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Tue, 6 Oct 2020 18:58:28 +0200 Authentication-Results: garm.ovh; auth=pass (GARM-97G00210abf313-f72d-4754-b904-eaf0e3db91d1, ABBA5CC1B3A583228A496F54FDB0659883642288) smtp.auth=groug@kaod.org Date: Tue, 6 Oct 2020 18:58:26 +0200 From: Greg Kurz To: =?UTF-8?B?Q8OpZHJpYw==?= Le Goater Subject: Re: [PATCH v2 3/6] spapr/xive: Add a warning when StoreEOI is activated on POWER9 CPUs Message-ID: <20201006185826.65f8ff3b@bahia.lan> In-Reply-To: <20201005165147.526426-4-clg@kaod.org> References: <20201005165147.526426-1-clg@kaod.org> <20201005165147.526426-4-clg@kaod.org> X-Mailer: Claws Mail 3.17.6 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Originating-IP: [37.59.142.97] X-ClientProxiedBy: DAG6EX2.mxp5.local (172.16.2.52) To DAG8EX1.mxp5.local (172.16.2.71) X-Ovh-Tracer-GUID: 67ba1b69-7e6c-4dfb-9164-a12ca0454db4 X-Ovh-Tracer-Id: 11687966937152264611 X-VR-SPAMSTATE: OK X-VR-SPAMSCORE: -100 X-VR-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrgedujedrgeeggddutdeiucetufdoteggodetrfdotffvucfrrhhofhhilhgvmecuqfggjfdpvefjgfevmfevgfenuceurghilhhouhhtmecuhedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujfgurhepfffhvffukfgjfhfogggtgfhisehtqhertdertdejnecuhfhrohhmpefirhgvghcumfhurhiiuceoghhrohhugheskhgrohgurdhorhhgqeenucggtffrrghtthgvrhhnpeevlefhtddufffhieevhefhleegleelgfetffetkedugeehjeffgfehhfefueduffenucfkpheptddrtddrtddrtddpfeejrdehledrudegvddrleejnecuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmohguvgepshhmthhpqdhouhhtpdhhvghlohepmhigphhlrghnhedrmhgrihhlrdhovhhhrdhnvghtpdhinhgvtheptddrtddrtddrtddpmhgrihhlfhhrohhmpehgrhhouhhgsehkrghougdrohhrghdprhgtphhtthhopegtlhhgsehkrghougdrohhrgh Received-SPF: pass client-ip=178.32.125.2; envelope-from=groug@kaod.org; helo=smtpout1.mo529.mail-out.ovh.net X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/06 12:58:29 X-ACL-Warn: Detected OS = Linux 3.11 and newer X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-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: Gustavo Romero , qemu-ppc@nongnu.org, qemu-devel@nongnu.org, David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, 5 Oct 2020 18:51:44 +0200 C=C3=A9dric Le Goater wrote: > StoreEOI on POWER9 CPUs is racy because load-after-store ordering is > not enforced. >=20 > Signed-off-by: C=C3=A9dric Le Goater > --- > hw/ppc/spapr_caps.c | 9 +++++++++ > 1 file changed, 9 insertions(+) >=20 > diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c > index b0a9d0227db2..9251badbdc27 100644 > --- a/hw/ppc/spapr_caps.c > +++ b/hw/ppc/spapr_caps.c > @@ -549,6 +549,15 @@ static void cap_storeeoi_apply(SpaprMachineState *sp= apr, uint8_t val, > error_setg(errp, "StoreEOI not supported by KVM"); > return; > } > + > + /* > + * load-after-store ordering is not enforced on POWER9 CPUs > + * and StoreEOI can be racy. > + */ > + if (!ppc_type_check_compat(machine->cpu_type, CPU_POWERPC_LOGICA= L_3_10, > + 0, spapr->max_compat_pvr)) { > + warn_report("StoreEOI on a POWER9 CPU is unsafe on KVM."); It all boils down to what "unsafe" really means here... if the outcome is "very likely hang the guest" as soon as it starts doing I/O, shouldn't we error out instead ? What is the motivation to use StoreEOI if the processor doesn't really support it ? > + } > } > } > =20