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[79.177.107.202]) by smtp.gmail.com with ESMTPSA id i1sm3843397wrc.49.2020.09.03.03.04.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Sep 2020 03:04:56 -0700 (PDT) Date: Thu, 3 Sep 2020 06:04:54 -0400 From: "Michael S. Tsirkin" To: Ani Sinha Subject: Re: [PATCH] Fix a gap where acpi_pcihp_find_hotplug_bus() returns a non-hotpluggable bus Message-ID: <20200903060332-mutt-send-email-mst@kernel.org> References: <20200829081233.10120-1-ani@anisinha.ca> MIME-Version: 1.0 In-Reply-To: <20200829081233.10120-1-ani@anisinha.ca> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0.003 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=mst@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/03 04:23:49 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_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: Igor Mammedov , jusual@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Sat, Aug 29, 2020 at 01:42:33PM +0530, Ani Sinha wrote: > When ACPI hotplug for the root bus is disabled, the bsel property for that > bus is not set. Please see the following commit: > > 3d7e78aa7777f ("Introduce a new flag for i440fx to disable PCI hotplug on the root bus"). > > As a result, when acpi_pcihp_find_hotplug_bus() is called > with bsel set to 0, it may return the root bus. This would be wrong since the > root bus is not hotpluggable. In general, this can potentially happen to other > buses as well. > In this patch, we fix the issue in this function by checking if the bus returned > by the function is actually hotpluggable. If not, we simply return NULL. This > avoids the scenario where we are actually returning a non-hotpluggable bus. > > Signed-off-by: Ani Sinha What exactly are the consequences though? > --- > hw/acpi/pcihp.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c > index 39b1f74442..f148e73c89 100644 > --- a/hw/acpi/pcihp.c > +++ b/hw/acpi/pcihp.c > @@ -147,6 +147,21 @@ static PCIBus *acpi_pcihp_find_hotplug_bus(AcpiPciHpState *s, int bsel) > if (!bsel && !find.bus) { > find.bus = s->root; > } > + > + /* > + * Check if find.bus is actually hotpluggable. If bsel is set to > + * NULL for example on the root bus in order to make it > + * non-hotpluggable, find.bus will match the root bus when bsel > + * is 0. See acpi_pcihp_test_hotplug_bus() above. Since the > + * bus is not hotpluggable however, we should not select the bus. > + * Instead, we should set find.bus to NULL in that case. In the check > + * below, we generalize this case for all buses, not just the root bus. > + * The callers of this function check for a null return value and > + * handle them appropriately. > + */ > + if (!qbus_is_hotpluggable(BUS(find.bus))) { > + find.bus = NULL; > + } > return find.bus; > } > > -- > 2.17.1