From: Michael Schmitz <schmitzmic@gmail.com>
To: Finn Thain <fthain@linux-m68k.org>
Cc: geert@linux-m68k.org, linux-m68k@lists.linux-m68k.org
Subject: Re: [PATCH RFC v2 1/2] m68k: Handle __generic_copy_to_user faults more carefully
Date: Thu, 25 Apr 2024 19:52:35 +1200 [thread overview]
Message-ID: <eda396cb-9c7a-f312-0159-2d4c411798bb@gmail.com> (raw)
In-Reply-To: <36a70661-3bfc-46f1-f211-fa87f883371a@linux-m68k.org>
Hi Finn,
Am 25.04.2024 um 18:32 schrieb Finn Thain:
>>> This oops indicates that we are going to need the final NOP that was
>>> in the first version of your patch. My test program seems inadequate
>>> to show that it is safe to omit that NOP -- we would need a test which
>>> doesn't jump over the MOVES.B.
>>
>> We'd need a test using any number of longword moves expected to succeed,
>> followed by a byte move which is expected to fault. The current test
>> would attempt to do a byte move, but faults during the longword moves.
>>
>> This requires running the test program in a directory whose absolute
>> path is a multiple of four characters long, and setting the start
>> address for the getcwd test accordingly, so the newline at the end of
>> the string is the single byte left to copy. Does that make sense?
>>
>
> Yes (I take it you meant NUL instead of LF). But my concern was that the
Yes, my bad ...
> test program passes a pointer like 0xc0029000 - 1. That means the final
> byte will land on a word that already faulted. I'll need to add a new test
> that passes a pointer like 0xc0029000 - 5.
That's what I meant to say, yes.
>> Incidentally - what is the path this tests is run in? Any path longer
>> than five characters (including the newline) would have to had looped
>> back to the first movel, and faulted there?
>>
>
> It was /tmp.
Right - so if I'm right, running the test in /root would exercise the
movesw path, and fault on the movew. Using /var/tmp would loop back once
to repeat the movesl, and likely fault on the movel there.
>> As you said before - we'd need to know a lot more about
>> microarchitectural details here.
>>
>
> It's hard to be certain. We just have to experiment until we find
> something that works on the CPUs we can test.
Right - I'll try a few of these ideas on my 030.
Cheers,
Michael
next prev parent reply other threads:[~2024-04-25 7:52 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-22 2:29 [PATCH RFC v2 0/2] m68k uaccess fault handling fixes Michael Schmitz
2024-04-22 2:29 ` [PATCH RFC v2 1/2] m68k: Handle __generic_copy_to_user faults more carefully Michael Schmitz
2024-04-25 4:16 ` Finn Thain
2024-04-25 5:32 ` Michael Schmitz
2024-04-25 6:32 ` Finn Thain
2024-04-25 7:52 ` Michael Schmitz [this message]
2024-04-25 5:45 ` Michael Schmitz
2024-04-25 6:47 ` Finn Thain
2024-04-25 7:43 ` Michael Schmitz
2024-04-25 8:20 ` Michael Schmitz
2024-04-25 19:15 ` Michael Schmitz
2024-04-26 1:00 ` Finn Thain
2024-04-26 1:22 ` Michael Schmitz
2024-04-26 7:10 ` Michael Schmitz
2024-04-26 7:57 ` Finn Thain
2024-04-26 8:31 ` Michael Schmitz
2024-04-26 7:58 ` Finn Thain
2024-04-27 1:44 ` Finn Thain
2024-04-27 4:41 ` Michael Schmitz
2024-04-22 2:29 ` [PATCH RFC v2 2/2] m68k: improve __constant_copy_to_user_asm() fault handling Michael Schmitz
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