KVM: x86: Add helper to query if variable MTRR MSR is base (versus mask)

Add a helper to query whether a variable MTRR MSR is a base versus as mask
MSR.  Replace the unnecessarily complex math with a simple check on bit 0;
base MSRs are even, mask MSRs are odd.

Link: https://lore.kernel.org/r/20230511233351.635053-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
index 9fac1ec..f65ce4b 100644 (file)
--- a/arch/x86/kvm/mtrr.c
+++ b/arch/x86/kvm/mtrr.c
@@ -25,6 +25,12 @@
 #define IA32_MTRR_DEF_TYPE_FE          (1ULL << 10)
 #define IA32_MTRR_DEF_TYPE_TYPE_MASK   (0xff)
 
+static bool is_mtrr_base_msr(unsigned int msr)
+{
+       /* MTRR base MSRs use even numbers, masks use odd numbers. */
+       return !(msr & 0x1);
+}
+
 static bool msr_mtrr_valid(unsigned msr)
 {
        switch (msr) {
@@ -342,10 +348,9 @@ static void set_var_mtrr_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 {
        struct kvm_mtrr *mtrr_state = &vcpu->arch.mtrr_state;
        struct kvm_mtrr_range *tmp, *cur;
-       int index, is_mtrr_mask;
+       int index;
 
        index = (msr - 0x200) / 2;
-       is_mtrr_mask = msr - 0x200 - 2 * index;
        cur = &mtrr_state->var_ranges[index];
 
        /* remove the entry if it's in the list. */
@@ -356,7 +361,7 @@ static void set_var_mtrr_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data)
         * Set all illegal GPA bits in the mask, since those bits must
         * implicitly be 0.  The bits are then cleared when reading them.
         */
-       if (!is_mtrr_mask)
+       if (is_mtrr_base_msr(msr))
                cur->base = data;
        else
                cur->mask = data | kvm_vcpu_reserved_gpa_bits_raw(vcpu);
@@ -418,11 +423,8 @@ int kvm_mtrr_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
        else if (msr == MSR_IA32_CR_PAT)
                *pdata = vcpu->arch.pat;
        else {  /* Variable MTRRs */
-               int is_mtrr_mask;
-
                index = (msr - 0x200) / 2;
-               is_mtrr_mask = msr - 0x200 - 2 * index;
-               if (!is_mtrr_mask)
+               if (is_mtrr_base_msr(msr))
                        *pdata = vcpu->arch.mtrr_state.var_ranges[index].base;
                else
                        *pdata = vcpu->arch.mtrr_state.var_ranges[index].mask;