KVM: selftests: Introduce rdmsr_from_l2() and use it for MSR-Bitmap tests

Hyper-V MSR-Bitmap tests do RDMSR from L2 to exit to L1. While 'evmcs_test'
correctly clobbers all GPRs (which are not preserved), 'hyperv_svm_test'
does not. Introduce a more generic rdmsr_from_l2() to avoid code
duplication and remove hardcoding of MSRs.  Do not put it in common code
because it is really just a selftests bug rather than a processor
feature that requires it.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20221101145426.251680-46-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/x86_64/evmcs_test.c

@@ -30,22 +30,15 @@ static void guest_nmi_handler(struct ex_regs *regs)
 {
 }
 
-/* Exits to L1 destroy GRPs! */
-static inline void rdmsr_fs_base(void)
+static inline void rdmsr_from_l2(uint32_t msr)
 {
-	__asm__ __volatile__ ("mov $0xc0000100, %%rcx; rdmsr" : : :
-			      "rax", "rbx", "rcx", "rdx",
-			      "rsi", "rdi", "r8", "r9", "r10", "r11", "r12",
-			      "r13", "r14", "r15");
-}
-static inline void rdmsr_gs_base(void)
-{
-	__asm__ __volatile__ ("mov $0xc0000101, %%rcx; rdmsr" : : :
-			      "rax", "rbx", "rcx", "rdx",
-			      "rsi", "rdi", "r8", "r9", "r10", "r11", "r12",
-			      "r13", "r14", "r15");
+	/* 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");
 }
 
+/* Exit to L1 from L2 with RDMSR instruction */
 void l2_guest_code(void)
 {
 	GUEST_SYNC(7);
@@ -58,11 +51,11 @@ void l2_guest_code(void)
 	vmcall();
 
 	/* MSR-Bitmap tests */
-	rdmsr_fs_base(); /* intercepted */
-	rdmsr_fs_base(); /* intercepted */
-	rdmsr_gs_base(); /* not intercepted */
+	rdmsr_from_l2(MSR_FS_BASE); /* intercepted */
+	rdmsr_from_l2(MSR_FS_BASE); /* intercepted */
+	rdmsr_from_l2(MSR_GS_BASE); /* not intercepted */
 	vmcall();
-	rdmsr_gs_base(); /* intercepted */
+	rdmsr_from_l2(MSR_GS_BASE); /* intercepted */
 
 	/* Done, exit to L1 and never come back.  */
 	vmcall();

tools/testing/selftests/kvm/x86_64/hyperv_svm_test.c

@@ -23,6 +23,15 @@
 
 #define L2_GUEST_STACK_SIZE 256
 
+/* 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)
 {
 	GUEST_SYNC(3);
@@ -30,11 +39,11 @@ void l2_guest_code(void)
 	vmmcall();
 
 	/* MSR-Bitmap tests */
-	rdmsr(MSR_FS_BASE); /* intercepted */
-	rdmsr(MSR_FS_BASE); /* intercepted */
-	rdmsr(MSR_GS_BASE); /* not intercepted */
+	rdmsr_from_l2(MSR_FS_BASE); /* intercepted */
+	rdmsr_from_l2(MSR_FS_BASE); /* intercepted */
+	rdmsr_from_l2(MSR_GS_BASE); /* not intercepted */
 	vmmcall();
-	rdmsr(MSR_GS_BASE); /* intercepted */
+	rdmsr_from_l2(MSR_GS_BASE); /* intercepted */
 
 	GUEST_SYNC(5);