Re: [PATCH v3] KVM: arm/arm64: Access CNTHCTL_EL2 bit fields correctly

Christoffer Dall
2016-12-06T12:12:21Z

On Tue, Dec 06, 2016 at 11:17:40AM +0000, Marc Zyngier wrote:
> On 01/12/16 19:32, Jintack Lim wrote:
> > Current KVM world switch code is unintentionally setting wrong bits to
> > CNTHCTL_EL2 when E2H == 1, which may allow guest OS to access physical
> > timer. 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.
> >
> > In fact, on VHE we only need to set those bits once, not for every world
> > switch. This is because the host kernel runs in EL2 with HCR_EL2.TGE ==
> > 1, which makes those bits have no effect for the host kernel execution.
> > So we just set those bits once for guests, and that's it.
> >
> > Signed-off-by: Jintack Lim <jintack@cs.columbia.edu>
> > ---
> > v2->v3:
> > - Perform the initialization including CPU hotplug case.
> > - Move has_vhe() to asm/virt.h
> >
> > v1->v2:
> > - Skip configuring cnthctl_el2 in world switch path on VHE system.
> > - Write patch based on linux-next.
> > ---
> > arch/arm/include/asm/virt.h | 5 +++++
> > arch/arm/kvm/arm.c | 3 +++
> > arch/arm64/include/asm/virt.h | 10 ++++++++++
> > include/kvm/arm_arch_timer.h | 1 +
> > virt/kvm/arm/arch_timer.c | 23 +++++++++++++++++++++++
> > virt/kvm/arm/hyp/timer-sr.c | 33 +++++++++++++++++++++------------
> > 6 files changed, 63 insertions(+), 12 deletions(-)
> >
> > diff --git a/arch/arm/include/asm/virt.h b/arch/arm/include/asm/virt.h
> > index a2e75b8..6dae195 100644
> > --- a/arch/arm/include/asm/virt.h
> > +++ b/arch/arm/include/asm/virt.h
> > @@ -80,6 +80,11 @@ static inline bool is_kernel_in_hyp_mode(void)
> > return false;
> > }
> >
> > +static inline bool has_vhe(void)
> > +{
> > + return false;
> > +}
> > +
> > /* The section containing the hypervisor idmap text */
> > extern char __hyp_idmap_text_start[];
> > extern char __hyp_idmap_text_end[];
> > diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> > index 8f92efa..13e54e8 100644
> > --- a/arch/arm/kvm/arm.c
> > +++ b/arch/arm/kvm/arm.c
> > @@ -1099,6 +1099,9 @@ static void cpu_init_hyp_mode(void *dummy)
> > __cpu_init_hyp_mode(pgd_ptr, hyp_stack_ptr, vector_ptr);
> > __cpu_init_stage2();
> >
> > + if (is_kernel_in_hyp_mode())
> > + kvm_timer_init_vhe();
> > +
> > kvm_arm_init_debug();
> > }
> >
> > diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
> > index fea1073..b043cfd 100644
> > --- a/arch/arm64/include/asm/virt.h
> > +++ b/arch/arm64/include/asm/virt.h
> > @@ -47,6 +47,7 @@
> > #include <asm/ptrace.h>
> > #include <asm/sections.h>
> > #include <asm/sysreg.h>
> > +#include <asm/cpufeature.h>
> >
> > /*
> > * __boot_cpu_mode records what mode CPUs were booted in.
> > @@ -80,6 +81,15 @@ static inline bool is_kernel_in_hyp_mode(void)
> > return read_sysreg(CurrentEL) == CurrentEL_EL2;
> > }
> >
> > +static inline bool has_vhe(void)
> > +{
> > +#ifdef CONFIG_ARM64_VHE
>
> Is there a particular reason why this should be guarded by a #ifdef? All
> the symbols should always be available, and since this is a static key,
> the overhead should be really insignificant (provided that you use a
> non-prehistoric compiler...).
>

Isn't this code called from a file shared between 32-bit arm and arm64?
Does the cpus_have_const_cap work on ARM64?

-Christoffer