Re: [PATCH v5 13/17] KVM: arm64: Prepare non-protected nVHE hypervisor stacktrace

[Fuad Tabba <tabba@google.com>]

Hi Kalesh,


On Thu, Jul 21, 2022 at 6:58 AM Kalesh Singh <kaleshsingh@google.com> wrote:
>
> In non-protected nVHE mode (non-pKVM) the host can directly access
> hypervisor memory; and unwinding of the hypervisor stacktrace is
> done from EL1 to save on memory for shared buffers.
>
> To unwind the hypervisor stack from EL1 the host needs to know the
> starting point for the unwind and information that will allow it to
> translate hypervisor stack addresses to the corresponding kernel
> addresses. This patch sets up this book keeping. It is made use of
> later in the series.
>
> Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
> ---

Reviewed-by: Fuad Tabba <tabba@google.com>

Cheers,
/fuad


>
> Changes in v5:
>   - Use regular comments instead of doc comments, per Fuad
>
>  arch/arm64/include/asm/kvm_asm.h         | 16 ++++++++++++++++
>  arch/arm64/include/asm/stacktrace/nvhe.h |  4 ++++
>  arch/arm64/kvm/hyp/nvhe/stacktrace.c     | 24 ++++++++++++++++++++++++
>  3 files changed, 44 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index 2e277f2ed671..53035763e48e 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -176,6 +176,22 @@ struct kvm_nvhe_init_params {
>         unsigned long vtcr;
>  };
>
> +/*
> + * Used by the host in EL1 to dump the nVHE hypervisor backtrace on
> + * hyp_panic() in non-protected mode.
> + *
> + * @stack_base:                 hyp VA of the hyp_stack base.
> + * @overflow_stack_base:        hyp VA of the hyp_overflow_stack base.
> + * @fp:                         hyp FP where the backtrace begins.
> + * @pc:                         hyp PC where the backtrace begins.
> + */
> +struct kvm_nvhe_stacktrace_info {
> +       unsigned long stack_base;
> +       unsigned long overflow_stack_base;
> +       unsigned long fp;
> +       unsigned long pc;
> +};
> +
>  /* Translate a kernel address @ptr into its equivalent linear mapping */
>  #define kvm_ksym_ref(ptr)                                              \
>         ({                                                              \
> diff --git a/arch/arm64/include/asm/stacktrace/nvhe.h b/arch/arm64/include/asm/stacktrace/nvhe.h
> index 05d7e03e0a8c..8f02803a005f 100644
> --- a/arch/arm64/include/asm/stacktrace/nvhe.h
> +++ b/arch/arm64/include/asm/stacktrace/nvhe.h
> @@ -19,6 +19,7 @@
>  #ifndef __ASM_STACKTRACE_NVHE_H
>  #define __ASM_STACKTRACE_NVHE_H
>
> +#include <asm/kvm_asm.h>
>  #include <asm/stacktrace/common.h>
>
>  /*
> @@ -52,6 +53,9 @@ static inline bool on_accessible_stack(const struct task_struct *tsk,
>   * In protected mode, the unwinding is done by the hypervisor in EL2.
>   */
>
> +DECLARE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack);
> +DECLARE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
> +
>  #ifdef CONFIG_PROTECTED_NVHE_STACKTRACE
>  static inline bool on_overflow_stack(unsigned long sp, unsigned long size,
>                                      struct stack_info *info)
> diff --git a/arch/arm64/kvm/hyp/nvhe/stacktrace.c b/arch/arm64/kvm/hyp/nvhe/stacktrace.c
> index 60461c033a04..cbd365f4f26a 100644
> --- a/arch/arm64/kvm/hyp/nvhe/stacktrace.c
> +++ b/arch/arm64/kvm/hyp/nvhe/stacktrace.c
> @@ -9,6 +9,28 @@
>  DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack)
>         __aligned(16);
>
> +DEFINE_PER_CPU(struct kvm_nvhe_stacktrace_info, kvm_stacktrace_info);
> +
> +/*
> + * hyp_prepare_backtrace - Prepare non-protected nVHE backtrace.
> + *
> + * @fp : frame pointer at which to start the unwinding.
> + * @pc : program counter at which to start the unwinding.
> + *
> + * Save the information needed by the host to unwind the non-protected
> + * nVHE hypervisor stack in EL1.
> + */
> +static void hyp_prepare_backtrace(unsigned long fp, unsigned long pc)
> +{
> +       struct kvm_nvhe_stacktrace_info *stacktrace_info = this_cpu_ptr(&kvm_stacktrace_info);
> +       struct kvm_nvhe_init_params *params = this_cpu_ptr(&kvm_init_params);
> +
> +       stacktrace_info->stack_base = (unsigned long)(params->stack_hyp_va - PAGE_SIZE);
> +       stacktrace_info->overflow_stack_base = (unsigned long)this_cpu_ptr(overflow_stack);
> +       stacktrace_info->fp = fp;
> +       stacktrace_info->pc = pc;
> +}
> +
>  #ifdef CONFIG_PROTECTED_NVHE_STACKTRACE
>  DEFINE_PER_CPU(unsigned long [NVHE_STACKTRACE_SIZE/sizeof(long)], pkvm_stacktrace);
>
> @@ -89,4 +111,6 @@ void kvm_nvhe_prepare_backtrace(unsigned long fp, unsigned long pc)
>  {
>         if (is_protected_kvm_enabled())
>                 pkvm_save_backtrace(fp, pc);
> +       else
> +               hyp_prepare_backtrace(fp, pc);
>  }
> --
> 2.37.0.170.g444d1eabd0-goog
>