From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [103.22.144.67]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 2B1361A0225 for ; Mon, 7 Mar 2016 18:30:25 +1100 (AEDT) Date: Mon, 7 Mar 2016 17:00:14 +1100 From: David Gibson To: Alexey Kardashevskiy Cc: linuxppc-dev@lists.ozlabs.org, Paul Mackerras , Alex Williamson , kvm-ppc@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH kernel 3/9] KVM: PPC: Use preregistered memory API to access TCE list Message-ID: <20160307060014.GL22546@voom.fritz.box> References: <1457322077-26640-1-git-send-email-aik@ozlabs.ru> <1457322077-26640-4-git-send-email-aik@ozlabs.ru> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="AQNmCumFClRcGgHG" In-Reply-To: <1457322077-26640-4-git-send-email-aik@ozlabs.ru> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , --AQNmCumFClRcGgHG Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Mar 07, 2016 at 02:41:11PM +1100, Alexey Kardashevskiy wrote: > VFIO on sPAPR already implements guest memory pre-registration > when the entire guest RAM gets pinned. This can be used to translate > the physical address of a guest page containing the TCE list > from H_PUT_TCE_INDIRECT. >=20 > This makes use of the pre-registrered memory API to access TCE list > pages in order to avoid unnecessary locking on the KVM memory > reverse map. >=20 > Signed-off-by: Alexey Kardashevskiy Ok.. so, what's the benefit of not having to lock the rmap? > --- > arch/powerpc/kvm/book3s_64_vio_hv.c | 86 ++++++++++++++++++++++++++++++-= ------ > 1 file changed, 70 insertions(+), 16 deletions(-) >=20 > diff --git a/arch/powerpc/kvm/book3s_64_vio_hv.c b/arch/powerpc/kvm/book3= s_64_vio_hv.c > index 44be73e..af155f6 100644 > --- a/arch/powerpc/kvm/book3s_64_vio_hv.c > +++ b/arch/powerpc/kvm/book3s_64_vio_hv.c > @@ -180,6 +180,38 @@ long kvmppc_gpa_to_ua(struct kvm *kvm, unsigned long= gpa, > EXPORT_SYMBOL_GPL(kvmppc_gpa_to_ua); > =20 > #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE > +static mm_context_t *kvmppc_mm_context(struct kvm_vcpu *vcpu) > +{ > + struct task_struct *task; > + > + task =3D vcpu->arch.run_task; > + if (unlikely(!task || !task->mm)) > + return NULL; > + > + return &task->mm->context; > +} > + > +static inline bool kvmppc_preregistered(struct kvm_vcpu *vcpu) > +{ > + mm_context_t *mm =3D kvmppc_mm_context(vcpu); > + > + if (unlikely(!mm)) > + return false; > + > + return mm_iommu_preregistered(mm); > +} > + > +static struct mm_iommu_table_group_mem_t *kvmppc_rm_iommu_lookup( > + struct kvm_vcpu *vcpu, unsigned long ua, unsigned long size) > +{ > + mm_context_t *mm =3D kvmppc_mm_context(vcpu); > + > + if (unlikely(!mm)) > + return NULL; > + > + return mm_iommu_lookup_rm(mm, ua, size); > +} > + > long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn, > unsigned long ioba, unsigned long tce) > { > @@ -261,23 +293,44 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *= vcpu, > if (ret !=3D H_SUCCESS) > return ret; > =20 > - if (kvmppc_gpa_to_ua(vcpu->kvm, tce_list, &ua, &rmap)) > - return H_TOO_HARD; > + if (kvmppc_preregistered(vcpu)) { > + /* > + * We get here if guest memory was pre-registered which > + * is normally VFIO case and gpa->hpa translation does not > + * depend on hpt. > + */ > + struct mm_iommu_table_group_mem_t *mem; > =20 > - rmap =3D (void *) vmalloc_to_phys(rmap); > + if (kvmppc_gpa_to_ua(vcpu->kvm, tce_list, &ua, NULL)) > + return H_TOO_HARD; > =20 > - /* > - * Synchronize with the MMU notifier callbacks in > - * book3s_64_mmu_hv.c (kvm_unmap_hva_hv etc.). > - * While we have the rmap lock, code running on other CPUs > - * cannot finish unmapping the host real page that backs > - * this guest real page, so we are OK to access the host > - * real page. > - */ > - lock_rmap(rmap); > - if (kvmppc_rm_ua_to_hpa(vcpu, ua, &tces)) { > - ret =3D H_TOO_HARD; > - goto unlock_exit; > + mem =3D kvmppc_rm_iommu_lookup(vcpu, ua, IOMMU_PAGE_SIZE_4K); > + if (!mem || mm_iommu_rm_ua_to_hpa(mem, ua, &tces)) > + return H_TOO_HARD; > + } else { > + /* > + * This is emulated devices case. > + * We do not require memory to be preregistered in this case > + * so lock rmap and do __find_linux_pte_or_hugepte(). > + */ > + if (kvmppc_gpa_to_ua(vcpu->kvm, tce_list, &ua, &rmap)) > + return H_TOO_HARD; > + > + rmap =3D (void *) vmalloc_to_phys(rmap); > + > + /* > + * Synchronize with the MMU notifier callbacks in > + * book3s_64_mmu_hv.c (kvm_unmap_hva_hv etc.). > + * While we have the rmap lock, code running on other CPUs > + * cannot finish unmapping the host real page that backs > + * this guest real page, so we are OK to access the host > + * real page. > + */ > + lock_rmap(rmap); > + if (kvmppc_rm_ua_to_hpa(vcpu, ua, &tces)) { > + ret =3D H_TOO_HARD; > + goto unlock_exit; > + } > } > =20 > for (i =3D 0; i < npages; ++i) { > @@ -291,7 +344,8 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vc= pu, > } > =20 > unlock_exit: > - unlock_rmap(rmap); > + if (rmap) I don't see where rmap is initialized to NULL in the case where it's not being used. > + unlock_rmap(rmap); > =20 > return ret; > } --=20 David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. 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