On Thu, Jun 16, 2022, Paolo Bonzini wrote:
> 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@xxxxxxxxxx>
> > ---
> > 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;"...
That was my guess too, but IIRC I tried the old code with older compilers (gcc-7)
and couldn't trigger any warning. So AFAICT, it was pure paranoia.
