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Thu, 29 Jul 2021 10:41:06 +0000 (GMT) Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3E44A11C07A; Thu, 29 Jul 2021 10:41:06 +0000 (GMT) Received: from localhost.localdomain (unknown [9.145.155.135]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 29 Jul 2021 10:41:06 +0000 (GMT) To: Claudio Imbrenda , 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 References: <20210728142631.41860-1-imbrenda@linux.ibm.com> <20210728142631.41860-3-imbrenda@linux.ibm.com> From: Janosch Frank Subject: Re: [PATCH v2 02/13] KVM: s390: pv: leak the ASCE page when destroy fails Message-ID: <21eb4861-f118-cf3b-409e-ea31694582a5@linux.ibm.com> Date: Thu, 29 Jul 2021 12:41:05 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210728142631.41860-3-imbrenda@linux.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: nKqI9UAJBKnoxS2EC2XuMcvZKomrfjQX X-Proofpoint-ORIG-GUID: xCutagb2i20WU-FQFIbWoRci4TN_OIUn X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-07-29_09:2021-07-29,2021-07-29 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 adultscore=0 priorityscore=1501 impostorscore=0 malwarescore=0 spamscore=0 bulkscore=0 mlxlogscore=999 phishscore=0 lowpriorityscore=0 mlxscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2107290068 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > --- > 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; > } > >