KVM: nVMX: Dynamically compute max VMCS index for vmcs12

Calculate the max VMCS index for vmcs12 by walking the array to find the
actual max index.  Hardcoding the index is prone to bitrot, and the
calculation is only done on KVM bringup (albeit on every CPU, but there
aren't _that_ many null entries in the array).

Fixes: 3c0f99366e34 ("KVM: nVMX: Add a TSC multiplier field in VMCS12")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210618214658.2700765-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index b531e08a095bb2e868151a400364a86314154080..183fd9d62fc52b9cc56a1dd39deca88b85c3cd2b 100644 (file)
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -6374,6 +6374,40 @@ void nested_vmx_set_vmcs_shadowing_bitmap(void)
        }
 }
 
+/*
+ * Indexing into the vmcs12 uses the VMCS encoding rotated left by 6.  Undo
+ * that madness to get the encoding for comparison.
+ */
+#define VMCS12_IDX_TO_ENC(idx) ((u16)(((u16)(idx) >> 6) | ((u16)(idx) << 10)))
+
+static u64 nested_vmx_calc_vmcs_enum_msr(void)
+{
+       /*
+        * Note these are the so called "index" of the VMCS field encoding, not
+        * the index into vmcs12.
+        */
+       unsigned int max_idx, idx;
+       int i;
+
+       /*
+        * For better or worse, KVM allows VMREAD/VMWRITE to all fields in
+        * vmcs12, regardless of whether or not the associated feature is
+        * exposed to L1.  Simply find the field with the highest index.
+        */
+       max_idx = 0;
+       for (i = 0; i < nr_vmcs12_fields; i++) {
+               /* The vmcs12 table is very, very sparsely populated. */
+               if (!vmcs_field_to_offset_table[i])
+                       continue;
+
+               idx = vmcs_field_index(VMCS12_IDX_TO_ENC(i));
+               if (idx > max_idx)
+                       max_idx = idx;
+       }
+
+       return (u64)max_idx << VMCS_FIELD_INDEX_SHIFT;
+}
+
 /*
  * nested_vmx_setup_ctls_msrs() sets up variables containing the values to be
  * returned for the various VMX controls MSRs when nested VMX is enabled.
@@ -6619,8 +6653,7 @@ void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, u32 ept_caps)
        rdmsrl(MSR_IA32_VMX_CR0_FIXED1, msrs->cr0_fixed1);
        rdmsrl(MSR_IA32_VMX_CR4_FIXED1, msrs->cr4_fixed1);
 
-       /* highest index: VMX_PREEMPTION_TIMER_VALUE */
-       msrs->vmcs_enum = VMCS12_MAX_FIELD_INDEX << 1;
+       msrs->vmcs_enum = nested_vmx_calc_vmcs_enum_msr();
 }
 
 void nested_vmx_hardware_unsetup(void)

diff --git a/arch/x86/kvm/vmx/vmcs.h b/arch/x86/kvm/vmx/vmcs.h
index 1472c6c376f74a661d053c616f648556019da64a..de3b04d4b587a7e4108a498cde46bd68e05f344c 100644 (file)
--- a/arch/x86/kvm/vmx/vmcs.h
+++ b/arch/x86/kvm/vmx/vmcs.h
@@ -164,4 +164,12 @@ static inline int vmcs_field_readonly(unsigned long field)
        return (((field >> 10) & 0x3) == 1);
 }
 
+#define VMCS_FIELD_INDEX_SHIFT         (1)
+#define VMCS_FIELD_INDEX_MASK          GENMASK(9, 1)
+
+static inline unsigned int vmcs_field_index(unsigned long field)
+{
+       return (field & VMCS_FIELD_INDEX_MASK) >> VMCS_FIELD_INDEX_SHIFT;
+}
+
 #endif /* __KVM_X86_VMX_VMCS_H */

diff --git a/arch/x86/kvm/vmx/vmcs12.h b/arch/x86/kvm/vmx/vmcs12.h
index bb81a23afe89867af41ea39eaf0523063f216423..5e0e1b39f4950896df490651d6dc602e7db8397a 100644 (file)
--- a/arch/x86/kvm/vmx/vmcs12.h
+++ b/arch/x86/kvm/vmx/vmcs12.h
@@ -205,12 +205,6 @@ struct __packed vmcs12 {
  */
 #define VMCS12_SIZE            KVM_STATE_NESTED_VMX_VMCS_SIZE
 
-/*
- * VMCS12_MAX_FIELD_INDEX is the highest index value used in any
- * supported VMCS12 field encoding.
- */
-#define VMCS12_MAX_FIELD_INDEX 0x17
-
 /*
  * For save/restore compatibility, the vmcs12 field offsets must not change.
  */