[PATCH 1/9] KVM: selftests: Add rdmsr_from_l2() implementation in Hyper-V eVMCS test

[Sean Christopherson <seanjc@google.com>]

Add rdmsr_from_l2() in hyperv_evmcs.c, it got left unintentionally omitted
when applying code review feeback on the fly.  Intentionally duplicate
the code that's in hyperv_svm_test.c, the helper really should not exist
(L1 shouldn't clobber GPRs) and will hopefully be removed sooner than
later.  Until that happens, deter other tests from using the somewhat
misleading helper (it doesn't actually read L2's MSR value).

Link: https://lore.kernel.org/all/Y2FFNO3Bu9Z3LtCW@google.com
Fixes: 860e80157068 ("KVM: selftests: Introduce rdmsr_from_l2() and use it for MSR-Bitmap tests")
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 tools/testing/selftests/kvm/x86_64/hyperv_evmcs.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tools/testing/selftests/kvm/x86_64/hyperv_evmcs.c b/tools/testing/selftests/kvm/x86_64/hyperv_evmcs.c
index d418954590b1..ea58e5b436e8 100644
--- a/tools/testing/selftests/kvm/x86_64/hyperv_evmcs.c
+++ b/tools/testing/selftests/kvm/x86_64/hyperv_evmcs.c
@@ -31,6 +31,15 @@ static void guest_nmi_handler(struct ex_regs *regs)
 {
 }
 
+/* Exit to L1 from L2 with RDMSR instruction */
+static inline void rdmsr_from_l2(uint32_t msr)
+{
+	/* Currently, L1 doesn't preserve GPRs during vmexits. */
+	__asm__ __volatile__ ("rdmsr" : : "c"(msr) :
+			      "rax", "rbx", "rdx", "rsi", "rdi", "r8", "r9",
+			      "r10", "r11", "r12", "r13", "r14", "r15");
+}
+
 void l2_guest_code(void)
 {
 	u64 unused;
-- 
2.38.1.584.g0f3c55d4c2-goog