Re: [PATCH v5 16/17] KVM: arm64: Introduce pkvm_dump_backtrace()

Fuad Tabba
2022-07-21T10:00:05Z

Hi Kalesh,

On Thu, Jul 21, 2022 at 6:58 AM Kalesh Singh <kaleshsingh@google.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@google.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@google.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
>