selftests: kvm: set rax before vmcall

stable inclusion
from stable-v5.10.137
commit c0ba87f3e7b4bc5a4b8c3f132a9c63d594c4af21
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60PLB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c0ba87f3e7b4bc5a4b8c3f132a9c63d594c4af21

--------------------------------

[ Upstream commit 281106f9 ]

kvm_hypercall has to place the hypercall number in rax.

Trace events show that kvm_pv_test doesn't work properly:
     kvm_pv_test-53132: kvm_hypercall: nr 0x0 a0 0x0 a1 0x0 a2 0x0 a3 0x0
     kvm_pv_test-53132: kvm_hypercall: nr 0x0 a0 0x0 a1 0x0 a2 0x0 a3 0x0
     kvm_pv_test-53132: kvm_hypercall: nr 0x0 a0 0x0 a1 0x0 a2 0x0 a3 0x0

With this change, it starts working as expected:
     kvm_pv_test-54285: kvm_hypercall: nr 0x5 a0 0x0 a1 0x0 a2 0x0 a3 0x0
     kvm_pv_test-54285: kvm_hypercall: nr 0xa a0 0x0 a1 0x0 a2 0x0 a3 0x0
     kvm_pv_test-54285: kvm_hypercall: nr 0xb a0 0x0 a1 0x0 a2 0x0 a3 0x0
Signed-off-by: NAndrei Vagin <avagin@google.com>
Message-Id: <20220722230241.1944655-5-avagin@google.com>
Fixes: ac4a4d6d ("selftests: kvm: test enforcement of paravirtual cpuid features")
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>

tools/testing/selftests/kvm/lib/x86_64/processor.c

@@ -1253,6 +1253,6 @@ uint64_t kvm_hypercall(uint64_t nr, uint64_t a0, uint64_t a1, uint64_t a2,
 
 	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;
 }