linux-kernel - Re: [PATCH v4 11/18] KVM: arm64: Stub implementation of non-protected nVHE HYP stack unwinder

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Date:   Mon, 18 Jul 2022 08:30:51 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Kalesh Singh <kaleshsingh@...gle.com>
Cc:     mark.rutland@....com, broonie@...nel.org,
        madvenka@...ux.microsoft.com, will@...nel.org, qperret@...gle.com,
        tabba@...gle.com, james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, catalin.marinas@....com,
        andreyknvl@...il.com, russell.king@...cle.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 v4 11/18] KVM: arm64: Stub implementation of non-protected nVHE HYP stack unwinder

On Fri, 15 Jul 2022 07:10:20 +0100,
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>
> ---
>  arch/arm64/include/asm/stacktrace/nvhe.h | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/stacktrace/nvhe.h b/arch/arm64/include/asm/stacktrace/nvhe.h
> index 1eac4e57f2ae..36cf7858ddd8 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
> @@ -53,5 +59,21 @@ static int notrace unwind_next(struct unwind_state *state)
>  NOKPROBE_SYMBOL(unwind_next);
>  #endif	/* CONFIG_PROTECTED_NVHE_STACKTRACE */
>  
> +/*
> + * Non-protected nVHE HYP stack unwinder
> + */
> +#else	/* !__KVM_NVHE_HYPERVISOR__ */

I don't get this path. This either represents the VHE hypervisor or
the kernel proper. Which one is it?

> +static inline bool on_overflow_stack(unsigned long sp, unsigned long size,
> +				     struct stack_info *info)
> +{
> +	return false;
> +}
> +
> +static int notrace unwind_next(struct unwind_state *state)
> +{
> +	return 0;
> +}
> +NOKPROBE_SYMBOL(unwind_next);
> +
>  #endif	/* __KVM_NVHE_HYPERVISOR__ */
>  #endif	/* __ASM_STACKTRACE_NVHE_H */

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.