On Wed, Feb 27, 2019 at 04:42:05PM +0000, alex_gagn...@dellteam.com wrote: > On 2/26/19 7:02 PM, Linus Torvalds wrote: > > On Tue, Feb 26, 2019 at 2:37 PM <alex_gagn...@dellteam.com> wrote: > >> > >> Then nobody gets the (error) message. You can go a bit further and try > >> 'pcie_ports=native". Again, nobody gets the memo. ): > > > > So? The error was bogus to begin with. Why would we care? > > Of course nobody cares about that. We care about actual errors that we > now know we won't be notified of. Imagine if we didn't get the memo that > a piece of data is corrupt, and imagine the reaction of RAS folk. > > And I know the counter to that is a panic() is much more likely to cause > data corruption, and we're trading one piece of crap for an even > stinkier one. Whatever we end up doing, we have to do better than > silence errors and pretend nothing happened. > > > > Yes, yes, PCI bridges have the ability to return errors in accesses to > > non-existent devices. But that was always bogus, and is never useful. > > The whole "you get an interrupt or NMI on a bad access" is simply a > > horribly broken model. It's not useful. > > > > We already have long depended on hotplug drivers noticing the "oh, I'm > > getting all-ff returns, the device may be gone". It's usually trivial, > > and works a whole lot better. > > And that's been working great, hasn't it? I think you're thinking > strictly about hotplug. There are other situations where things are all > F'd, but the hardware isn't sending all F's. (example: ECRC errors) > > > > It's not an error. Trying to force it to be an NMI or SCI or machine > > check is bogus. It causes horrendous pain, because asynchronous > > reporting doesn't work reliably anyway, and *synchronous* reporting is > > impossible to sanely handle without crazy problems. > > > > So the only sane model for hotplug devices is "IO still works, and > > returns all ones". Maybe with an async one-time and *recoverable* > > machine check or other reporting the access after the fact. > > Exactly!!! A notification (not calling it an 'error') that something > unusual has happened is good. Treating these things like errors is so > obvious, even a caveman wouldn't do it. > In a world with FFS, we don't always get to have that model. Oh, FFS! > > > > Anything else is simply broken. It would be broken even if firmware > > wasn't involved, but obviously firmware people tend to often make a > > bad situation even worse. > > Linus, be nice to firmware people. I've met a few, and I can vouch that > they're very kind and nice. They're also very scared, especially when OS > people want to ask them a few questions. > > I think FFS should get out of the way when OS advertises it's capable of > handling XYZ. There are some good arguments why this hasn't happened, > but I won't get into details. I do think it's unlikely that machines > will be moving back to an OS-controlled model. > > And Linus, keep in mind, when these machines were developed, OSes > couldn't handle recovery properly. None of this was ever an issue. It's > our fault that we've changed the OS after the machines are on the market. > > Alex
I can't tell where you're going with this. It doesn't sound like you're talking about hotplug anymore, at least.
