On 11/9/2021 1:02 PM, Dan Williams wrote:
> On Tue, Nov 9, 2021 at 11:59 AM Jane Chu <jane.chu@xxxxxxxxxx> wrote:
>>
>> On 11/9/2021 10:48 AM, Dan Williams wrote:
>>> On Mon, Nov 8, 2021 at 11:27 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>>>>
>>>> On Fri, Nov 05, 2021 at 07:16:38PM -0600, Jane Chu wrote:
>>>>> static size_t pmem_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff,
>>>>> void *addr, size_t bytes, struct iov_iter *i, int mode)
>>>>> {
>>>>> + phys_addr_t pmem_off;
>>>>> + size_t len, lead_off;
>>>>> + struct pmem_device *pmem = dax_get_private(dax_dev);
>>>>> + struct device *dev = pmem->bb.dev;
>>>>> +
>>>>> + if (unlikely(mode == DAX_OP_RECOVERY)) {
>>>>> + lead_off = (unsigned long)addr & ~PAGE_MASK;
>>>>> + len = PFN_PHYS(PFN_UP(lead_off + bytes));
>>>>> + if (is_bad_pmem(&pmem->bb, PFN_PHYS(pgoff) / 512, len)) {
>>>>> + if (lead_off || !(PAGE_ALIGNED(bytes))) {
>>>>> + dev_warn(dev, "Found poison, but addr(%p) and/or bytes(%#lx) not page aligned\n",
>>>>> + addr, bytes);
>>>>> + return (size_t) -EIO;
>>>>> + }
>>>>> + pmem_off = PFN_PHYS(pgoff) + pmem->data_offset;
>>>>> + if (pmem_clear_poison(pmem, pmem_off, bytes) !=
>>>>> + BLK_STS_OK)
>>>>> + return (size_t) -EIO;
>>>>> + }
>>>>> + }
>>>>
>>>> This is in the wrong spot. As seen in my WIP series individual drivers
>>>> really should not hook into copying to and from the iter, because it
>>>> really is just one way to write to a nvdimm. How would dm-writecache
>>>> clear the errors with this scheme?
>>>>
>>>> So IMHO going back to the separate recovery method as in your previous
>>>> patch really is the way to go. If/when the 64-bit store happens we
>>>> need to figure out a good way to clear the bad block list for that.
>>>
>>> I think we just make error management a first class citizen of a
>>> dax-device and stop abstracting it behind a driver callback. That way
>>> the driver that registers the dax-device can optionally register error
>>> management as well. Then fsdax path can do:
>>>
>>> rc = dax_direct_access(..., &kaddr, ...);
>>> if (unlikely(rc)) {
>>> kaddr = dax_mk_recovery(kaddr);
>>
>> Sorry, what does dax_mk_recovery(kaddr) do?
>
> I was thinking this just does the hackery to set a flag bit in the
> pointer, something like:
>
> return (void *) ((unsigned long) kaddr | DAX_RECOVERY)
Okay, how about call it dax_prep_recovery()?
>
>>
>>> dax_direct_access(..., &kaddr, ...);
>>> return dax_recovery_{read,write}(..., kaddr, ...);
>>> }
>>> return copy_{mc_to_iter,from_iter_flushcache}(...);
>>>
>>> Where, the recovery version of dax_direct_access() has the opportunity
>>> to change the page permissions / use an alias mapping for the access,
>>
>> again, sorry, what 'page permissions'? memory_failure_dev_pagemap()
>> changes the poisoned page mem_type from 'rw' to 'uc-' (should be NP?),
>> do you mean to reverse the change?
>
> Right, the result of the conversation with Boris is that
> memory_failure() should mark the page as NP in call cases, so
> dax_direct_access() needs to create a UC mapping and
> dax_recover_{read,write}() would sink that operation and either return
> the page to NP after the access completes, or convert it to WB if the
> operation cleared the error.
Okay, will add a patch to fix set_mce_nospec().
How about moving set_memory_uc() and set_memory_np() down to
dax_recovery_read(), so that we don't split the set_memory_X calls
over different APIs, because we can't enforce what follows
dax_direct_access()?
>
>>> dax_recovery_read() allows reading the good cachelines out of a
>>> poisoned page, and dax_recovery_write() coordinates error list
>>> management and returning a poison page to full write-back caching
>>> operation when no more poisoned cacheline are detected in the page.
>>>
>>
>> How about to introduce 3 dax_recover_ APIs:
>> dax_recover_direct_access(): similar to dax_direct_access except
>> it ignores error list and return the kaddr, and hence is also
>> optional, exported by device driver that has the ability to
>> detect error;
>> dax_recovery_read(): optional, supported by pmem driver only,
>> reads as much data as possible up to the poisoned page;
>
> It wouldn't be a property of the pmem driver, I expect it would be a
> flag on the dax device whether to attempt recovery or not. I.e. get
> away from this being a pmem callback and make this a native capability
> of a dax device.
>
>> dax_recovery_write(): optional, supported by pmem driver only,
>> first clear-poison, then write.
>>
>> Should we worry about the dm targets?
>
> The dm targets after Christoph's conversion should be able to do all
> the translation at direct access time and then dax_recovery_X can be
> done on the resulting already translated kaddr.
I'm thinking about the mixed device dm where some provides
dax_recovery_X, others don't, in which case we don't allow
dax recovery because that causes confusion? or should we still
allow recovery for part of the mixed devices?
>
>> Both dax_recovery_read/write() are hooked up to dax_iomap_iter().
>
> Yes.
>
thanks!
-jane
