[RFC,06/26] KVM: VMX: Add helpers to handle the writes to MSR's R/O and R/WC0 bits

Commit Message

Zhao Liu Feb. 3, 2024, 9:11 a.m. UTC

From: Zhao Liu <[e-mail]>

For WRMSR emulation, any write to R/O bit and any nonzero write to R/WC0
bit must be ignored.

Provide 2 helpers to emulate the above R/O and R/WC0 write behavior.

Tested-by: Yanting Jiang <[e-mail]>
Signed-off-by: Zhao Liu <[e-mail]>
---
 arch/x86/kvm/vmx/vmx.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

Patch

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index e262bc2ba4e5..8f5981635fe5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2147,6 +2147,20 @@  static u64 vmx_get_supported_debugctl(struct kvm_vcpu *vcpu, bool host_initiated
 	return debugctl;
 }
 
+/* Ignore writes to R/O bits. */
+static inline u64 vmx_set_msr_ro_bits(u64 new_val, u64 old_val, u64 ro_mask)
+{
+	return (new_val & ~ro_mask) | (old_val & ro_mask);
+}
+
+/* Ignore non-zero writes to R/WC0 bits. */
+static inline u64 vmx_set_msr_rwc0_bits(u64 new_val, u64 old_val, u64 rwc0_mask)
+{
+	u64 new_rwc0 = new_val & rwc0_mask, old_rwc0 = old_val & rwc0_mask;
+
+	return ((new_rwc0 | ~old_rwc0) & old_rwc0) | (new_val & ~rwc0_mask);
+}
+
 /*
  * Writes msr value into the appropriate "register".
  * Returns 0 on success, non-0 otherwise.