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Message-ID: <20170216143509.GA22820@bhelgaas-glaptop.roam.corp.google.com>
Date: Thu, 16 Feb 2017 08:35:10 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Jess Frazelle <me@...sfraz.com>, "K. Y. Srinivasan" <kys@...rosoft.com>,
Haiyang Zhang <haiyangz@...rosoft.com>,
Stephen Hemminger <sthemmin@...rosoft.com>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Keith Busch <keith.busch@...el.com>,
"open list:Hyper-V CORE AND DRIVERS" <devel@...uxdriverproject.org>,
"open list:PCI SUBSYSTEM" <linux-pci@...r.kernel.org>,
open list <linux-kernel@...r.kernel.org>,
kernel-hardening@...ts.openwall.com,
Kees Cook <keescook@...omium.org>,
Marc Zyngier <marc.zyngier@....com>
Subject: Re: [PATCH v2 3/5] pci: set msi_domain_ops as __ro_after_init
On Wed, Feb 15, 2017 at 10:16:32PM +0100, Thomas Gleixner wrote:
> I think I suggested to Jiang to do that 'update with default functions' to
>
> - avoid exporting the world and some more
>
> - have the flexibility to add new functions to the ops w/o updating a
> gazillion of existing usage sites, which has saved us lots of chaising in
> the last years
>
> - avoid the if (ops->ptr) ops->ptr(); else default_fn(); constructs all
> over the place.
>
> I admit I did not think about the fact that this makes the structs non
> const.
>
> Mopping that up by exporting the default functions and setting all the
> function pointers is tedious and requires a full tree sweep when we add new
> stuff. There's also code shared between PCI/platform/DT based stuff, so
> that becomes interesting.
It's legal to initialize a field multiple times, and the last one
takes precedence, so doing this might at least avoid the full tree
sweeps:
static struct msi_domain_ops vmd_msi_domain_ops = {
MSI_DOMAIN_DEFAULT_OPS,
.get_hwirq = vmd_get_hwirq,
};
The functions referenced by MSI_DOMAIN_DEFAULT_OPS would still have to
be exported, though.
> Doing the if (ops->ptr) ops->ptr() else default_fn(); dance should be
> simpler to pull off. There are not that many sites to look at, but then we
> have some of the GICv3 code using the domain ops out of core.
>
> For now doing the __ro_after_init is definitely the simplest and fastest
> solution to tighten these statically allocated structures.
I'm OK with __ro_after_init, at least as an interim solution.
I do think it would be good to audit all the uses of
MSI_FLAG_USE_DEF_DOM_OPS and MSI_FLAG_USE_DEF_CHIP_OPS, since they
seem to be the primary indicator of when the struct might be modified.
I suspect we could add __ro_after_init to more than just pci-hyperv.c,
vmd.c, and msi.c
Bjorn
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