On 01/04/15 16:15, Dave P Martin wrote: > Apologies for the slow reply... :/ > > Anyway, > > On Mon, Mar 23, 2015 at 06:47:53PM +0000, Daniel Thompson wrote: >> On 20/03/15 15:45, Dave Martin wrote: >>> On Wed, Mar 18, 2015 at 02:20:21PM +0000, Daniel Thompson wrote: >>>> This patchset provides a pseudo-NMI for arm64 kernels by reimplementing >>>> the irqflags macros to modify the GIC PMR (the priority mask register is >>>> accessible as a system register on GICv3 and later) rather than the >>>> PSR. The pseudo-NMI changes are support by a prototype implementation of >>>> arch_trigger_all_cpu_backtrace that allows the new code to be exercised. > > Minor nit: the "pseudo NMI" terminology could lead to confusion if > something more closely resembling a real NMI comes along. > > I'll have to have a think, but nothing comes to mind right now... > > [...] > >>>> 3. Requires GICv3+ hardware together with firmware support to enable >>>> GICv3 features at EL3. If CONFIG_USE_ICC_SYSREGS_FOR_IRQFLAGS is >>>> enabled the kernel will not boot on older hardware. It will be hard >>>> to diagnose because we will crash very early in the boot (i.e. >>>> before the call to start_kernel). Auto-detection might be possible >>>> but the performance and code size cost of adding conditional code to >>>> the irqflags macros probably makes it impractical. As such it may >>>> never be possible to remove this limitation (although it might be >>>> possible to find a way to survive long enough to panic and show the >>>> results on the console). >>> >>> This can (and should) be done via patching -- otherwise we risk breaking >>> single kernel image for GICv2+v3. >> >> Do you mean real patching (hunting down all those inlines and >> rewrite them) or simply implementing irqflags with an ops table? If >> the former I didn't look at this because I didn't release we could >> do that... > > A generic patching framework was introduced by Andre Przywara in this > patch: > > e039ee4 arm64: add alternative runtime patching > > I believe you should be able to use this to patch between DAIF and > ICC_PMR accesses. > > You should be able to find examples of this framework being used by > grepping. I've not played with it myself yet.
To follow-up on this, I have a few patches queued that use the runtime patching code to deal with GICv3 in KVM: http://thread.gmane.org/gmane.comp.emulators.kvm.arm.devel/616 The first few patches are already queued for v4.1, and the rest should follow shortly after. Cheers, M. -- Jazz is not dead. It just smells funny... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
