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

From: Marc Zyngier <maz@kernel.org>
To: Kalesh Singh <kaleshsingh@google.com>
Cc: mark.rutland@arm.com, broonie@kernel.org,
	madvenka@linux.microsoft.com, will@kernel.org,
	qperret@google.com, tabba@google.com, james.morse@arm.com,
	alexandru.elisei@arm.com, suzuki.poulose@arm.com,
	catalin.marinas@arm.com, andreyknvl@gmail.com,
	russell.king@oracle.com, vincenzo.frascino@arm.com,
	mhiramat@kernel.org, ast@kernel.org, wangkefeng.wang@huawei.com,
	elver@google.com, keirf@google.com, yuzenghui@huawei.com,
	ardb@kernel.org, oupton@google.com,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
	kernel-team@android.com
Subject: Re: [PATCH v4 11/18] KVM: arm64: Stub implementation of non-protected nVHE HYP stack unwinder
Date: Mon, 18 Jul 2022 08:30:51 +0100	[thread overview]
Message-ID: <877d4a513o.wl-maz@kernel.org> (raw)
In-Reply-To: <20220715061027.1612149-12-kaleshsingh@google.com>

On Fri, 15 Jul 2022 07:10:20 +0100,
Kalesh Singh <kaleshsingh@google.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@google.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.

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