linux-kernel - Re: [PATCH v5 11/17] KVM: arm64: Stub implementation of non-protected nVHE HYP stack unwinder

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Message-ID: <CA+EHjTzb9cEAP=p39tbNynymnTXSNVuta74sQp05V1VsFVDaJg@mail.gmail.com>
Date:   Thu, 21 Jul 2022 10:58:13 +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 11/17] KVM: arm64: Stub implementation of non-protected
 nVHE HYP stack unwinder

Hi Kalesh,

On Thu, Jul 21, 2022 at 6:58 AM Kalesh Singh <kaleshsingh@...gle.com> wrote:
>
> Add stub implementations of non-protected nVHE stack unwinder, for
> building. These are implemented later in this series.
>
> Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
> ---

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

Cheers,
/fuad

>
> Changes in v5:
>   - Mark unwind_next() as inline, per Marc
>   - Comment !__KVM_NVHE_HYPERVISOR__ unwinder path, per Marc
>
>  arch/arm64/include/asm/stacktrace/nvhe.h | 26 ++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
>
> diff --git a/arch/arm64/include/asm/stacktrace/nvhe.h b/arch/arm64/include/asm/stacktrace/nvhe.h
> index 80d71932afff..3078501f8e22 100644
> --- a/arch/arm64/include/asm/stacktrace/nvhe.h
> +++ b/arch/arm64/include/asm/stacktrace/nvhe.h
> @@ -8,6 +8,12 @@
>   *      the HYP memory. The stack is unwinded in EL2 and dumped to a shared
>   *      buffer where the host can read and print the stacktrace.
>   *
> + *   2) Non-protected nVHE mode - the host can directly access the
> + *      HYP stack pages and unwind the HYP stack in EL1. This saves having
> + *      to allocate shared buffers for the host to read the unwinded
> + *      stacktrace.
> + *
> + *
>   * Copyright (C) 2022 Google LLC
>   */
>  #ifndef __ASM_STACKTRACE_NVHE_H
> @@ -55,5 +61,25 @@ static inline int notrace unwind_next(struct unwind_state *state)
>  NOKPROBE_SYMBOL(unwind_next);
>  #endif /* CONFIG_PROTECTED_NVHE_STACKTRACE */
>
> +#else  /* !__KVM_NVHE_HYPERVISOR__ */
> +/*
> + * Conventional (non-protected) nVHE HYP stack unwinder
> + *
> + * In non-protected mode, the unwinding is done from kernel proper context
> + * (by the host in EL1).
> + */
> +
> +static inline bool on_overflow_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;
> +}
> +NOKPROBE_SYMBOL(unwind_next);
> +
>  #endif /* __KVM_NVHE_HYPERVISOR__ */
>  #endif /* __ASM_STACKTRACE_NVHE_H */
> --
> 2.37.0.170.g444d1eabd0-goog
>