Re: [PATCH] arm: Extend the check for RAM in /dev/mem
From: Russell King - ARM Linux admin
Date: Fri Jul 12 2019 - 04:56:17 EST
On Fri, Jul 12, 2019 at 02:58:18AM +0000, Raslan, KarimAllah wrote:
> On Fri, 2019-07-12 at 08:06 +0530, Anshuman Khandual wrote:
> > On 07/12/2019 03:51 AM, KarimAllah Ahmed wrote:
> > >
> > > Some valid RAM can live outside kernel control (e.g. using mem= kernel
> > > command-line). For these regions, pfn_valid would return "false" causing
> > > system RAM to be mapped as uncached. Use memblock instead to identify RAM.
> > Once the remaining memory is outside of the kernel (as the admin would have
> > intended with mem= command line) what is the particular concern regarding
> > the way those get mapped (cached or not) ? It is not to be used any way.
> They can be used by user-space which might lead to them being used by the
> kernel. One use-case would be using them as guest memory for KVM as I detailed
>From the 32-bit ARM point of view...
What if someone's already doing something similar with a non-coherent
DSP and is relying on the current behaviour? This change is a user
visible behavioural change that could end up breaking userspace.
In other words, it isn't something we should rush into.
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up