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Tsirkin" To: Leonardo =?iso-8859-1?Q?Br=E1s?= Cc: Peter Xu , Marcel Apfelbaum , Juan Quintela , qemu-devel@nongnu.org, Julia Suvorova , Igor Mammedov , David Gibson Subject: Re: [PATCH 1/1] pcie: Add hotplug detect state register to w1cmask Message-ID: <20230704024051-mutt-send-email-mst@kernel.org> References: <20230629090500.438976-2-leobras@redhat.com> <20230629152644-mutt-send-email-mst@kernel.org> <20230629160643-mutt-send-email-mst@kernel.org> <2364a62d0cc278c43dd19da4aceeee70513990e1.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <2364a62d0cc278c43dd19da4aceeee70513990e1.camel@redhat.com> 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: -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_H4=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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Jul 04, 2023 at 03:20:36AM -0300, Leonardo Brás wrote: > Hello Peter and Michael, I have a few updates on this: > > On Mon, 2023-07-03 at 02:20 -0300, Leonardo Brás wrote: > > Hello Peter and Michael, thanks for reviewing! > > > > > > On Thu, 2023-06-29 at 16:56 -0400, Peter Xu wrote: > > > On Thu, Jun 29, 2023 at 04:06:53PM -0400, Michael S. Tsirkin wrote: > > > > On Thu, Jun 29, 2023 at 04:01:41PM -0400, Peter Xu wrote: > > > > > On Thu, Jun 29, 2023 at 03:33:06PM -0400, Michael S. Tsirkin wrote: > > > > > > On Thu, Jun 29, 2023 at 01:01:53PM -0400, Peter Xu wrote: > > > > > > > Hi, Leo, > > > > > > > > > > > > > > Thanks for figuring this out. Let me copy a few more potential reviewers > > > > > > > from commit 17858a1695 ("hw/acpi/ich9: Set ACPI PCI hot-plug as default on > > > > > > > Q35"). > > > > > > > > > > > > > > On Thu, Jun 29, 2023 at 06:05:00AM -0300, Leonardo Bras wrote: > > > > > > > > When trying to migrate a machine type pc-q35-6.0 or lower, with this > > > > > > > > cmdline options: > > > > > > > > > > > > > > > > -device driver=pcie-root-port,port=18,chassis=19,id=pcie-root-port18,bus=pcie.0,addr=0x12 \ > > > > > > > > -device driver=nec-usb-xhci,p2=4,p3=4,id=nex-usb-xhci0,bus=pcie-root-port18,addr=0x12.0x1 > > > > > > > > > > > > > > > > the following bug happens after all ram pages were sent: > > > > > > > > > > > > > > > > qemu-kvm: get_pci_config_device: Bad config data: i=0x6e read: 0 device: 40 cmask: ff wmask: 0 w1cmask:19 > > > > > > > > qemu-kvm: Failed to load PCIDevice:config > > > > > > > > qemu-kvm: Failed to load pcie-root-port:parent_obj.parent_obj.parent_obj > > > > > > > > qemu-kvm: error while loading state for instance 0x0 of device '0000:00:12.0/pcie-root-port' > > > > > > > > qemu-kvm: load of migration failed: Invalid argument > > > > > > > > > > > > > > > > This happens on pc-q35-6.0 or lower because of: > > > > > > > > { "ICH9-LPC", ACPI_PM_PROP_ACPI_PCIHP_BRIDGE, "off" } > > > > > > > > > > > > > > > > In this scenario, hotplug_handler_plug() calls pcie_cap_slot_plug_cb(), > > > > > > > > which sets the bus dev->config byte 0x6e with bit PCI_EXP_SLTSTA_PDS to > > > > > > > > signal PCI hotplug for the guest. After a while the guest will deal with > > > > > > > > this hotplug and qemu will clear the above bit. > > > > > > > > > > > > Presence Detect State – This bit indicates the presence of an > > > > > > adapter in the slot, reflected by the logical “OR” of the Physical > > > > > > Layer in-band presence detect mechanism and, if present, any > > > > > > out-of-band presence detect mechanism defined for the slot’s > > > > > > corresponding form factor. Note that the in-band presence > > > > > > detect mechanism requires that power be applied to an adapter > > > > > > for its presence to be detected. Consequently, form factors that > > > > > > require a power controller for hot-plug must implement a > > > > > > physical pin presence detect mechanism. > > > > > > RO > > > > > > Defined encodings are: > > > > > > 0b Slot Empty > > > > > > 1b Card Present in slot > > > > > > This bit must be implemented on all Downstream Ports that > > > > > > implement slots. For Downstream Ports not connected to slots > > > > > > (where the Slot Implemented bit of the PCI Express Capabilities > > > > > > register is 0b), this bit must be hardwired to 1b. > > > > Thank you for providing this doc! > > I am new to PCI stuff, could you please point this doc? > > (I mean, the link to the documentation) The pci specs are all here: https://pcisig.com/ Red Hat is a member so just register, it's free. I'd get the 5.0 version of pci express base: https://members.pcisig.com/wg/PCI-SIG/document/13005 6.0 is out but they did something to make it take years to open, and it shouldn't matter for this. > > > > > > > > > > > > > > > > > > > > And this seems to match what QEMU is doing: it clears on unplug > > > > > > not after guest deals with hotplug. > > > > Oh, that's weird. > > It should not unplug the device, so IIUC it should not clear the bit. > > Maybe something weird is happening in the guest, I will take a look. > > Updates on this: > You are right! For some reason the guest is hot-unplugging the device under some > conditions, so there is another bug on this for me to look after. > > > > > > > > > > > > > > > > > > > > > > > Then, during migration, get_pci_config_device() will compare the > > > > > > > > configs of both the freshly created device and the one that is being > > > > > > > > received via migration, which will differ due to the PCI_EXP_SLTSTA_PDS bit > > > > > > > > and cause the bug to reproduce. > > > > > > > > > > > > So bit is set on source. > > > > > > But why is the bit cleared on destination? This is the part I don't get. > > > > No, bit is set when the device is created by qemu. > > After some time running (boot process completion) the bit is cleared. > > The 'after some time' here is about the guest hot-unplugging the device. > > > > > The receiving end of migration will then create the device with the bit set, and > > then wait for migration. After the source device is received, the compare fails > > due to those bits being different. > > > > But anyway, there is some chance the device will be hot-unplugged by the guest > OS for any reason, so we need to cover this scenario so it does not break > migration. > > > > > > > > > > > > > > > My understanding is that when ACPI_PM_PROP_ACPI_PCIHP_BRIDGE is off for the > > > > > device, we just won't ever PCI_EXP_SLTSTA_PDS bit? > > > > > > > > Why? > > > > > > Never mind, spoke too soon, sorry. :( > > > > > > I thought pcie_cap_slot_plug_cb() can skip the set, but then I just found > > > that dev->hotplugged is not what I imagined there. > > > > > > Leo should know better. > > > > There is a difference of which hotplug function is called based on the > > ACPI_PM_PROP_ACPI_PCIHP_BRIDGE option: > > > > When ACPI_PM_PROP_ACPI_PCIHP_BRIDGE=="off", hotplug_handler_plug() calls > > pcie_cap_slot_plug_cb() which sets the bus dev->config byte 0x6e with bit > > PCI_EXP_SLTSTA_PDS. > > > > When ACPI_PM_PROP_ACPI_PCIHP_BRIDGE=="on", hotplug_handler_plug() calls > > ich9_pm_device_plug_cb(), which does not set this bit. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > To avoid this fake incompatibility, there are two fields in PCIDevice that > > > > > > > > can help: > > > > > > > > > > > > > > > > .wmask: Used to implement R/W bytes, and > > > > > > > > .w1cmask: Used to implement RW1C(Write 1 to Clear) bytes > > > > > > > > > > > > > > Is there one more option to clear the bit in cmask? > > > > We could clear the bit for .cmask . I suggested w1cmask because I previously > > understood that bit was guest-writeable. > > IIUC, the bit is guest-writeable, so we should use .wmask instead of .cmask . > Is this correct? > > > > > > > > > > > > > > > > > IIUC w1cmask means the guest can now write to this bit, but afaiu from the > > > > > > > pcie spec it's RO. > > > > > > > > > > > > Yes this bit must be RO. > > > > My bad, I assumed behavior based on how the guest was working, and this gone > > wrong. With above documentation provided, I would suggest clearing the .config > > mask related bit so qemu skips checking this one. > > > > What is your opinion on that? > > > > > > > > > > > > > > > > > > > > > > > > According to pcie_cap_slot_init() the slot status register > > > > > > > > (PCI_EXP_SLTSTA), in which PCI_EXP_SLTSTA_PDS is a flag, seems to fall > > > > > > > > under w1cmask field, with makes sense due to the way signaling the hotplug > > > > > > > > works. > > > > > > > > > > > > > > > > So, add PCI_EXP_SLTSTA_PDS bit to w1cmask, so the fake incompatibility on > > > > > > > > get_pci_config_device() does not abort the migration. > > > > > > > > > > > > > > > > Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2215819 > > > > > > > > Signed-off-by: Leonardo Bras > > > > > > > > > > > > > > Do we need a Fixes: and also the need to copy stable? > > > > > > > > > > > > > > > --- > > > > > > > > hw/pci/pcie.c | 2 +- > > > > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > > > > > > > diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c > > > > > > > > index b8c24cf45f..2def1765a5 100644 > > > > > > > > --- a/hw/pci/pcie.c > > > > > > > > +++ b/hw/pci/pcie.c > > > > > > > > @@ -657,7 +657,7 @@ void pcie_cap_slot_init(PCIDevice *dev, PCIESlot *s) > > > > > > > > PCI_EXP_SLTCTL_EIC); > > > > > > > > > > > > > > > > pci_word_test_and_set_mask(dev->w1cmask + pos + PCI_EXP_SLTSTA, > > > > > > > > - PCI_EXP_HP_EV_SUPPORTED); > > > > > > > > + PCI_EXP_HP_EV_SUPPORTED | PCI_EXP_SLTSTA_PDS); > > > > > > > > > > > > > > > > dev->exp.hpev_notified = false; > > > > > > > > > > > > > > > > -- > > > > > > > > 2.41.0 > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > Peter Xu > > > > > > > > > > > > > > > > -- > > > > > Peter Xu > > > > > > > > >