* [PATCH] KVM: x86/mmu: Use boolean returns for (S)PTE accessors
@ 2021-01-23 0:30 Sean Christopherson
2021-01-25 17:24 ` Paolo Bonzini
0 siblings, 1 reply; 2+ messages in thread
From: Sean Christopherson @ 2021-01-23 0:30 UTC (permalink / raw)
To: Paolo Bonzini
Cc: Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel, kvm, linux-kernel
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)
--
2.30.0.280.ga3ce27912f-goog
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] KVM: x86/mmu: Use boolean returns for (S)PTE accessors
2021-01-23 0:30 [PATCH] KVM: x86/mmu: Use boolean returns for (S)PTE accessors Sean Christopherson
@ 2021-01-25 17:24 ` Paolo Bonzini
0 siblings, 0 replies; 2+ messages in thread
From: Paolo Bonzini @ 2021-01-25 17:24 UTC (permalink / raw)
To: Sean Christopherson
Cc: Vitaly Kuznetsov, Wanpeng Li, Jim Mattson, Joerg Roedel, kvm,
linux-kernel
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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