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Fri, 6 May 2022 11:33:35 +0000 (GMT) Received: from p-imbrenda (unknown [9.145.15.58]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 6 May 2022 11:33:35 +0000 (GMT) Date: Fri, 6 May 2022 13:30:30 +0200 From: Claudio Imbrenda To: Thomas Huth Cc: kvm@vger.kernel.org, borntraeger@de.ibm.com, frankja@linux.ibm.com, pasic@linux.ibm.com, david@redhat.com, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, scgl@linux.ibm.com, mimu@linux.ibm.com, nrb@linux.ibm.com Subject: Re: [PATCH v10 01/19] KVM: s390: pv: leak the topmost page table when destroy fails Message-ID: <20220506133030.6b51e019@p-imbrenda> In-Reply-To: <08f78cc7-b34e-cdca-72b8-a0f9163f3ca7@redhat.com> References: <20220414080311.1084834-1-imbrenda@linux.ibm.com> <20220414080311.1084834-2-imbrenda@linux.ibm.com> <08f78cc7-b34e-cdca-72b8-a0f9163f3ca7@redhat.com> Organization: IBM X-Mailer: Claws Mail 3.18.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 3lUAbrIdoCp1ZFtq-KSKYH0w0qDcRcST X-Proofpoint-GUID: Y3dkZDtvUpBcPzuwHcIGWPRBf7ttbErd X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.858,Hydra:6.0.486,FMLib:17.11.64.514 definitions=2022-05-06_04,2022-05-06_01,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 priorityscore=1501 adultscore=0 clxscore=1015 mlxlogscore=999 impostorscore=0 mlxscore=0 lowpriorityscore=0 bulkscore=0 suspectscore=0 malwarescore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2202240000 definitions=main-2205060064 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 5 May 2022 16:45:13 +0200 Thomas Huth wrote: > On 14/04/2022 10.02, Claudio Imbrenda wrote: > > Each secure guest must have a unique ASCE (address space control > > element); we must avoid that new guests use the same page for their > > ASCE, to avoid errors. > > > > Since the ASCE mostly consists of the address of the topmost page table > > (plus some flags), we must not return that memory to the pool unless > > the ASCE is no longer in use. > > > > Only a successful Destroy Secure Configuration UVC will make the ASCE > > reusable again. > > > > If the Destroy Configuration UVC fails, the ASCE cannot be reused for a > > secure guest (either for the ASCE or for other memory areas). To avoid > > a collision, it must not be used again. This is a permanent error and > > the page becomes in practice unusable, so we set it aside and leak it. > > On failure we already leak other memory that belongs to the ultravisor > > (i.e. the variable and base storage for a guest) and not leaking the > > topmost page table was an oversight. > > > > This error (and thus the leakage) should not happen unless the hardware > > is broken or KVM has some unknown serious bug. > > > > Signed-off-by: Claudio Imbrenda > > Fixes: 29b40f105ec8d55 ("KVM: s390: protvirt: Add initial vm and cpu lifecycle handling") > > --- > > arch/s390/include/asm/gmap.h | 2 + > > arch/s390/kvm/pv.c | 9 ++-- > > arch/s390/mm/gmap.c | 80 ++++++++++++++++++++++++++++++++++++ > > 3 files changed, 88 insertions(+), 3 deletions(-) > > > > diff --git a/arch/s390/include/asm/gmap.h b/arch/s390/include/asm/gmap.h > > index 40264f60b0da..746e18bf8984 100644 > > --- a/arch/s390/include/asm/gmap.h > > +++ b/arch/s390/include/asm/gmap.h > > @@ -148,4 +148,6 @@ void gmap_sync_dirty_log_pmd(struct gmap *gmap, unsigned long dirty_bitmap[4], > > unsigned long gaddr, unsigned long vmaddr); > > int gmap_mark_unmergeable(void); > > void s390_reset_acc(struct mm_struct *mm); > > +void s390_remove_old_asce(struct gmap *gmap); > > +int s390_replace_asce(struct gmap *gmap); > > #endif /* _ASM_S390_GMAP_H */ > > diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c > > index 7f7c0d6af2ce..3c59ef763dde 100644 > > --- a/arch/s390/kvm/pv.c > > +++ b/arch/s390/kvm/pv.c > > @@ -166,10 +166,13 @@ 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 */ > > - if (!cc) > > + /* Intended memory leak on "impossible" error */ > > + if (!cc) { > > kvm_s390_pv_dealloc_vm(kvm); > > - return cc ? -EIO : 0; > > + return 0; > > + } > > + s390_replace_asce(kvm->arch.gmap); > > + return -EIO; > > } > > > > int kvm_s390_pv_init_vm(struct kvm *kvm, u16 *rc, u16 *rrc) > > diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c > > index af03cacf34ec..e8904cb9dc38 100644 > > --- a/arch/s390/mm/gmap.c > > +++ b/arch/s390/mm/gmap.c > > @@ -2714,3 +2714,83 @@ void s390_reset_acc(struct mm_struct *mm) > > mmput(mm); > > } > > EXPORT_SYMBOL_GPL(s390_reset_acc); > > + > > +/** > > + * s390_remove_old_asce - Remove the topmost level of page tables from the > > + * list of page tables of the gmap. > > + * @gmap the gmap whose table is to be removed > > + * > > + * 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. Notice that this function will only remove the page from the > > "intentional leak is intended" ... sounds redundant. Scratch the first > "intentional" ? > > > + * list, the page will still be used as a top level page table (and ASCE). > > + */ > > +void s390_remove_old_asce(struct gmap *gmap) > > +{ > > + struct page *old; > > + > > + old = virt_to_page(gmap->table); > > + spin_lock(&gmap->guest_table_lock); > > + list_del(&old->lru); > > + /* > > + * In case the ASCE needs to be "removed" multiple times, for example > > + * if the VM is rebooted into secure mode several times > > + * concurrently, or if s390_replace_asce fails after calling > > + * s390_remove_old_asce and is attempted again later. In that case > > "In case the ASCE ... . In that case" - this should be either one big > sentence, or better, scratch the first "In case" and use "Sometimes" or > something similar to start the first sentence. > > > + * the old asce has been removed from the list, and therefore it > > + * will not be freed when the VM terminates, but the ASCE is still > > + * in use and still pointed to. > > + * A subsequent call to replace_asce will follow the pointer and try > > + * to remove the same page from the list again. > > + * Therefore it's necessary that the page of the ASCE has valid > > + * pointers, so list_del can work (and do nothing) without > > + * dereferencing stale or invalid pointers. > > + */ > > + INIT_LIST_HEAD(&old->lru); > > + spin_unlock(&gmap->guest_table_lock); > > +} > > +EXPORT_SYMBOL_GPL(s390_remove_old_asce); > > + > > +/** > > + * s390_replace_asce - Try to replace the current ASCE of a gmap with > > + * another equivalent one. > > + * @gmap the gmap > > "the gmap" is not a very helpful description for a parmeter that is already > called gmap. Write at least "the guest map that should be replaced" ? > > > + * > > + * If the allocation of the new top level page table fails, the ASCE is not > > + * replaced. > > + * In any case, the old ASCE is always removed from the list. Therefore the > > + * caller has to make sure to save a pointer to it beforehands, unless an > > s/beforehands/beforehand/ > > > + * intentional leak is intended. > > scratch "intentional". > > > + */ > > +int s390_replace_asce(struct gmap *gmap) > > +{ > > + unsigned long asce; > > + struct page *page; > > + void *table; > > + > > + s390_remove_old_asce(gmap); > > + > > + page = alloc_pages(GFP_KERNEL_ACCOUNT, CRST_ALLOC_ORDER); > > + if (!page) > > + return -ENOMEM; > > + table = page_to_virt(page); > > + memcpy(table, gmap->table, 1UL << (CRST_ALLOC_ORDER + PAGE_SHIFT)); > > + > > + /* > > + * The caller has to deal with the old ASCE, but here we make sure > > + * the new one is properly added to the list of page tables, so that > > + * it will be freed when the VM is torn down. > > + */ > > + spin_lock(&gmap->guest_table_lock); > > + list_add(&page->lru, &gmap->crst_list); > > + spin_unlock(&gmap->guest_table_lock); > > + > > + /* Set new table origin while preserving existing ASCE control bits */ > > + asce = (gmap->asce & ~_ASCE_ORIGIN) | __pa(table); > > + WRITE_ONCE(gmap->asce, asce); > > + WRITE_ONCE(gmap->mm->context.gmap_asce, asce); > > + WRITE_ONCE(gmap->table, table); > > + > > + return 0; > > +} > > +EXPORT_SYMBOL_GPL(s390_replace_asce); > > Thomas > thanks, I will fix them all