| Message ID | 20171215155101.23505-8-james.morse@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi, On 15/12/17 15:50, James Morse wrote: > Non-VHE systems take an exception to EL2 in order to world-switch into the > guest. When returning from the guest KVM implicitly restores the DAIF > flags when it returns to the kernel at EL1. > > With VHE none of this exception-level jumping happens, so KVMs > world-switch code is exposed to the host kernel's DAIF values, and KVM > spills the guest-exit DAIF values back into the host kernel. > On entry to a guest we have Debug and SError exceptions unmasked, KVM > has switched VBAR but isn't prepared to handle these. On guest exit > Debug exceptions are left disabled once we return to the host and will > stay this way until we enter user space. > > Add a helper to mask/unmask DAIF around VHE guests. The unmask can only > happen after the hosts VBAR value has been synchronised by the isb in > __vhe_hyp_call (via kvm_call_hyp()). Masking could be as late as > setting KVMs VBAR value, but is kept here for symmetry. > > Signed-off-by: James Morse <james.morse@arm.com> > --- > This isn't backportable because of the 'daif' helpers, I will produce a > backport once its merged. > > Changes since v4: > * Added empty declarations for 32bit. (how did I miss that?) v4 of this patch had a Reviewed-by Christoffer, which I didn't pick up as I then went on to confuse everyone... https://patchwork.kernel.org/patch/10017467/ (Sorry Christoffer!) Thanks, James
diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h index a9f7d3f47134..b86fc4162539 100644 --- a/arch/arm/include/asm/kvm_host.h +++ b/arch/arm/include/asm/kvm_host.h @@ -301,4 +301,6 @@ int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu, /* All host FP/SIMD state is restored on guest exit, so nothing to save: */ static inline void kvm_fpsimd_flush_cpu_state(void) {} +static inline void kvm_arm_vhe_guest_enter(void) {} +static inline void kvm_arm_vhe_guest_exit(void) {} #endif /* __ARM_KVM_HOST_H__ */ diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index ea6cb5b24258..4a4764630d98 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -25,6 +25,7 @@ #include <linux/types.h> #include <linux/kvm_types.h> #include <asm/cpufeature.h> +#include <asm/daifflags.h> #include <asm/fpsimd.h> #include <asm/kvm.h> #include <asm/kvm_asm.h> @@ -396,4 +397,13 @@ static inline void kvm_fpsimd_flush_cpu_state(void) sve_flush_cpu_state(); } +static inline void kvm_arm_vhe_guest_enter(void) +{ + local_daif_mask(); +} + +static inline void kvm_arm_vhe_guest_exit(void) +{ + local_daif_restore(DAIF_PROCCTX_NOIRQ); +} #endif /* __ARM64_KVM_HOST_H__ */ diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c index 6b60c98a6e22..86059a478a0a 100644 --- a/virt/kvm/arm/arm.c +++ b/virt/kvm/arm/arm.c @@ -704,9 +704,13 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) */ trace_kvm_entry(*vcpu_pc(vcpu)); guest_enter_irqoff(); + if (has_vhe()) + kvm_arm_vhe_guest_enter(); ret = kvm_call_hyp(__kvm_vcpu_run, vcpu); + if (has_vhe()) + kvm_arm_vhe_guest_exit(); vcpu->mode = OUTSIDE_GUEST_MODE; vcpu->stat.exits++; /*
Non-VHE systems take an exception to EL2 in order to world-switch into the guest. When returning from the guest KVM implicitly restores the DAIF flags when it returns to the kernel at EL1. With VHE none of this exception-level jumping happens, so KVMs world-switch code is exposed to the host kernel's DAIF values, and KVM spills the guest-exit DAIF values back into the host kernel. On entry to a guest we have Debug and SError exceptions unmasked, KVM has switched VBAR but isn't prepared to handle these. On guest exit Debug exceptions are left disabled once we return to the host and will stay this way until we enter user space. Add a helper to mask/unmask DAIF around VHE guests. The unmask can only happen after the hosts VBAR value has been synchronised by the isb in __vhe_hyp_call (via kvm_call_hyp()). Masking could be as late as setting KVMs VBAR value, but is kept here for symmetry. Signed-off-by: James Morse <james.morse@arm.com> --- This isn't backportable because of the 'daif' helpers, I will produce a backport once its merged. Changes since v4: * Added empty declarations for 32bit. (how did I miss that?) arch/arm/include/asm/kvm_host.h | 2 ++ arch/arm64/include/asm/kvm_host.h | 10 ++++++++++ virt/kvm/arm/arm.c | 4 ++++ 3 files changed, 16 insertions(+)