linux-kernel - Re: [PATCH v2 0/2] Replace and improve "mcsafe" with copy

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Message-Id: <1AA57F55-0361-4230-82B3-B432C40C0DBC@amacapital.net>
Date:   Thu, 30 Apr 2020 18:10:08 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        stable <stable@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paul Mackerras <paulus@...ba.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Erwin Tsaur <erwin.tsaur@...el.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/2] Replace and improve "mcsafe" with copy_safe()



> On Apr 30, 2020, at 5:40 PM, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> On Thu, Apr 30, 2020 at 5:23 PM Andy Lutomirski <luto@...capital.net> wrote:
>> 
>>> But anyway, I don't hate something like "copy_to_user_fallible()"
>>> conceptually. The naming needs to be fixed, in that "user" can always
>>> take a fault, so it's the _source_ that can fault, not the "user"
>>> part.
>> 
>> I don’t like this.  “user” already implied that basically anything can be wrong with the memory
> 
> Maybe I didn't explain.
> 
> "user" already implies faulting. We agree.
> 
> And since we by definition cannot know what the user has mapped into
> user space, *every* normal copy_to_user() has to be able to handle
> whatever faults that throws at us.
> 
> The reason I dislike "copy_to_user_fallible()" is that the user side
> already has that 'fallible".
> 
> If it's the _source_ being "fallible" (it really needs a better name -
> I will not call it just "f") then it should be "copy_f_to_user()".
> 
> That would be ok.
> 
> So "copy_f_to_user()" makes sense. But "copy_to_user_f()" does not.
> That puts the "f" on the "user", which we already know can fault.
> 
> See what I want in the name? I want the name to say which side can
> cause problems!

We are in violent agreement. I’m moderately confident that I never suggested copy_from_user_f(). We appear to agree completely.