linux-kernel - Re: [PATCH v5 14/17] KVM: arm64: Implement protected nVHE hyp stack unwinder

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Date:   Thu, 21 Jul 2022 10:58:40 +0100
From:   Fuad Tabba <tabba@...gle.com>
To:     Kalesh Singh <kaleshsingh@...gle.com>
Cc:     maz@...nel.org, mark.rutland@....com, broonie@...nel.org,
        madvenka@...ux.microsoft.com, will@...nel.org, qperret@...gle.com,
        james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, catalin.marinas@....com,
        andreyknvl@...il.com, vincenzo.frascino@....com,
        mhiramat@...nel.org, ast@...nel.org, wangkefeng.wang@...wei.com,
        elver@...gle.com, keirf@...gle.com, yuzenghui@...wei.com,
        ardb@...nel.org, oupton@...gle.com,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v5 14/17] KVM: arm64: Implement protected nVHE hyp stack unwinder

Hi Kalesh,

On Thu, Jul 21, 2022 at 6:58 AM Kalesh Singh <kaleshsingh@...gle.com> wrote:
>
> Implements the common framework necessary for unwind() to work in
> the protected nVHE context:
>    - on_accessible_stack()
>    - on_overflow_stack()
>    - unwind_next()
>
> Protected nVHE unwind() is used to unwind and save the hyp stack
> addresses to the shared stacktrace buffer. The host reads the
> entries in this buffer, symbolizes and dumps the stacktrace (later
> patch in the series).
>
> Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
> ---

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

Cheers,
/fuad


>  arch/arm64/include/asm/stacktrace/common.h |  2 ++
>  arch/arm64/include/asm/stacktrace/nvhe.h   | 34 ++++++++++++++++++++--
>  2 files changed, 34 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/stacktrace/common.h b/arch/arm64/include/asm/stacktrace/common.h
> index be7920ba70b0..73fd9e143c4a 100644
> --- a/arch/arm64/include/asm/stacktrace/common.h
> +++ b/arch/arm64/include/asm/stacktrace/common.h
> @@ -34,6 +34,7 @@ enum stack_type {
>         STACK_TYPE_OVERFLOW,
>         STACK_TYPE_SDEI_NORMAL,
>         STACK_TYPE_SDEI_CRITICAL,
> +       STACK_TYPE_HYP,
>         __NR_STACK_TYPES
>  };
>
> @@ -186,6 +187,7 @@ static inline int unwind_next_common(struct unwind_state *state,
>          *
>          * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
>          * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
> +        * HYP -> OVERFLOW
>          *
>          * ... but the nesting itself is strict. Once we transition from one
>          * stack to another, it's never valid to unwind back to that first
> diff --git a/arch/arm64/include/asm/stacktrace/nvhe.h b/arch/arm64/include/asm/stacktrace/nvhe.h
> index 8f02803a005f..c3688e717136 100644
> --- a/arch/arm64/include/asm/stacktrace/nvhe.h
> +++ b/arch/arm64/include/asm/stacktrace/nvhe.h
> @@ -39,10 +39,19 @@ static inline void kvm_nvhe_unwind_init(struct unwind_state *state,
>         state->pc = pc;
>  }
>
> +static inline bool on_hyp_stack(unsigned long sp, unsigned long size,
> +                               struct stack_info *info);
> +
>  static inline bool on_accessible_stack(const struct task_struct *tsk,
>                                        unsigned long sp, unsigned long size,
>                                        struct stack_info *info)
>  {
> +       if (on_accessible_stack_common(tsk, sp, size, info))
> +               return true;
> +
> +       if (on_hyp_stack(sp, size, info))
> +               return true;
> +
>         return false;
>  }
>
> @@ -60,12 +69,27 @@ DECLARE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
>  static inline bool on_overflow_stack(unsigned long sp, unsigned long size,
>                                      struct stack_info *info)
>  {
> -       return false;
> +       unsigned long low = (unsigned long)this_cpu_ptr(overflow_stack);
> +       unsigned long high = low + OVERFLOW_STACK_SIZE;
> +
> +       return on_stack(sp, size, low, high, STACK_TYPE_OVERFLOW, info);
> +}
> +
> +static inline bool on_hyp_stack(unsigned long sp, unsigned long size,
> +                               struct stack_info *info)
> +{
> +       struct kvm_nvhe_init_params *params = this_cpu_ptr(&kvm_init_params);
> +       unsigned long high = params->stack_hyp_va;
> +       unsigned long low = high - PAGE_SIZE;
> +
> +       return on_stack(sp, size, low, high, STACK_TYPE_HYP, info);
>  }
>
>  static inline int notrace unwind_next(struct unwind_state *state)
>  {
> -       return 0;
> +       struct stack_info info;
> +
> +       return unwind_next_common(state, &info, NULL);
>  }
>  NOKPROBE_SYMBOL(unwind_next);
>  #else  /* !CONFIG_PROTECTED_NVHE_STACKTRACE */
> @@ -75,6 +99,12 @@ static inline bool on_overflow_stack(unsigned long sp, unsigned long size,
>         return false;
>  }
>
> +static inline bool on_hyp_stack(unsigned long sp, unsigned long size,
> +                               struct stack_info *info)
> +{
> +       return false;
> +}
> +
>  static inline int notrace unwind_next(struct unwind_state *state)
>  {
>         return 0;
> --
> 2.37.0.170.g444d1eabd0-goog
>