linux-kernel - Re: [PATCH v2 2/2] serial: 8250_lpss: Switch to pcim_iomap() instead of pci_ioremap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YhUJAl5JpCoXik7X@infradead.org>
Date:   Tue, 22 Feb 2022 08:02:10 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Jiri Slaby <jirislaby@...nel.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2 2/2] serial: 8250_lpss: Switch to pcim_iomap() instead
 of pci_ioremap_bar()

On Tue, Feb 22, 2022 at 10:14:16AM +0100, Jiri Slaby wrote:
> On 16. 02. 22, 9:53, Christoph Hellwig wrote:
> > On Tue, Feb 15, 2022 at 03:43:59PM +0200, Andy Shevchenko wrote:
> > > The pci_iounmap() doesn't cover all the cases where resource should
> > > be unmapped. Instead of spreading it more, replace the pci_ioremap_bar()
> > > with pcim_iomap() which uses managed resource approach.
> > 
> > pcim_iomap requires the use of ioreadX/iowriteX and thus runtime
> > overhead.  So in doubt please add a pcim_ioremap_bar instead of forcing
> > the legacy iomap/ioread/iowrite API onto modern drivers tht can't
> > support legacy port I/O.
> 
> Hmm, the driver combines pci_ioremap_bar with pci_iounmap. pci_iounmap does
> the right thing after all, but is that correct? And this driver is not
> alone, this shows more:
> git grep -E 'pci_iounmap|pci_ioremap_bar' `git grep -l pci_iounmap \`git
> grep -l pci_ioremap_bar\``

I think it is wrong.  It is not actively harmful unlike the the
combination of pci_iomap and then later use of accessors from the
ioremap family, but still not exactly a good idea.

In a perfect world we'd have some different annotation from __iomem
for the whole iomap family of functions.