KVM: arm64: Add hyp_printk event to nVHE/pKVM hyp

Create an event to allow developers to log pretty much anything into the
hypervisor tracing buffer with trace_hyp_printk(), just like the kernel
tracing has the function trace_printk().

  #include <asm/kvm_hypevents.h>

  trace_hyp_printk("foobar");
  trace_hyp_printk("foo=%d", foo);
  trace_hyp_printk("foo=%d bar=0x%016llx", foo, bar);

To ensure writing into the tracing buffer is fast, store the string
format into a kernel-accessible ELF section. The hypervisor only has to
write into the event the string ID, which is the delta between the
hyp_string_fmt and the start of the ELF section.

The string format is parsed by the kernel. It is therefore not possible
to dereference hypervisor pointers and the format specifier %s is not
supported. Also the %p specifiers will fail to find the hypervisor
function.

To not waste tracing buffer data, use a dynamic size. Each argument is 8
bytes.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20261001143000.3371786-5-vdonnefort@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

0 files changed, 0 insertions, 0 deletions