Messages in this thread | | | Date | Fri, 17 Jun 2022 09:29:35 -0700 | From | Alison Schofield <> | Subject | Re: [PATCH 2/3] cxl/mbox: Add GET_POISON_LIST mailbox command support |
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On Fri, Jun 17, 2022 at 07:05:08AM -0700, Jonathan Cameron wrote: > On Tue, 14 Jun 2022 17:10:27 -0700 > alison.schofield@intel.com wrote: > > > From: Alison Schofield <alison.schofield@intel.com> > > > > CXL devices that support persistent memory maintain a list of locations > > that are poisoned or result in poison if the addresses are accessed by > > the host. > > > > Per the spec (CXL 2.0 8.2.8.5.4.1), the device returns this Poison > > list as a set of Media Error Records that include the source of the > > error, the starting device physical address and length. The length is > > the number of adjacent DPAs in the record and is in units of 64 bytes. > > > > Retrieve the list and log each Media Error Record as a trace event of > > type cxl_poison_list. > > > > Signed-off-by: Alison Schofield <alison.schofield@intel.com> > > A few more things inline. > > Otherwise, can confirm it works with some hack QEMU code. > I'll tidy that up and post soon. > > > +int cxl_mem_get_poison_list(struct device *dev) > > +{ snip > > + > > + trace_cxl_poison_list(dev, source, addr, len); > > Need to mask off the lower 6 bits of addr as they contain the source > + a few reserved bits. > > I was confused how you were geting better than 64 byte precision in your > example. > Ah...got it. Thanks!
> > + } > > + > > + /* Protect against an uncleared _FLAG_MORE */ > > + nr_records = nr_records + le16_to_cpu(po->count); > > + if (nr_records >= cxlds->poison_max) > > + goto out; > > + > > + } while (po->flags & CXL_POISON_FLAG_MORE); > So.. A conundrum here. What happens if: > > 1. We get an error mid way through a set of multiple reads > (something intermittent - maybe a software issue) > 2. We will drop out of here fine and report the error. > 3. We run this function again. > > It will (I think) currently pick up where we left off, but we have > no way of knowing that as there isn't a 'total records' count or > any other form of index in the output payload.
Yes. That is sad. I'm assume it's by design and CXL devices never intended to keep any totals.
> > So, software solutions I think should work (though may warrant a note > to be added to the spec). > > 1. Read whole thing twice. First time is just to ensure we get > to the end and flush out any prior half done reads. > 2. Issue a read for a different region (perhaps length 0) first > and assume everything starts from scratch when we go back to > this region.
Can you tell me more about 2 ?
Also, Since posting this I have added protection to this path to ensure only one reader of the poison list for this device. Like this:
if (!completion_done(&cxlds->read_poison_complete); return -EBUSY; wait_for_completion_interruptible(&cxlds->read_poison_complete); ...GET ALL THE POISON... complete(&cxlds->read_poison_complete);
And will add the error message on that unexpected _FLAG_MORE too.
Alison > > Jonathan >
> > + > > +out: > > + kvfree(po); > > + return rc; > > +} > > +EXPORT_SYMBOL_NS_GPL(cxl_mem_get_poison_list, CXL); > > + > > struct cxl_dev_state *cxl_dev_state_create(struct device *dev) > > { > > struct cxl_dev_state *cxlds; >
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