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SubjectRe: [PATCH 01/10] KVM: Do not zero initialize 'pfn' in hva_to_pfn()
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On 4/29/22 03:04, Sean Christopherson wrote:
> Drop the unnecessary initialization of the local 'pfn' variable in
> hva_to_pfn(). First and foremost, '0' is not an invalid pfn, it's a
> perfectly valid pfn on most architectures. I.e. if hva_to_pfn() were to
> return an "uninitializd" pfn, it would actually be interpeted as a legal
> pfn by most callers.
>
> Second, hva_to_pfn() can't return an uninitialized pfn as hva_to_pfn()
> explicitly sets pfn to an error value (or returns an error value directly)
> if a helper returns failure, and all helpers set the pfn on success.
>
> Note, the zeroing of 'pfn' was introduced by commit 2fc843117d64 ("KVM:
> reorganize hva_to_pfn"), and was unnecessary and misguided paranoia even
> then.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> virt/kvm/kvm_main.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 0848430f36c6..04ed4334473c 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2567,7 +2567,7 @@ kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
> bool write_fault, bool *writable)
> {
> struct vm_area_struct *vma;
> - kvm_pfn_t pfn = 0;
> + kvm_pfn_t pfn;
> int npages, r;
>
> /* we can do it either atomically or asynchronously, not both */

I wonder if it was needed to avoid uninitialized variable warnings on
"return pfn;"...

Paolo

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