Re: [PATCH v3 2/7] uaccess: Tell user_access_begin() if it's for a write or not

On Thu, Jan 23, 2020 at 4:59 AM Christophe Leroy
[off-list ref] wrote:

On 32 bits powerPC (book3s/32), only write accesses to user are
protected and there is no point spending time on unlocking for reads.

Honestly, I'm starting to think that 32-bit ppc just needs to look
more like everybody else, than make these changes.

We used to have a read/write argument to the old "verify_area()" and
"access_ok()" model, and it was a mistake. It was due to odd i386 user
access issues. We got rid of it. I'm not convinced this is any better
- it looks very similar and for odd ppc access issues.

But if we really do want to do this, then:

Add an argument to user_access_begin() to tell when it's for write and
return an opaque key that will be used by user_access_end() to know
what was done by user_access_begin().

You should make it more opaque than "unsigned long".

Also, it shouldn't be a "is this a write". What if it's a read _and_ a
write? Only a write? Only a read?

                    Linus