Re: [PATCH] io_uring: don't allow IORING_SETUP_NO_MMAP rings on highmem pages

[Jens Axboe <axboe@kernel.dk>]

On 10/3/23 12:24 PM, Jeff Moyer wrote:
> Jens Axboe <axboe@kernel.dk> writes:
> 
>> On 10/3/23 10:30 AM, Jeff Moyer wrote:
>>> Hi, Jens,
>>>
> [snip]
>>> What do you think about throwing a printk_once in there that explains
>>> the problem?  I'm worried that this will fail somewhat randomly, and it
>>> may not be apparent to the user why.  We should also add documentation,
>>> of course, and encourage developers to add fallbacks for this case.
>>
>> For both cases posted, it's rather more advanced use cases. And 32-bit
>> isn't so prevalent anymore, thankfully. I was going to add to the man
>> pages explaining this failure case. Not sure it's worth adding a printk
>> for though.
> 
> I try not to make decisions based on how prevalent I think a particular
> configuration is (mainly because I'm usually wrong).  Anyway, it's not a
> big deal, I'm glad you gave it some thought.

Me neither, but I think we can all safely agree that 32-bit highmem is
thankfully not on the uptick :-)

>> FWIW, once I got an arm32 vm setup, it fails everytime for me. Not sure
>> how it'd do on 32-bit x86, similarly or more randomly. But yeah it's
>> definitely at the mercy of how things are mapped.
> 
> ...and potentially the load on the system.  Anyway, it's fine with me to
> keep it as is.  We can always add a warning later if it ends up being a
> problem.

Certainly!

-- 
Jens Axboe