvas contained in such unreachable pages.
> 
> So sync global pages in fetch().
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

I have tried this patch, and unfortunately it does not solve the
original problem, while the previous one did.

-- 
Aurelien Jarno	                        GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net