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bh=GdbQ9OqW/5tFe01Vc2vUzlBl29xlYmm13pUFtsgd5+w=; b=cB/+HHi7hf27Mhs+ZRVylddgeLb6QzsvLqCFTxBVcQCQE2EGyuC07Y67Ve5Ih8bzkt2eBE 6+4z8B/3QzCs1IQIyCwdcAf16ygyNVBMnzBMV7yA+V5nL+cWR3JD77PqO0PkvOkjDaO/sY FWE5O2IwIMe4fyFmwwqItUPOzrtD7WI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-497-cSoPcxWuPdShf7zPPtscjQ-1; Wed, 14 Apr 2021 06:49:02 -0400 X-MC-Unique: cSoPcxWuPdShf7zPPtscjQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8F001107ACC7; Wed, 14 Apr 2021 10:49:01 +0000 (UTC) Received: from gondolin (ovpn-113-114.ams2.redhat.com [10.36.113.114]) by smtp.corp.redhat.com (Postfix) with ESMTP id 660D110027C4; Wed, 14 Apr 2021 10:48:56 +0000 (UTC) Date: Wed, 14 Apr 2021 12:48:53 +0200 From: Cornelia Huck To: Ilya Leoshkevich Subject: Re: [PATCH v2] target/s390x: Fix translation exception on illegal instruction Message-ID: <20210414124853.7562f987.cohuck@redhat.com> In-Reply-To: <20210414123936.05f9759a.cohuck@redhat.com> References: <20210413165257.21426-1-iii@linux.ibm.com> <20210414103813.2595508b.cohuck@redhat.com> <9ffa39db0e16efa173119d3b9746bb312e214d87.camel@linux.ibm.com> <710e154736b7e118ae12587a468a8c198cab028c.camel@linux.ibm.com> <20210414123936.05f9759a.cohuck@redhat.com> Organization: Red Hat GmbH MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=cohuck@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=216.205.24.124; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Thomas Huth , David Hildenbrand , Richard Henderson , qemu-devel@nongnu.org, Christian Borntraeger , qemu-s390x@nongnu.org, Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 14 Apr 2021 12:39:36 +0200 Cornelia Huck wrote: > On Wed, 14 Apr 2021 12:27:03 +0200 > Ilya Leoshkevich wrote: >=20 > > On Wed, 2021-04-14 at 11:19 +0200, Ilya Leoshkevich wrote: =20 > > > On Wed, 2021-04-14 at 10:38 +0200, Cornelia Huck wrote: =20 > > > > On Tue, 13 Apr 2021 18:52:57 +0200 > > > > Ilya Leoshkevich wrote: > > > > =20 > > > > > Hitting an uretprobe in a s390x TCG guest causes a SIGSEGV. What > > > > > happens is: > > > > >=20 > > > > > * uretprobe maps a userspace page containing an invalid > > > > > instruction. > > > > > * uretprobe replaces the target function's return address with th= e > > > > > =C2=A0 address of that page. > > > > > * When tb_gen_code() is called on that page, tb->size ends up bei= ng > > > > > 0 > > > > > =C2=A0 (because the page starts with the invalid instruction), wh= ich > > > > > causes > > > > > =C2=A0 virt_page2 to point to the previous page. > > > > > * The previous page is not mapped, so this causes a spurious > > > > > =C2=A0 translation exception. > > > > >=20 > > > > > The bug is that tb->size must never be 0: even if there is an > > > > > illegal > > > > > instruction, the instruction bytes that have been looked at must > > > > > count > > > > > towards tb->size. So adjust s390x's translate_one() to act this w= ay > > > > > for both illegal instructions and instructions that are known to > > > > > generate exceptions. > > > > >=20 > > > > > Also add an assertion to tb_gen_code() in order to detect such > > > > > situations in future. > > > > >=20 > > > > > Signed-off-by: Ilya Leoshkevich > > > > > --- > > > > >=20 > > > > > v1:=20 > > > > > https://lists.nongnu.org/archive/html/qemu-devel/2021-04/msg02037= .html > > > > > v1 -> v2: Fix target/s390x instead of trying to tolerate tb->size > > > > > =3D=3D 0 > > > > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 in tb_gen_= code(). > > > > >=20 > > > > > =C2=A0accel/tcg/translate-all.c |=C2=A0 1 + > > > > > =C2=A0target/s390x/translate.c=C2=A0 | 16 +++++++++++----- > > > > > =C2=A02 files changed, 12 insertions(+), 5 deletions(-) =20 > > > >=20 > > > > I assume this bug is not usually hit during normal usage, right? It= 's > > > > probably not release critical, so I'll line it up for 6.1 instead. = =20 > > >=20 > > > Yes, I saw it only with uprobes, and then it leads only to a process > > > crash, not to a kernel crash. Thanks! =20 > >=20 > > Seems like the new assertion triggers on ARM: > >=20 > > https://gitlab.com/cohuck/qemu/-/jobs/1178409450 =20 >=20 > Yep, I just wanted to make sure it was this patch before complaining :) >=20 > >=20 > > What are the rules in s390x-next-staging, can we amend the patch, or > > only commit a follow-up? =20 >=20 > -staging is before I merge properly, so no problem folding something in. >=20 > > In either case, I think we'll need something > > like this (untested): > >=20 > > --- a/target/arm/translate.c > > +++ b/target/arm/translate.c > > @@ -9060,6 +9060,7 @@ static void > > arm_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu) > > unsigned int insn; > > =20 > > if (arm_pre_translate_insn(dc)) { > > + dc->base.pc_next +=3D 4; > > return; > > } > >=20 > >=20 > > I'm currently trying to debug this in more detail and test the fix. > > =20 >=20 I'm also seeing a problem on xtensa (https://gitlab.com/cohuck/qemu/-/jobs/1178409540), but not sure if it is related to this patch, or more general flakiness.