linux-kernel - Re: [PATCH v5 16/17] KVM: arm64: Introduce pkvm_dump

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Date:   Thu, 21 Jul 2022 10:59:04 +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 16/17] KVM: arm64: Introduce pkvm_dump_backtrace()

Hi Kalesh,

On Thu, Jul 21, 2022 at 6:58 AM Kalesh Singh <kaleshsingh@...gle.com> wrote:
>
> Dumps the pKVM hypervisor backtrace from EL1 by reading the unwinded
> addresses from the shared stacktrace buffer.
>
> The nVHE hyp backtrace is dumped on hyp_panic(), before panicking the
> host.
>
> Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
> ---
>
> Changes in v5:
>   - Move code out from nvhe.h header to handle_exit.c, per Marc
>   - Fix stacktrace symoblization when CONFIG_RAMDOMIZE_BASE is enabled,
>     per Fuad
>   - Use regular comments instead of doc comments, per Fuad
>
>  arch/arm64/kvm/handle_exit.c | 54 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 54 insertions(+)
>
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index f66c0142b335..ad568da5c7d7 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -318,6 +318,57 @@ void handle_exit_early(struct kvm_vcpu *vcpu, int exception_index)
>                 kvm_handle_guest_serror(vcpu, kvm_vcpu_get_esr(vcpu));
>  }
>
> +#ifdef CONFIG_PROTECTED_NVHE_STACKTRACE
> +DECLARE_KVM_NVHE_PER_CPU(unsigned long [NVHE_STACKTRACE_SIZE/sizeof(long)],
> +                        pkvm_stacktrace);
> +
> +/*
> + * pkvm_dump_backtrace - Dump the protected nVHE HYP backtrace.
> + *
> + * @hyp_offset: hypervisor offset, used for address translation.
> + *
> + * Dumping of the pKVM HYP backtrace is done by reading the
> + * stack addresses from the shared stacktrace buffer, since the
> + * host cannot direclty access hyperviosr memory in protected

directly and hypervisor

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

Cheers,
/fuad


> + * mode.
> + */
> +static void pkvm_dump_backtrace(unsigned long hyp_offset)
> +{
> +       unsigned long *stacktrace_entry
> +               = (unsigned long *)this_cpu_ptr_nvhe_sym(pkvm_stacktrace);
> +       unsigned long va_mask, pc;
> +
> +       va_mask = GENMASK_ULL(vabits_actual - 1, 0);
> +
> +       kvm_err("Protected nVHE HYP call trace:\n");
> +
> +       /* The stack trace is terminated by a null entry */
> +       for (; *stacktrace_entry; stacktrace_entry++) {
> +               /* Mask tags and convert to kern addr */
> +               pc = (*stacktrace_entry & va_mask) + hyp_offset;
> +               kvm_err(" [<%016lx>] %pB\n", pc, (void *)(pc + kaslr_offset()));
> +       }
> +
> +       kvm_err("---- End of Protected nVHE HYP call trace ----\n");
> +}
> +#else  /* !CONFIG_PROTECTED_NVHE_STACKTRACE */
> +static void pkvm_dump_backtrace(unsigned long hyp_offset)
> +{
> +       kvm_err("Cannot dump pKVM nVHE stacktrace: !CONFIG_PROTECTED_NVHE_STACKTRACE\n");
> +}
> +#endif /* CONFIG_PROTECTED_NVHE_STACKTRACE */
> +
> +/*
> + * kvm_nvhe_dump_backtrace - Dump KVM nVHE hypervisor backtrace.
> + *
> + * @hyp_offset: hypervisor offset, used for address translation.
> + */
> +static void kvm_nvhe_dump_backtrace(unsigned long hyp_offset)
> +{
> +       if (is_protected_kvm_enabled())
> +               pkvm_dump_backtrace(hyp_offset);
> +}
> +
>  void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
>                                               u64 elr_virt, u64 elr_phys,
>                                               u64 par, uintptr_t vcpu,
> @@ -353,6 +404,9 @@ void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
>                                 (void *)panic_addr);
>         }
>
> +       /* Dump the nVHE hypervisor backtrace */
> +       kvm_nvhe_dump_backtrace(hyp_offset);
> +
>         /*
>          * Hyp has panicked and we're going to handle that by panicking the
>          * kernel. The kernel offset will be revealed in the panic so we're
> --
> 2.37.0.170.g444d1eabd0-goog
>