Messages in this thread | | | Date | Fri, 12 Jul 2019 09:56:02 +0100 | From | Russell King - ARM Linux admin <> | Subject | Re: [PATCH] arm: Extend the check for RAM in /dev/mem |
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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 > here: > > https://lwn.net/Articles/778240/
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
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