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Message-ID: <13319e46cf2a8caa0b397ef67db7d406261a64b0.camel@redhat.com>
Subject: Re: [PATCH v5 RESEND 1/5] lib/pci_iomap.c: fix cleanup bugs in
 pci_iounmap()
From: Philipp Stanner <pstanner@redhat.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>, Arnd Bergmann <arnd@arndb.de>, 
 Johannes Berg <johannes@sipsolutions.net>, Randy Dunlap
 <rdunlap@infradead.org>, NeilBrown <neilb@suse.de>,  John Sanpe
 <sanpeqf@gmail.com>, Kent Overstreet <kent.overstreet@gmail.com>, Niklas
 Schnelle <schnelle@linux.ibm.com>, Dave Jiang <dave.jiang@intel.com>,
 Uladzislau Koshchanka <koshchanka@gmail.com>, "Masami Hiramatsu (Google)"
 <mhiramat@kernel.org>, David Gow <davidgow@google.com>, Kees Cook
 <keescook@chromium.org>, Rae Moar <rmoar@google.com>, Geert Uytterhoeven
 <geert@linux-m68k.org>, "wuqiang.matt" <wuqiang.matt@bytedance.com>, Yury
 Norov <yury.norov@gmail.com>, Jason Baron <jbaron@akamai.com>, Thomas
 Gleixner <tglx@linutronix.de>, Marco Elver <elver@google.com>, Andrew
 Morton <akpm@linux-foundation.org>, Ben Dooks <ben.dooks@codethink.co.uk>,
 dakr@redhat.com, linux-kernel@vger.kernel.org,  linux-pci@vger.kernel.org,
 linux-arch@vger.kernel.org, stable@vger.kernel.org,  Arnd Bergmann
 <arnd@kernel.org>
Date: Thu, 25 Jan 2024 17:06:38 +0100
In-Reply-To: <20240123184622.GA322265@bhelgaas>
References: <20240123184622.GA322265@bhelgaas>
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On Tue, 2024-01-23 at 12:46 -0600, Bjorn Helgaas wrote:
> On Thu, Jan 11, 2024 at 09:55:36AM +0100, Philipp Stanner wrote:
> > pci_iounmap() in lib/pci_iomap.c is supposed to check whether an
> > address
> > is within ioport-range IF the config specifies that ioports exist.
> > If
> > so, the port should be unmapped with ioport_unmap(). If not, it's a
> > generic MMIO address that has to be passed to iounmap().
> >=20
> > The bugs are:
> > =C2=A0 1. ioport_unmap() is missing entirely, so this function will
> > never
> > =C2=A0=C2=A0=C2=A0=C2=A0 actually unmap a port.
>=20
> The preceding comment suggests that in this default implementation,
> the ioport does not need unmapping, and it wasn't something it was
> supposed to do but just failed to do:
>=20
> =C2=A0* NOTE! This default implementation assumes that if the architectur=
e
> =C2=A0* support ioport mapping (HAS_IOPORT_MAP), the ioport mapping will
> =C2=A0* be fixed to the range [ PCI_IOBASE, PCI_IOBASE+IO_SPACE_LIMIT [,
> =C2=A0* and does not need unmapping with 'ioport_unmap()'.
> =C2=A0*
> =C2=A0* If you have different rules for your architecture, you need to
> =C2=A0* implement your own pci_iounmap() that knows the rules for where
> =C2=A0* and how IO vs MEM get mapped.
>=20
> Almost all ioport_unmap() implementations are empty, so in most cases
> it's a no-op (parisc is an exception).

That sounds correct.

>=20
> I'm happy to add the ioport_unmap() even just for symmetry, but if we
> do, I think we should update or remove that comment.

Yes, I think it's the right way: either all architectures should
provide ioport_unmap(), empty or not, or all should use a centralized
PCI function

I can remove the wrong statement.

>=20
> > =C2=A0 2. the #ifdef for the ioport-ranges accidentally also guards
> > =C2=A0=C2=A0=C2=A0=C2=A0 iounmap(), potentially compiling an empty func=
tion. This would
> > =C2=A0=C2=A0=C2=A0=C2=A0 cause the mapping to be leaked.
> >=20
> > Implement the missing call to ioport_unmap().
> >=20
> > Move the guard so that iounmap() will always be part of the
> > function.
>=20
> I think we should fix this bug in a separate patch because the
> ioport_unmap() is much more subtle and doesn't need to be complicated
> with this fix.

If we agree that one is a bug and the other isn't, then ACK, we should
probably split it.

>=20
> > CC: <stable@vger.kernel.org> # v5.15+
> > Fixes: 316e8d79a095 ("pci_iounmap'2: Electric Boogaloo: try to make
> > sense of it all")
> > Reported-by: Danilo Krummrich <dakr@redhat.com>
>=20
> Is there a URL we can include for Danilo's report?=C2=A0 I found
> https://lore.kernel.org/all/a6ef92ae-0747-435b-822d-d0229da4683c@redhat.c=
om/
> ,
> but I'm not sure that's the right part of the conversation.

He pointed out it's a bug in an offlist conversation with me. The link
you provided is his only public statement about the topic.
The Reported-by served more acknowledging the contribution than issue-
tracking


P.

>=20
> > Suggested-by: Arnd Bergmann <arnd@kernel.org>
> > Signed-off-by: Philipp Stanner <pstanner@redhat.com>
> > Reviewed-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> > =C2=A0lib/pci_iomap.c | 6 ++++--
> > =C2=A01 file changed, 4 insertions(+), 2 deletions(-)
> >=20
> > diff --git a/lib/pci_iomap.c b/lib/pci_iomap.c
> > index ce39ce9f3526..6e144b017c48 100644
> > --- a/lib/pci_iomap.c
> > +++ b/lib/pci_iomap.c
> > @@ -168,10 +168,12 @@ void pci_iounmap(struct pci_dev *dev, void
> > __iomem *p)
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0uintptr_t start =3D (ui=
ntptr_t) PCI_IOBASE;
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0uintptr_t addr =3D (uin=
tptr_t) p;
> > =C2=A0
> > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (addr >=3D start && addr =
< start + IO_SPACE_LIMIT)
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (addr >=3D start && addr =
< start + IO_SPACE_LIMIT) {
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0ioport_unmap(p);
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0return;
> > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0iounmap(p);
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0}
> > =C2=A0#endif
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0iounmap(p);
> > =C2=A0}
> > =C2=A0EXPORT_SYMBOL(pci_iounmap);
> > =C2=A0
> > --=20
> > 2.43.0
> >=20
>=20