Path: csiph.com!news.redatomik.org!aioe.org!bofh.it!news.nic.it!robomod From: Greg Kroah-Hartman Newsgroups: linux.kernel Subject: [PATCH 4.4 31/35] KVM: s390: Fix guest migration for huge guests resulting in panic Date: Thu, 16 Mar 2017 16:10:02 +0100 Message-ID: References: X-Original-To: linux-kernel@vger.kernel.org X-Mailer: git-send-email 2.12.0 User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 61 Organization: linux.* mail to news gateway X-Original-Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Janosch Frank , Christian Borntraeger , Martin Schwidefsky X-Original-Date: Thu, 16 Mar 2017 23:29:50 +0900 X-Original-Message-ID: <20170316142908.779801273@linuxfoundation.org> X-Original-References: <20170316142906.685052998@linuxfoundation.org> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1602458 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Janosch Frank commit 2e4d88009f57057df7672fa69a32b5224af54d37 upstream. While we can technically not run huge page guests right now, we can setup a guest with huge pages. Trying to migrate it will trigger a VM_BUG_ON and, if the kernel is not configured to panic on a BUG, it will happily try to work on non-existing page table entries. With this patch, we always return "dirty" if we encounter a large page when migrating. This at least fixes the immediate problem until we have proper handling for both kind of pages. Fixes: 15f36eb ("KVM: s390: Add proper dirty bitmap support to S390 kvm.") Cc: # 3.16+ Signed-off-by: Janosch Frank Acked-by: Christian Borntraeger Signed-off-by: Martin Schwidefsky Signed-off-by: Greg Kroah-Hartman --- arch/s390/mm/pgtable.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) --- a/arch/s390/mm/pgtable.c +++ b/arch/s390/mm/pgtable.c @@ -1237,11 +1237,28 @@ EXPORT_SYMBOL_GPL(s390_reset_cmma); */ bool gmap_test_and_clear_dirty(unsigned long address, struct gmap *gmap) { + pgd_t *pgd; + pud_t *pud; + pmd_t *pmd; pte_t *pte; spinlock_t *ptl; bool dirty = false; - pte = get_locked_pte(gmap->mm, address, &ptl); + pgd = pgd_offset(gmap->mm, address); + pud = pud_alloc(gmap->mm, pgd, address); + if (!pud) + return false; + pmd = pmd_alloc(gmap->mm, pud, address); + if (!pmd) + return false; + /* We can't run guests backed by huge pages, but userspace can + * still set them up and then try to migrate them without any + * migration support. + */ + if (pmd_large(*pmd)) + return true; + + pte = pte_alloc_map_lock(gmap->mm, pmd, address, &ptl); if (unlikely(!pte)) return false;