On Wed, Nov 14, 2018 at 07:22:04PM +0000, Alex_Gagniuc@xxxxxxxxxxxx wrote: > On 11/14/2018 12:00 AM, Bjorn Helgaas wrote: > > On Tue, Nov 13, 2018 at 10:39:15PM +0000, Alex_Gagniuc@xxxxxxxxxxxx wrote: > >> On 11/12/2018 11:02 PM, Bjorn Helgaas wrote: > >> ... > >>> Do you think Linux observes the rule about not touching AER bits on > >>> FFS? I'm not sure it does. I'm not even sure what section of the > >>> spec is relevant. > >> > >> I haven't found any place where linux breaks this rule. I'm very > >> confident that, unless otherwise instructed, we follow this rule. > > > > Just to make sure we're on the same page, can you point me to this > > rule? I do see that OSPM must request control of AER using _OSC > > before it touches the AER registers. What I don't see is the > > connection between firmware-first and the AER registers. > > ACPI 6.2 - 6.2.11.3, Table 6-197: > > PCI Express Advanced Error Reporting control: > * The firmware sets this bit to 1 to grant control over PCI Express > Advanced Error Reporting. If firmware allows the OS control of this > feature, then in the context of the _OSC method it must ensure that > error messages are routed to device interrupts as described in the PCI > Express Base Specification[...] The PCIe Base Spec is pretty big, so I wish this reference were a little more explicit. I *guess* maybe it's referring to PCIe r4.0, figure 6-3 in sec 6.2.6, where PCIe ERR_* Messages can be routed to "INTx or MSI Error Interrupts" and/or "platform-specific System Error" interrupts. "Device interrupts" seems like it refers to the "INTx or MSI" interrupts, not the platform-specific System Errors, so I would read that as saying "if firmware grants OS control of AER via _OSC, firmware must set the AER Reporting Enables in the AER Root Error Command register." But that seems a little silly because the OS now *owns* the AER capability and it can set the AER Root Error Command register itself if it wants to. And I still don't see the connection here with Firmware-First. I'm pretty sure firmware could not be notified via INTx or MSI interrupts because those are totally managed by OSPM. > > The closest I can find is the "Enabled" field in the HEST PCIe > > AER structures (ACPI v6.2, sec 18.3.2.4, .5, .6), where it says: > > > > If the field value is 1, indicates this error source is > > to be enabled. > > > > If the field value is 0, indicates that the error source > > is not to be enabled. > > > > If FIRMWARE_FIRST is set in the flags field, the Enabled > > field is ignored by the OSPM. > > > > AFAICT, Linux completely ignores the Enabled field in these > > structures. > > I don't think ignoring the field is a problem: > * With FFS, OS should ignore it. > * Without FFS, we have control, and we get to make the decisions anyway. > In the latter case we decide whether to use AER, independent of the crap > in ACPI. I'm not even sure why "Enabled" matters in native AER handling. It seems like these HEST structures are "here's how firmware thinks you should set up AER on this device". But I agree, I have no idea how to interpret "Enabled". The rest of the HEST fields cover all the useful AER registers, including the Reporting Enables in the AER Root Error Command register *and* the Error Reporting Enables in the Device Control register. So I don't know what the "Enabled" field adds to all that. What a mess. > > For firmware-first to work, firmware has to get control. How does > > it get control? How does OSPM know to either set up that > > mechanism or keep its mitts off something firmware set up before > > handoff? > > My understanding is that, if FW keeps control of AER in _OSC, then > it will have set things up to get notified instead of the OS. OSPM > not touching AER bits is to make sure it doesn't mess up FW's setup. > I think there are some proprietary bits in the root port to route > interrupts to SMIs instead of the AER vectors. It makes good sense that if OSPM doesn't have AER control, firmware does all AER handling, including any setup for firmware-first notification. If we can assume that firmware-first notification is done in some way the OS doesn't know about and can't mess up, that would be awesome. But I think the VMD model really has nothing to do with the APEI firmware-first model. With VMD, it sounds like OSPM owns the AER capability and doesn't know firmware exists *except* that it has to be careful not to step on firmware's interrupt. So maybe we can handle it separately. Bjorn