[PATCH v4 15/17] KVM: arm64: Reject hyp trace descriptors with fewer CPUs than hyp_nr_cpus

While a trace descriptor with fewer CPUs than hyp_nr_cpus currently
causes no functional issue, such a configuration is invalid and would
cause the hypervisor to skip ring buffer initialization when allocating
backing pages in EL2.

Enforce nr_cpus == hyp_nr_cpus during trace descriptor validation to
guarantee that every possible CPU has a valid ring buffer descriptor.

Reviewed-by: Fuad Tabba <[email protected]>
Tested-by: Fuad Tabba <[email protected]>
Signed-off-by: Vincent Donnefort <[email protected]>

diff --git a/arch/arm64/kvm/hyp/nvhe/trace.c b/arch/arm64/kvm/hyp/nvhe/trace.c
index e7e150ab265f..6e716295247a 100644
--- a/arch/arm64/kvm/hyp/nvhe/trace.c
+++ b/arch/arm64/kvm/hyp/nvhe/trace.c
@@ -181,6 +181,9 @@ static bool hyp_trace_desc_is_valid(struct hyp_trace_desc *desc, size_t desc_siz
 	desc_end = (void *)desc + desc_size;
 	nr_bpages = desc->bpages_backing_size / sizeof(struct simple_buffer_page);
 
+	if (desc->trace_buffer_desc.nr_cpus != hyp_nr_cpus)
+		return false;
+
 	for_each_ring_buffer_desc(rb_desc, cpu, &desc->trace_buffer_desc) {
 		/* Can we read nr_page_va? */
 		if ((void *)rb_desc + struct_size(rb_desc, page_va, 0) > desc_end)
-- 
2.55.0.508.g3f0d502094-goog