[RFC V3 PATCH 4/6] selftests: kvm: x86: Execute hypercall as per the cpu

[Vishal Annapurve <vannapurve@google.com>]

Add support for executing vmmcall/vmcall instruction on amd/intel cpus.
In general kvm patches the instruction according to the cpu
implementation at runtime. While executing selftest vms from private
memory KVM will not be able to update the private memory of the guest.

Hypercall parameters are fixed to explicitly populate hypercall number
in eax. Otherwise inlined function calls to kvm_hypercall would call
vmmcall/vmcall instruction without updating eax with hypercall number.

Signed-off-by: Vishal Annapurve <vannapurve@google.com>
---
 .../testing/selftests/kvm/lib/x86_64/processor.c  | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
index 53b115876417..09d757a0b148 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
@@ -1254,10 +1254,21 @@ uint64_t kvm_hypercall(uint64_t nr, uint64_t a0, uint64_t a1, uint64_t a2,
 		       uint64_t a3)
 {
 	uint64_t r;
+	static bool is_cpu_checked;
+	static bool is_cpu_amd;
 
-	asm volatile("vmcall"
+	if (!is_cpu_checked)
+		is_cpu_amd = is_amd_cpu();
+
+	if (is_cpu_amd) {
+		asm volatile("vmmcall"
+		     : "=a"(r)
+		     : "a"(nr), "b"(a0), "c"(a1), "d"(a2), "S"(a3));
+	} else {
+		asm volatile("vmcall"
 		     : "=a"(r)
-		     : "b"(a0), "c"(a1), "d"(a2), "S"(a3));
+		     : "a"(nr), "b"(a0), "c"(a1), "d"(a2), "S"(a3));
+	}
 	return r;
 }
 
-- 
2.37.1.595.g718a3a8f04-goog