On Fri, Jul 21, 2017 at 06:15:26PM +0100, Marc Zyngier wrote: > It is an unfortunate situation that CNTFRQ{,_EL0} is often > misprogrammed from the firmware side, leaving it up to the kernel to > work around it. This is usually done by providing an alternative > frequency in the Device Tree. > > Unfortunately, CNTFRQ is accessible from EL0, giving userspace the > wrong frequency, and potentially a different frequency per CPU, which > is definitely not what you want. A possible workaround is to trap this > into the kernel and to emulate it (together with the VDSO being > disabled), and this is what this series is achieving.
Which userspace is actually affected by a broken CNTFRQ register? I suspect most users will be more upset at losing their (perfectly functional) vDSO acceleration than they are about having a broken CNTFRQ value that is hardly ever used, especially since this affects quite a few systems. Will