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SubjectRe: [PATCH] KVM: x86/mmu: Use boolean returns for (S)PTE accessors
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On 23/01/21 01:30, Sean Christopherson wrote:
> Return a 'bool' instead of an 'int' for various PTE accessors that are
> boolean in nature, e.g. is_shadow_present_pte(). Returning an int is
> goofy and potentially dangerous, e.g. if a flag being checked is moved
> into the upper 32 bits of a SPTE, then the compiler may silently squash
> the entire check since casting to an int is guaranteed to yield a
> return value of '0'.
>
> Opportunistically refactor is_last_spte() so that it naturally returns
> a bool value instead of letting it implicitly cast 0/1 to false/true.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/mmu.h | 2 +-
> arch/x86/kvm/mmu/spte.h | 12 ++++--------
> 2 files changed, 5 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 581925e476d6..f61e18dad2f3 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -145,7 +145,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> *
> * TODO: introduce APIs to split these two cases.
> */
> -static inline int is_writable_pte(unsigned long pte)
> +static inline bool is_writable_pte(unsigned long pte)
> {
> return pte & PT_WRITABLE_MASK;
> }
> diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
> index 2b3a30bd38b0..398fd1bb13a7 100644
> --- a/arch/x86/kvm/mmu/spte.h
> +++ b/arch/x86/kvm/mmu/spte.h
> @@ -185,23 +185,19 @@ static inline bool is_access_track_spte(u64 spte)
> return !spte_ad_enabled(spte) && (spte & shadow_acc_track_mask) == 0;
> }
>
> -static inline int is_shadow_present_pte(u64 pte)
> +static inline bool is_shadow_present_pte(u64 pte)
> {
> return (pte != 0) && !is_mmio_spte(pte);
> }
>
> -static inline int is_large_pte(u64 pte)
> +static inline bool is_large_pte(u64 pte)
> {
> return pte & PT_PAGE_SIZE_MASK;
> }
>
> -static inline int is_last_spte(u64 pte, int level)
> +static inline bool is_last_spte(u64 pte, int level)
> {
> - if (level == PG_LEVEL_4K)
> - return 1;
> - if (is_large_pte(pte))
> - return 1;
> - return 0;
> + return (level == PG_LEVEL_4K) || is_large_pte(pte);
> }
>
> static inline bool is_executable_pte(u64 spte)
>

Queued, thanks.

Paolo

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