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Tsirkin" To: Igor Mammedov Subject: Re: [PATCH 2/4] pcie: update slot power status only is power control is enabled Message-ID: <20220225044907-mutt-send-email-mst@kernel.org> References: <20220224174411.3296848-1-imammedo@redhat.com> <20220224174411.3296848-3-imammedo@redhat.com> <20220224125928-mutt-send-email-mst@kernel.org> <20220225091830.2f684997@redhat.com> MIME-Version: 1.0 In-Reply-To: <20220225091830.2f684997@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, 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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, kraxel@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Feb 25, 2022 at 09:18:30AM +0100, Igor Mammedov wrote: > On Thu, 24 Feb 2022 13:05:07 -0500 > "Michael S. Tsirkin" wrote: > > > On Thu, Feb 24, 2022 at 12:44:09PM -0500, Igor Mammedov wrote: > > > on creation a PCIDevice has power turned on at the end of pci_qdev_realize() > > > however later on if PCIe slot isn't populated with any children > > > it's power is turned off. It's fine if native hotplug is used > > > as plug callback will power slot on among other things. > > > However when ACPI hotplug is enabled it replaces native PCIe plug > > > callbacks with ACPI specific ones (acpi_pcihp_device_*plug_cb) and > > > as result slot stays powered off. It works fine as ACPI hotplug > > > on guest side takes care of enumerating/initializing hotplugged > > > device. But when later guest is migrated, call chain introduced by [1] > > > > > > pcie_cap_slot_post_load() > > > -> pcie_cap_update_power() > > > -> pcie_set_power_device() > > > -> pci_set_power() > > > -> pci_update_mappings() > > > > > > will disable earlier initialized BARs for the hotplugged device > > > in powered off slot due to commit [2] which disables BARs if > > > power is off. As result guest OS after migration will be very > > > much confused [3], still thinking that it has working device, > > > which isn't true anymore due to disabled BARs. > > > > > > Fix it by honoring PCI_EXP_SLTCAP_PCP and updating power status > > > only if capability is enabled. Follow up patch will disable > > > PCI_EXP_SLTCAP_PCP overriding COMPAT_PROP_PCP property when > > > PCIe slot is under ACPI PCI hotplug control. > > > > > > See [3] for reproducer. > > > > > > 1) > > > Fixes: commit d5daff7d312 (pcie: implement slot power control for pcie root ports) > > > 2) > > > commit 23786d13441 (pci: implement power state) > > > 3) > > > Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2053584 > > > > > > > > > Correct format for the last paragraph: > > > > > > Fixes: d5daff7d312 ("pcie: implement slot power control for pcie root ports") > > Fixes: 23786d13441 ("pci: implement power state") > > Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2053584 > > ok, will fix it up on respin like this to have references: > > 1) > Fixes: d5daff7d312 ("pcie: implement slot power control for pcie root ports") > 2) > Fixes: 23786d13441 ("pci: implement power state") > Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2053584 Just drop references, a bit of duplication is not a problem. E.g. in powered off slot due to commit 23786d13441 ("pci: implement power state") which disables BARs if Trailer tags belong in a group at the end with no interruptions, not all tools handle them otherwise. > > > > > Signed-off-by: Igor Mammedov > > > --- > > > hw/pci/pcie.c | 5 ++--- > > > 1 file changed, 2 insertions(+), 3 deletions(-) > > > > > > diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c > > > index d7d73a31e4..2339729a7c 100644 > > > --- a/hw/pci/pcie.c > > > +++ b/hw/pci/pcie.c > > > @@ -383,10 +383,9 @@ static void pcie_cap_update_power(PCIDevice *hotplug_dev) > > > > > > if (sltcap & PCI_EXP_SLTCAP_PCP) { > > > power = (sltctl & PCI_EXP_SLTCTL_PCC) == PCI_EXP_SLTCTL_PWR_ON; > > > + pci_for_each_device(sec_bus, pci_bus_num(sec_bus), > > > + pcie_set_power_device, &power); > > > } > > > - > > > - pci_for_each_device(sec_bus, pci_bus_num(sec_bus), > > > - pcie_set_power_device, &power); > > > > I think this is correct. However, I wonder whether for 6.2 compatiblity > > as a hack we should sometimes skip the power update even when > > PCI_EXP_SLTCAP_PCP exists. Will that not work around the issue for > > these machine types? > > pc-q35-6.2 is broken utterly. > With pc-q35-6.1, it's a mess. Here is a ping-pong migration matrix for it > > v6.1 | v6.2 | Fix > v6.1 ok | broken | ok (#1) > v6.2 | broken | broken (#2) > > [1] has PCI_EXP_SLTCAP_PCP due to x-pcihp-enable-pcie-pcp-cap=on > i.e. pci_config is exactly the same as in qemu-v6.1 > [2] PCI_EXP_SLTCAP_PCP is enabled + empty slot is powered off > (+ state is migrated) > > there are some invariants that might work in one direction, > but it won't survive ping-pong migration. And more importantly > for upstream we care mostly care for old -> new working, > and it's direction that is broken in v6.2. > > > And assuming we want bug for bug compat anyway, why not just put > > it here? It seems easier to reason about frankly ... > > It should be possible hack PCI core to fixup broken power state > on incoming migration at (at postload time), but that would just > create more confusion, where in some cases migration would work > and in some would not (depending on used qemu versions). > > Lets just declare v6.2 qemu broken, with upgrade/downgrade to > (7.0/6.1) as suggested solution. > > PS: > I'd very much prefer avoid adding hacks for ACPI pcihp sake to > PCI core, and let PCI code behave as it's supposed to per spec. > It's already bad enough with pcihp layered on top of PCI, > making PCI code depend on pcihp will just make it more fragile. > > > > } > > > > > > /* > > > -- > > > 2.31.1 > >