struct kvm_mmu_role_regs is computed just once and then accessed.  Use
const to make this clearer, even though the const fields of struct
kvm_mmu_role_regs already prevent modifications to the contents of the
struct, or rather make them harder.

Reviewed-by: David Matlack <dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/mmu/mmu.c | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 4f9bbd02fb8b..97566ac539e3 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -197,7 +197,7 @@ struct kvm_mmu_role_regs {
  * the single source of truth for the MMU's state.
  */
 #define BUILD_MMU_ROLE_REGS_ACCESSOR(reg, name, flag)			\
-static inline bool __maybe_unused ____is_##reg##_##name(struct kvm_mmu_role_regs *regs)\
+static inline bool __maybe_unused ____is_##reg##_##name(const struct kvm_mmu_role_regs *regs)\
 {									\
 	return !!(regs->reg & flag);					\
 }
@@ -244,7 +244,7 @@ static struct kvm_mmu_role_regs vcpu_to_role_regs(struct kvm_vcpu *vcpu)
 	return regs;
 }
 
-static int role_regs_to_root_level(struct kvm_mmu_role_regs *regs)
+static int role_regs_to_root_level(const struct kvm_mmu_role_regs *regs)
 {
 	if (!____is_cr0_pg(regs))
 		return 0;
@@ -4681,7 +4681,7 @@ static void paging32_init_context(struct kvm_mmu *context)
 }
 
 static union kvm_mmu_extended_role kvm_calc_mmu_role_ext(struct kvm_vcpu *vcpu,
-							 struct kvm_mmu_role_regs *regs)
+							 const struct kvm_mmu_role_regs *regs)
 {
 	union kvm_mmu_extended_role ext = {0};
 
@@ -4704,7 +4704,7 @@ static union kvm_mmu_extended_role kvm_calc_mmu_role_ext(struct kvm_vcpu *vcpu,
 }
 
 static union kvm_mmu_role kvm_calc_mmu_role_common(struct kvm_vcpu *vcpu,
-						   struct kvm_mmu_role_regs *regs,
+						   const struct kvm_mmu_role_regs *regs,
 						   bool base_only)
 {
 	union kvm_mmu_role role = {0};
@@ -4740,7 +4740,8 @@ static inline int kvm_mmu_get_tdp_level(struct kvm_vcpu *vcpu)
 
 static union kvm_mmu_role
 kvm_calc_tdp_mmu_root_page_role(struct kvm_vcpu *vcpu,
-				struct kvm_mmu_role_regs *regs, bool base_only)
+				const struct kvm_mmu_role_regs *regs,
+				bool base_only)
 {
 	union kvm_mmu_role role = kvm_calc_mmu_role_common(vcpu, regs, base_only);
 
@@ -4786,7 +4787,8 @@ static void init_kvm_tdp_mmu(struct kvm_vcpu *vcpu)
 
 static union kvm_mmu_role
 kvm_calc_shadow_root_page_role_common(struct kvm_vcpu *vcpu,
-				      struct kvm_mmu_role_regs *regs, bool base_only)
+				      const struct kvm_mmu_role_regs *regs,
+				      bool base_only)
 {
 	union kvm_mmu_role role = kvm_calc_mmu_role_common(vcpu, regs, base_only);
 
@@ -4799,7 +4801,8 @@ kvm_calc_shadow_root_page_role_common(struct kvm_vcpu *vcpu,
 
 static union kvm_mmu_role
 kvm_calc_shadow_mmu_root_page_role(struct kvm_vcpu *vcpu,
-				   struct kvm_mmu_role_regs *regs, bool base_only)
+				   const struct kvm_mmu_role_regs *regs,
+				   bool base_only)
 {
 	union kvm_mmu_role role =
 		kvm_calc_shadow_root_page_role_common(vcpu, regs, base_only);
@@ -4817,7 +4820,7 @@ kvm_calc_shadow_mmu_root_page_role(struct kvm_vcpu *vcpu,
 }
 
 static void shadow_mmu_init_context(struct kvm_vcpu *vcpu, struct kvm_mmu *context,
-				    struct kvm_mmu_role_regs *regs,
+				    const struct kvm_mmu_role_regs *regs,
 				    union kvm_mmu_role new_role)
 {
 	if (new_role.as_u64 == context->mmu_role.as_u64)
@@ -4840,7 +4843,7 @@ static void shadow_mmu_init_context(struct kvm_vcpu *vcpu, struct kvm_mmu *conte
 }
 
 static void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu,
-				struct kvm_mmu_role_regs *regs)
+				const struct kvm_mmu_role_regs *regs)
 {
 	struct kvm_mmu *context = &vcpu->arch.root_mmu;
 	union kvm_mmu_role new_role =
@@ -4851,7 +4854,7 @@ static void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu,
 
 static union kvm_mmu_role
 kvm_calc_shadow_npt_root_page_role(struct kvm_vcpu *vcpu,
-				   struct kvm_mmu_role_regs *regs)
+				   const struct kvm_mmu_role_regs *regs)
 {
 	union kvm_mmu_role role =
 		kvm_calc_shadow_root_page_role_common(vcpu, regs, false);
@@ -4951,7 +4954,7 @@ static void init_kvm_softmmu(struct kvm_vcpu *vcpu)
 }
 
 static union kvm_mmu_role
-kvm_calc_nested_mmu_role(struct kvm_vcpu *vcpu, struct kvm_mmu_role_regs *regs)
+kvm_calc_nested_mmu_role(struct kvm_vcpu *vcpu, const struct kvm_mmu_role_regs *regs)
 {
 	union kvm_mmu_role role;
 
-- 
2.31.1

On Mon, Feb 21, 2022, Paolo Bonzini wrote:
> struct kvm_mmu_role_regs is computed just once and then accessed.  Use
> const to make this clearer, even though the const fields of struct
> kvm_mmu_role_regs already prevent modifications to the contents of the
> struct, or rather make them harder.
> 
> Reviewed-by: David Matlack <dmatlack@google.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 25 ++++++++++++++-----------
>  1 file changed, 14 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 4f9bbd02fb8b..97566ac539e3 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -197,7 +197,7 @@ struct kvm_mmu_role_regs {
>   * the single source of truth for the MMU's state.
>   */
>  #define BUILD_MMU_ROLE_REGS_ACCESSOR(reg, name, flag)			\
> -static inline bool __maybe_unused ____is_##reg##_##name(struct kvm_mmu_role_regs *regs)\
> +static inline bool __maybe_unused ____is_##reg##_##name(const struct kvm_mmu_role_regs *regs)\

This is one of the very rare times I think it's worth splitting the prototype,
it's not like the function name is grep-friendly anyways.  Either way,

Reviewed-by: Sean Christopherson <seanjc@google.com>

static inline bool __maybe_unused					\
____is_##reg##_##name(const struct kvm_mmu_role_regs *regs)		\
{									\
	return !!(regs->reg & flag);					\
}