From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yh0-x230.google.com (mail-yh0-x230.google.com [IPv6:2607:f8b0:4002:c01::230]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id ED24E1A01EF for ; Tue, 29 Jul 2014 18:07:04 +1000 (EST) Received: by mail-yh0-f48.google.com with SMTP id i57so5479865yha.35 for ; Tue, 29 Jul 2014 01:07:02 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1406617022.4935.79.camel@pasglop> References: <1406527744-25316-1-git-send-email-pingfank@linux.vnet.ibm.com> <1406529741.4935.48.camel@pasglop> <1406617022.4935.79.camel@pasglop> Date: Tue, 29 Jul 2014 16:07:01 +0800 Message-ID: Subject: Re: [PATCH] powerpc: kvm: make the setup of hpte under the protection of KVMPPC_RMAP_LOCK_BIT From: Liu ping fan To: Benjamin Herrenschmidt Content-Type: text/plain; charset=UTF-8 Cc: Paul Mackerras , linuxppc-dev@lists.ozlabs.org, Alexander Graf , kvm-ppc List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Jul 29, 2014 at 2:57 PM, Benjamin Herrenschmidt wrote: > On Mon, 2014-07-28 at 15:58 +0800, Liu ping fan wrote: >> Hope I am right. Take the following seq as an example >> >> if (hptep[0] & HPTE_V_VALID) { >> /* HPTE was previously valid, so we need to invalidate it */ >> unlock_rmap(rmap); >> hptep[0] |= HPTE_V_ABSENT; >> kvmppc_invalidate_hpte(kvm, hptep, index); >> /* don't lose previous R and C bits */ >> r |= hptep[1] & (HPTE_R_R | HPTE_R_C); >> } else { >> kvmppc_add_revmap_chain(kvm, rev, rmap, index, 0); >> } >> ---------------------------------------------> if we try_to_unmap on >> pfn at here, then @r contains a invalid pfn >> hptep[1] = r; >> eieio(); >> hptep[0] = hpte[0]; >> asm volatile("ptesync" : : : "memory"); > > If that was the case we would have the same race in kvmppc_do_h_enter(). > > I think the fact that the HPTE is locked will prevent the race, ie, > HPTE_V_HVLOCK is set until hptep[0] is written to. > > If I look at at the unmap case, my understanding is that it uses > kvm_unmap_rmapp() which will also lock the HPTE (try_lock_hpte) > and so shouldn't have a race vs the above code. > Yes, you are right :) Thx, Fan > Or do you see a race I don't ? > > Cheers, > Ben. > >> Thx. >> Fan >> >> On Mon, Jul 28, 2014 at 2:42 PM, Benjamin Herrenschmidt >> wrote: >> > On Mon, 2014-07-28 at 14:09 +0800, Liu Ping Fan wrote: >> >> In current code, the setup of hpte is under the risk of race with >> >> mmu_notifier_invalidate, i.e we may setup a hpte with a invalid pfn. >> >> Resolve this issue by sync the two actions by KVMPPC_RMAP_LOCK_BIT. >> > >> > Please describe the race you think you see. I'm quite sure both Paul and >> > I went over that code and somewhat convinced ourselves that it was ok >> > but it's possible that we were both wrong :-) >> > >> > Cheers, >> > Ben. >> > >> >> Signed-off-by: Liu Ping Fan >> >> --- >> >> arch/powerpc/kvm/book3s_64_mmu_hv.c | 15 ++++++++++----- >> >> 1 file changed, 10 insertions(+), 5 deletions(-) >> >> >> >> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c >> >> index 8056107..e6dcff4 100644 >> >> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c >> >> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c >> >> @@ -754,19 +754,24 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu, >> >> >> >> if (hptep[0] & HPTE_V_VALID) { >> >> /* HPTE was previously valid, so we need to invalidate it */ >> >> - unlock_rmap(rmap); >> >> hptep[0] |= HPTE_V_ABSENT; >> >> kvmppc_invalidate_hpte(kvm, hptep, index); >> >> /* don't lose previous R and C bits */ >> >> r |= hptep[1] & (HPTE_R_R | HPTE_R_C); >> >> + >> >> + hptep[1] = r; >> >> + eieio(); >> >> + hptep[0] = hpte[0]; >> >> + asm volatile("ptesync" : : : "memory"); >> >> + unlock_rmap(rmap); >> >> } else { >> >> + hptep[1] = r; >> >> + eieio(); >> >> + hptep[0] = hpte[0]; >> >> + asm volatile("ptesync" : : : "memory"); >> >> kvmppc_add_revmap_chain(kvm, rev, rmap, index, 0); >> >> } >> >> >> >> - hptep[1] = r; >> >> - eieio(); >> >> - hptep[0] = hpte[0]; >> >> - asm volatile("ptesync" : : : "memory"); >> >> preempt_enable(); >> >> if (page && hpte_is_writable(r)) >> >> SetPageDirty(page); >> > >> > > >