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From:   Fuad Tabba <tabba@google.com>
Date:   Thu, 21 Jul 2022 10:57:56 +0100
Message-ID: <CA+EHjTwvGj+1TQ1OKDNhJsFd=TjwuPr=mjGxvZDqTKWYMcbN+Q@mail.gmail.com>
Subject: Re: [PATCH v5 09/17] KVM: arm64: Allocate shared pKVM hyp stacktrace buffers
To:     Kalesh Singh <kaleshsingh@google.com>
Cc:     maz@kernel.org, mark.rutland@arm.com, broonie@kernel.org,
        madvenka@linux.microsoft.com, will@kernel.org, qperret@google.com,
        james.morse@arm.com, alexandru.elisei@arm.com,
        suzuki.poulose@arm.com, catalin.marinas@arm.com,
        andreyknvl@gmail.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
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Hi Kalesh,

On Thu, Jul 21, 2022 at 6:57 AM Kalesh Singh <kaleshsingh@google.com> wrote:
>
> In protected nVHE mode the host cannot directly access
> hypervisor memory, so we will dump the hypervisor stacktrace
> to a shared buffer with the host.
>
> The minimum size for the buffer required, assuming the min frame
> size of [x29, x30] (2 * sizeof(long)), is half the combined size of
> the hypervisor and overflow stacks plus an additional entry to
> delimit the end of the stacktrace.
>
> The stacktrace buffers are used later in the seried to dump the

nit: seried/series

> nVHE hypervisor stacktrace when using protected-mode.
>
> Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
> ---

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

Cheers,
/fuad


> Changes in v5:
>   - Fix typo in commit text, per Marc
>
>  arch/arm64/include/asm/memory.h      | 8 ++++++++
>  arch/arm64/kvm/hyp/nvhe/stacktrace.c | 4 ++++
>  2 files changed, 12 insertions(+)
>
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index 0af70d9abede..cab80a9a4086 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -113,6 +113,14 @@
>
>  #define OVERFLOW_STACK_SIZE    SZ_4K
>
> +/*
> + * With the minimum frame size of [x29, x30], exactly half the combined
> + * sizes of the hyp and overflow stacks is the maximum size needed to
> + * save the unwinded stacktrace; plus an additional entry to delimit the
> + * end.
> + */
> +#define NVHE_STACKTRACE_SIZE   ((OVERFLOW_STACK_SIZE + PAGE_SIZE) / 2 + sizeof(long))
> +
>  /*
>   * Alignment of kernel segments (e.g. .text, .data).
>   *
> diff --git a/arch/arm64/kvm/hyp/nvhe/stacktrace.c b/arch/arm64/kvm/hyp/nvhe/stacktrace.c
> index a3d5b34e1249..69e65b457f1c 100644
> --- a/arch/arm64/kvm/hyp/nvhe/stacktrace.c
> +++ b/arch/arm64/kvm/hyp/nvhe/stacktrace.c
> @@ -9,3 +9,7 @@
>
>  DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack)
>         __aligned(16);
> +
> +#ifdef CONFIG_PROTECTED_NVHE_STACKTRACE
> +DEFINE_PER_CPU(unsigned long [NVHE_STACKTRACE_SIZE/sizeof(long)], pkvm_stacktrace);
> +#endif /* CONFIG_PROTECTED_NVHE_STACKTRACE */
> --
> 2.37.0.170.g444d1eabd0-goog
>