From mboxrd@z Thu Jan 1 00:00:00 1970 From: nico@fluxnic.net (Nicolas Pitre) Date: Fri, 08 Oct 2010 22:41:42 -0400 (EDT) Subject: [PATCH] ARM: allow, but warn, when issuing ioremap() on RAM In-Reply-To: <20101009002546.GB14675@n2100.arm.linux.org.uk> References: <1286444662-16843-1-git-send-email-felipe.contreras@gmail.com> <20101007192245.GC26435@n2100.arm.linux.org.uk> <20101008175308.GA10975@n2100.arm.linux.org.uk> <20101008230451.GB10975@n2100.arm.linux.org.uk> <20101008232539.GA28697@kroah.com> <20101008234448.GD10975@n2100.arm.linux.org.uk> <20101009000046.GA30616@kroah.com> <20101009002546.GB14675@n2100.arm.linux.org.uk> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Sat, 9 Oct 2010, Russell King - ARM Linux wrote: > On Fri, Oct 08, 2010 at 05:00:46PM -0700, Greg KH wrote: > > But you can't expect that you make this change, and not fix up the > > drivers, and people would be happy, right? The rule for API changes > > like this, or anything, is that the person making the change fixes the > > other drivers, and that seems to be the issue here. > > Let's entirely revert the change and wait for people's data to be > corrupted then. I don't have the time nor the motivation to work > through crap driver code to fix up these unreliable games which are > already illegal on platforms such as x86. > > If people want their system to be unpredictable, then let's carry on > giving them the rope to hang themselves in that manner. > > > Any pointers to patches where people have fixed up the drivers? > > Despite the discussion, I'm unaware of anyone really taking the issue > seriously and producing any patches during the last six months. > > So, I say sod it, let's revert the change. I think that the real issue here is to avoid breaking those drivers which were using this legitimately. So what about this compromize instead: diff --git a/arch/arm/mm/ioremap.c b/arch/arm/mm/ioremap.c index 99627d3..4f071e4 100644 --- a/arch/arm/mm/ioremap.c +++ b/arch/arm/mm/ioremap.c @@ -201,6 +201,15 @@ void __iomem * __arm_ioremap_pfn_caller(unsigned long pfn, if (pfn >= 0x100000 && (__pfn_to_phys(pfn) & ~SUPERSECTION_MASK)) return NULL; + /* + * Warn if RAM is mapped to discourage this usage. Let's forbid it + * outright on ARMv6+ where this became architecturally undefined + * in theory and causes memory corruption in practice. + */ + if (WARN_ON(pfn_valid(pfn))) + if (__LINUX_ARM_ARCH__ >= 6) + return NULL; + type = get_mem_type(mtype); if (!type) return NULL; Nicolas