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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [PATCH v2 0/2] Replace and improve "mcsafe" with copy_safe()
Date:   Thu, 30 Apr 2020 18:10:08 -0700
Message-Id: <1AA57F55-0361-4230-82B3-B432C40C0DBC@amacapital.net>
References: <CAHk-=wgeMRm_yhb_fwvmgdaPMYzgXY01cYvw5htHUCTwSzswqg@mail.gmail.com>
Cc:     Dan Williams <dan.j.williams@intel.com>,
        "Luck, Tony" <tony.luck@intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>,
        stable <stable@vger.kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Paul Mackerras <paulus@samba.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Erwin Tsaur <erwin.tsaur@intel.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        linux-nvdimm <linux-nvdimm@lists.01.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
In-Reply-To: <CAHk-=wgeMRm_yhb_fwvmgdaPMYzgXY01cYvw5htHUCTwSzswqg@mail.gmail.com>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Sender: linux-kernel-owner@vger.kernel.org
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> On Apr 30, 2020, at 5:40 PM, Linus Torvalds <torvalds@linux-foundation.org=
> wrote:
>=20
> =EF=BB=BFOn Thu, Apr 30, 2020 at 5:23 PM Andy Lutomirski <luto@amacapital.=
net> wrote:
>>=20
>>> 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.
>>=20
>> I don=E2=80=99t like this.  =E2=80=9Cuser=E2=80=9D already implied that b=
asically anything can be wrong with the memory
>=20
> Maybe I didn't explain.
>=20
> "user" already implies faulting. We agree.
>=20
> 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.
>=20
> The reason I dislike "copy_to_user_fallible()" is that the user side
> already has that 'fallible".
>=20
> 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()".
>=20
> That would be ok.
>=20
> 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.
>=20
> See what I want in the name? I want the name to say which side can
> cause problems!

We are in violent agreement. I=E2=80=99m moderately confident that I never s=
uggested copy_from_user_f(). We appear to agree completely.