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

On Fri, Jul 22, 2022 at 4:16 AM Oliver Upton [off-list ref] wrote:

Hi Kalesh,

On Wed, Jul 20, 2022 at 10:57:27PM -0700, Kalesh Singh wrote:

[...]

quoted

+/*
+ * 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.

quoted

+     /* 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

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