On 28/11/16 16:43, Jintack Lim wrote: > From: Jintack <jintack@xxxxxxxxxxxxxxx> > > Bit positions of CNTHCTL_EL2 are changing depending on HCR_EL2.E2H bit. > EL1PCEN and EL1PCTEN are 1st and 0th bits when E2H is not set, but they > are 11th and 10th bits respectively when E2H is set. Current code is > unintentionally setting wrong bits to CNTHCTL_EL2 with E2H set. > > In fact, we don't need to set those two bits, which allow EL1 and EL0 to > access physical timer and counter respectively, if E2H and TGE are set > for the host kernel. They will be configured later as necessary. First, > we don't need to configure those bits for EL1, since the host kernel > runs in EL2. It is a hypervisor's responsibility to configure them > before entering a VM, which runs in EL0 and EL1. Second, EL0 accesses > are configured in the later stage of boot process. > > Signed-off-by: Jintack Lim <jintack@xxxxxxxxxxxxxxx> > --- > arch/arm64/kernel/head.S | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S > index 332e331..bc3d2db 100644 > --- a/arch/arm64/kernel/head.S > +++ b/arch/arm64/kernel/head.S > @@ -524,10 +524,16 @@ set_hcr: > msr hcr_el2, x0 > isb > > - /* Generic timers. */ > + /* > + * Allow Non-secure EL1 and EL0 to access physical timer and counter. > + * This is not necessary for VHE, since the host kernel runs in EL2, > + * and EL0 accesses are configured in the later stage of boot process. > + */ > + cbnz x2, 1f > mrs x0, cnthctl_el2 > orr x0, x0, #3 // Enable EL1 physical timers > msr cnthctl_el2, x0 > +1: > msr cntvoff_el2, xzr // Clear virtual offset > > #ifdef CONFIG_ARM_GIC_V3 > Nice catch. It may be worth documenting that when HCR_EL2.E2H == 1, CNTHCTL_EL2 has the same bit layout as CNTKCTL_EL1, allowing the kernel designed to run at EL1 to transparently mess with the EL0 bits (as CNTHCTL_EL2 and CNTKCTL_EL1 are the same register in this configuration). Acked-by: Marc Zyngier <marc.zyngier@xxxxxxx> Thanks, M. -- Jazz is not dead. It just smells funny... -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
