Re: [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable

[Thomas Gleixner]

On Sat, Aug 28 2021 at 22:04, Al Viro wrote:

> On Sat, Aug 28, 2021 at 11:47:03PM +0200, Thomas Gleixner wrote:
>
>>   /* Try to handle #PF, but anything else is fatal. */
>>   if (ret != -EFAULT)
>>      return -EINVAL;
>
>> which all end up in user_insn(). user_insn() returns 0 or the negated
>> trap number, which results in -EFAULT for #PF, but for #MC the negated
>> trap number is -18 i.e. != -EFAULT. IOW, there is no endless loop.
>> 
>> This used to be a problem before commit:
>> 
>>   aee8c67a4faa ("x86/fpu: Return proper error codes from user access functions")
>> 
>> and as the changelog says the initial reason for this was #GP going into
>> the fault path, but I'm pretty sure that I also discussed the #MC angle with
>> Borislav back then. Should have added some more comments there
>> obviously.
>
> ... or at least have that check spelled
>
> 	if (ret != -X86_TRAP_PF)
> 		return -EINVAL;
>
> Unless I'm misreading your explanation, that is...

Yes, that makes a lot of sense.