[PATCH v2 4/4] target/i386: Added Intercept CR0 writes check

[Lara Lazier <laramglazier@gmail.com>]

When the selective CR0 write intercept is set, all writes to bits in
CR0 other than CR0.TS or CR0.MP cause a VMEXIT.

Signed-off-by: Lara Lazier <laramglazier@gmail.com>
---
 target/i386/tcg/sysemu/misc_helper.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/target/i386/tcg/sysemu/misc_helper.c b/target/i386/tcg/sysemu/misc_helper.c
index 0cef2f1a4c..db0d8a9d79 100644
--- a/target/i386/tcg/sysemu/misc_helper.c
+++ b/target/i386/tcg/sysemu/misc_helper.c
@@ -84,6 +84,15 @@ void helper_write_crN(CPUX86State *env, int reg, target_ulong t0)
 {
     switch (reg) {
     case 0:
+        /*
+        * If we reach this point, the CR0 write intercept is disabled.
+        * But we could still exit if the hypervisor has requested the selective
+        * intercept for bits other than TS and MP
+        */
+        if (cpu_svm_has_intercept(env, SVM_EXIT_CR0_SEL_WRITE) &&
+            ((env->cr[0] ^ t0) & ~(CR0_TS_MASK | CR0_MP_MASK))) {
+            cpu_vmexit(env, SVM_EXIT_CR0_SEL_WRITE, 0, GETPC());
+        }
         cpu_x86_update_cr0(env, t0);
         break;
     case 3:
-- 
2.25.1