[PATCH v2 0/5] arm64: kernel: Add support for User Access Override

[Catalin Marinas]

On Fri, Feb 19, 2016 at 03:38:44PM +0000, Peter Maydell wrote:
> On 18 February 2016 at 18:03, Catalin Marinas <catalin.marinas at arm.com> wrote:
> > On Fri, Feb 05, 2016 at 02:58:45PM +0000, James Morse wrote:
> >> James Morse (5):
> >>   arm64: cpufeature: Change read_cpuid() to use sysreg's mrs_s macro
> >>   arm64: add ARMv8.2 id_aa64mmfr2 boiler plate
> >>   arm64: kernel: Add support for User Access Override
> >>   arm64: cpufeature: Test 'matches' pointer to find the end of the list
> >>   arm64: kernel: Don't toggle PAN on systems with UAO
> >
> > Patches applied with an additional fixup on top for removing
> > get_thread_info().
> 
> Just to let you know, unfortunately this series breaks booting the
> kernel on QEMU. We didn't implement the parts of the ID register
> space that the ARM ARM documents as "reserved, RAZ", and so when
> the kernel touches ID_AA64MMFR2 (new in v8.2) QEMU hands it an
> UNDEF. This is obviously a bug in QEMU, and I just sent out a patch
> for it: http://patchwork.ozlabs.org/patch/585237/ -- but of course
> that doesn't do anything for all the buggy QEMUs already in the field.
> 
> This is more of a heads-up than a demand that you Do Something,
> but perhaps somebody has a clever idea...

Only if Qemu had its own MIDR/REVIDR ;) (and patch the instruction like
other errata workarounds).

-- 
Catalin