Re: [PATCH 03/11] KVM: arm64: Change hyp_panic()s dependency on tpidr_el2

[Christoffer Dall <cdall@linaro.org>]

On Mon, May 15, 2017 at 06:43:51PM +0100, James Morse wrote:
> KVM calls hyp_panic() when anything unexpected happens. This may occur
> while a guest owns the EL1 registers. KVM stashes the vcpu pointer in
> tpidr_el2, which it uses to find the host context in order to restore
> the host EL1 registers before parachuting into the host's panic().
> 
> The host context is a struct kvm_cpu_context allocated in the per-cpu
> area, and mapped to hyp. Given the per-cpu offset for this CPU, this is
> easy to find. Change hyp_panic() to take a pointer to the
> struct kvm_cpu_context. Wrap these calls with an asm function that
> retrieves the struct kvm_cpu_context from the host's per-cpu area.
> 
> Copy the per-cpu offset from the hosts tpidr_el1 into tpidr_el2 during
> kvm init. (Later patches will make this unnecessary for VHE hosts)
> 
> We print out the vcpu pointer as part of the panic message. Add a back
> reference to the 'running vcpu' in the host cpu context to preserve this.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
>  arch/arm64/include/asm/kvm_host.h |  2 ++
>  arch/arm64/kvm/hyp/hyp-entry.S    |  7 +++++++
>  arch/arm64/kvm/hyp/s2-setup.c     |  3 +++
>  arch/arm64/kvm/hyp/switch.c       | 25 +++++++++++++------------
>  4 files changed, 25 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 5e19165c5fa8..1407bfc81e9e 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -188,6 +188,8 @@ struct kvm_cpu_context {
>  		u64 sys_regs[NR_SYS_REGS];
>  		u32 copro[NR_COPRO_REGS];
>  	};
> +
> +	struct kvm_vcpu *__hyp_running_vcpu;
>  };
>  
>  typedef struct kvm_cpu_context kvm_cpu_context_t;
> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
> index fce7cc507e0a..0f83e7e402ad 100644
> --- a/arch/arm64/kvm/hyp/hyp-entry.S
> +++ b/arch/arm64/kvm/hyp/hyp-entry.S
> @@ -163,6 +163,13 @@ ENTRY(__hyp_do_panic)
>  	eret
>  ENDPROC(__hyp_do_panic)
>  
> +ENTRY(__hyp_panic)
> +	ldr	x0, =kvm_host_cpu_state

Why is this guaranteed to give us a valid EL2 address?

> +	mrs	x1, tpidr_el2
> +	add	x0, x0, x1
> +	b	hyp_panic
> +ENDPROC(__hyp_panic)
> +

Thanks,
-Christoffer