From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38126) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eFOL3-00022v-Rw for qemu-devel@nongnu.org; Thu, 16 Nov 2017 12:52:34 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eFOL0-0003QB-MO for qemu-devel@nongnu.org; Thu, 16 Nov 2017 12:52:33 -0500 References: <20171116170526.12643-1-david@redhat.com> <20171116170526.12643-3-david@redhat.com> <87375e15vx.fsf@linaro.org> From: David Hildenbrand Message-ID: Date: Thu, 16 Nov 2017 18:52:26 +0100 MIME-Version: 1.0 In-Reply-To: <87375e15vx.fsf@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v1 for-2.11 2/3] s390x/tcg: fix DIAG 308 with > 1 VCPU (single threaded TCG) List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?UTF-8?Q?Alex_Benn=c3=a9e?= Cc: qemu-s390x@nongnu.org, qemu-devel@nongnu.org, Christian Borntraeger , Cornelia Huck , Alexander Graf , Richard Henderson On 16.11.2017 18:37, Alex Benn=C3=A9e wrote: >=20 > David Hildenbrand writes: >=20 >> Currently, single threaded TCG with > 1 VCPU gets stuck during IPL, wh= en >> the bios tries to switch to the loaded kernel via DIAG 308. >> >> pause_all_vcpus()/resume_all_vcpus() should not be called from a VCPU. >> >> And there is also no need for it. run_on_cpu() will make sure that the >> CPUs exit KVM/TCG, where they get stopped. Once stopped, they will no >> longer run. >> >> Signed-off-by: David Hildenbrand >> --- >> target/s390x/diag.c | 4 ---- >> 1 file changed, 4 deletions(-) >> >> diff --git a/target/s390x/diag.c b/target/s390x/diag.c >> index dbbb9e886f..52bc348808 100644 >> --- a/target/s390x/diag.c >> +++ b/target/s390x/diag.c >> @@ -27,7 +27,6 @@ static int modified_clear_reset(S390CPU *cpu) >> S390CPUClass *scc =3D S390_CPU_GET_CLASS(cpu); >> CPUState *t; >> >> - pause_all_vcpus(); >> cpu_synchronize_all_states(); >> CPU_FOREACH(t) { >> run_on_cpu(t, s390_do_cpu_full_reset, RUN_ON_CPU_NULL); >=20 > I think you also need to fix the run_on_cpu to be a async_run_on_cpu as > you would otherwise hang waiting for run_on_cpu to finish on a > single-threaded TCG run (as you are in the only vCPU context). No, it works just fine for single threaded TCG. run_on_cpu() can deal with single threaded TCG just fine. (otherwise e.g. SIGP code also wouldn't work) In do_run_on_cpu, the following code always directly triggers for single threaded tcg: if (qemu_cpu_is_self(cpu)) { func(cpu, data); return; } >=20 > If it is important that the source vCPU doesn't continue you can > schedule it's work afterwards with a async_safe_run_on_cpu which will > complete after all other vCPUs have executed their work. >=20 It is important. Introducing async helpers at a point where sync is needed sounds strange. Thanks! >> >> -- >> 2.13.6 >=20 >=20 > -- > Alex Benn=C3=A9e >=20 --=20 Thanks, David / dhildenb