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

Kalesh Singh
2022-07-22T17:25:30Z

On Fri, Jul 22, 2022 at 4:16 AM Oliver Upton <oliver.upton@linux.dev> wrote:
>
> Hi Kalesh,
>
> On Wed, Jul 20, 2022 at 10:57:27PM -0700, Kalesh Singh wrote:
>
> [...]
>
> > +/*
> > + * 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
> > + * 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");
>
> This and the footer printks should be put in respective helpers to share
> between pKVM and non-pKVM backtrace implementations. I imagine users
> will invariably bake some pattern matching to scrape traces, and it
> should be consistent between both flavors.

Hi Oliver,

Ok will split these out into helpers.

>
> > + /* The stack trace is terminated by a null entry */
> > + for (; *stacktrace_entry; stacktrace_entry++) {
>
> At the point we're dumping the backtrace we know that EL2 has already
> soiled itself, so we shouldn't explicitly depend on it providing NULL
> terminators. I believe this loop should have an explicit range && NULL
> check.

Good point, I'll add the additional checks in the next version,

Thanks,
Kalesh
>
> --
> Thanks,
> Oliver