From: Janosch Frank <frankja@linux.ibm.com> To: Claudio Imbrenda <imbrenda@linux.ibm.com>, kvm@vger.kernel.org Cc: cohuck@redhat.com, borntraeger@de.ibm.com, thuth@redhat.com, pasic@linux.ibm.com, david@redhat.com, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 02/13] KVM: s390: pv: leak the ASCE page when destroy fails Date: Thu, 29 Jul 2021 12:41:05 +0200 [thread overview] Message-ID: <21eb4861-f118-cf3b-409e-ea31694582a5@linux.ibm.com> (raw) In-Reply-To: <20210728142631.41860-3-imbrenda@linux.ibm.com> On 7/28/21 4:26 PM, Claudio Imbrenda wrote: > When a protected VM is created, the topmost level of page tables of its > ASCE is marked by the Ultravisor; any attempt to use that memory for > protected virtualization will result in failure. > > Only a successful Destroy Configuration UVC will remove the marking. > > When the Destroy Configuration UVC fails, the topmost level of page > tables of the VM does not get its marking cleared; to avoid issues it > must not be used again. > > Since the page becomes in practice unusable, we set it aside and leak it. > > Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> > --- > arch/s390/kvm/pv.c | 53 +++++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 52 insertions(+), 1 deletion(-) > > diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c > index e007df11a2fe..1ecdc1769ed9 100644 > --- a/arch/s390/kvm/pv.c > +++ b/arch/s390/kvm/pv.c > @@ -155,6 +155,55 @@ static int kvm_s390_pv_alloc_vm(struct kvm *kvm) > return -ENOMEM; > } > > +/* > + * Remove the topmost level of page tables from the list of page tables of > + * the gmap. > + * This means that it will not be freed when the VM is torn down, and needs > + * to be handled separately by the caller, unless an intentional leak is > + * intended. > + */ > +static void kvm_s390_pv_remove_old_asce(struct kvm *kvm) > +{ > + struct page *old; > + > + old = virt_to_page(kvm->arch.gmap->table); > + list_del(&old->lru); > + /* in case the ASCE needs to be "removed" multiple times */ > + INIT_LIST_HEAD(&old->lru); > +} > + > +/* > + * Try to replace the current ASCE with another equivalent one. > + * If the allocation of the new top level page table fails, the ASCE is not > + * replaced. > + * In any case, the old ASCE is removed from the list, therefore the caller > + * has to make sure to save a pointer to it beforehands, unless an > + * intentional leak is intended. > + */ > +static int kvm_s390_pv_replace_asce(struct kvm *kvm) > +{ > + unsigned long asce; > + struct page *page; > + void *table; > + > + kvm_s390_pv_remove_old_asce(kvm); > + > + page = alloc_pages(GFP_KERNEL_ACCOUNT, CRST_ALLOC_ORDER); > + if (!page) > + return -ENOMEM; > + list_add(&page->lru, &kvm->arch.gmap->crst_list); > + > + table = page_to_virt(page); > + memcpy(table, kvm->arch.gmap->table, 1UL << (CRST_ALLOC_ORDER + PAGE_SHIFT)); Don't we want to memcpy first and then add it to the list? The gmap is still active per-se so I think we want to take the guest_table_lock for the list_add here. > + > + asce = (kvm->arch.gmap->asce & ~PAGE_MASK) | __pa(table); > + WRITE_ONCE(kvm->arch.gmap->asce, asce); > + WRITE_ONCE(kvm->mm->context.gmap_asce, asce); > + WRITE_ONCE(kvm->arch.gmap->table, table); If I remember correctly those won't need locks but I'm not 100% sure so please have a look at that. > + > + return 0; > +} That should both be in gmap.c > + > /* this should not fail, but if it does, we must not free the donated memory */ > int kvm_s390_pv_deinit_vm(struct kvm *kvm, u16 *rc, u16 *rrc) > { > @@ -169,9 +218,11 @@ int kvm_s390_pv_deinit_vm(struct kvm *kvm, u16 *rc, u16 *rrc) > atomic_set(&kvm->mm->context.is_protected, 0); > KVM_UV_EVENT(kvm, 3, "PROTVIRT DESTROY VM: rc %x rrc %x", *rc, *rrc); > WARN_ONCE(cc, "protvirt destroy vm failed rc %x rrc %x", *rc, *rrc); > - /* Inteded memory leak on "impossible" error */ > + /* Intended memory leak on "impossible" error */ > if (!cc) > kvm_s390_pv_dealloc_vm(kvm); > + else > + kvm_s390_pv_replace_asce(kvm); > return cc ? -EIO : 0; > } > >
next prev parent reply other threads:[~2021-07-29 10:41 UTC|newest] Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-07-28 14:26 [PATCH v2 00/13] KVM: s390: pv: implement lazy destroy Claudio Imbrenda 2021-07-28 14:26 ` [PATCH v2 01/13] KVM: s390: pv: avoid stall notifications for some UVCs Claudio Imbrenda 2021-07-29 9:58 ` Janosch Frank 2021-07-29 12:52 ` Claudio Imbrenda 2021-07-29 10:49 ` Cornelia Huck 2021-07-29 13:22 ` Claudio Imbrenda 2021-07-28 14:26 ` [PATCH v2 02/13] KVM: s390: pv: leak the ASCE page when destroy fails Claudio Imbrenda 2021-07-29 10:41 ` Janosch Frank [this message] 2021-07-29 12:54 ` Claudio Imbrenda 2021-07-29 13:45 ` Janosch Frank 2021-07-28 14:26 ` [PATCH v2 03/13] KVM: s390: pv: properly handle page flags for protected guests Claudio Imbrenda 2021-07-29 11:43 ` Janosch Frank 2021-07-28 14:26 ` [PATCH v2 04/13] KVM: s390: pv: handle secure storage violations " Claudio Imbrenda 2021-07-28 14:26 ` [PATCH v2 05/13] KVM: s390: pv: handle secure storage exceptions for normal guests Claudio Imbrenda 2021-07-29 12:17 ` Janosch Frank 2021-07-29 13:28 ` Claudio Imbrenda 2021-07-28 14:26 ` [PATCH v2 06/13] KVM: s390: pv: refactor s390_reset_acc Claudio Imbrenda 2021-07-28 14:26 ` [PATCH v2 07/13] KVM: s390: pv: usage counter instead of flag Claudio Imbrenda 2021-07-28 14:26 ` [PATCH v2 08/13] KVM: s390: pv: add export before import Claudio Imbrenda 2021-07-28 14:26 ` [PATCH v2 09/13] KVM: s390: pv: lazy destroy for reboot Claudio Imbrenda 2021-07-28 14:26 ` [PATCH v2 10/13] KVM: s390: pv: extend lazy destroy to handle shutdown Claudio Imbrenda 2021-07-28 14:26 ` [PATCH v2 11/13] KVM: s390: pv: module parameter to fence lazy destroy Claudio Imbrenda 2021-07-28 14:26 ` [PATCH v2 12/13] KVM: s390: pv: add OOM notifier for " Claudio Imbrenda 2021-07-28 14:26 ` [PATCH v2 13/13] KVM: s390: pv: add support for UV feature bits Claudio Imbrenda 2021-07-29 9:52 ` Janosch Frank 2021-07-29 13:28 ` Claudio Imbrenda
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