On Tue, Feb 18, 2020 at 10:47:56AM -0800, Oliver Upton wrote:
> Particularly draconian compilers warn of a possible uninitialized use of
> the nr_pages_avail variable. Silence this warning by initializing it to
> zero.
Can you check if the warning still exists with commit 6ad1e29fe0ab ("KVM:
Clean up __kvm_gfn_to_hva_cache_init() and its callers")? I'm guessing
(hoping?) the suppression is no longer necessary.
commit 6ad1e29fe0aba843dfffc714fced0ef6a2e19502
Author: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Date: Thu Jan 9 14:58:55 2020 -0500
KVM: Clean up __kvm_gfn_to_hva_cache_init() and its callers
Barret reported a (technically benign) bug where nr_pages_avail can be
accessed without being initialized if gfn_to_hva_many() fails.
virt/kvm/kvm_main.c:2193:13: warning: 'nr_pages_avail' may be
used uninitialized in this function [-Wmaybe-uninitialized]
Rather than simply squashing the warning by initializing nr_pages_avail,
fix the underlying issues by reworking __kvm_gfn_to_hva_cache_init() to
return immediately instead of continuing on. Now that all callers check
the result and/or bail immediately on a bad hva, there's no need to
explicitly nullify the memslot on error.
Reported-by: Barret Rhoden <brho@xxxxxxxxxx>
Fixes: f1b9dd5eb86c ("kvm: Disallow wraparound in kvm_gfn_to_hva_cache_init")
Cc: Jim Mattson <jmattson@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Signed-off-by: Oliver Upton <oupton@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 70f03ce0e5c1..dc8a67ad082d 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2219,7 +2219,7 @@ static int __kvm_gfn_to_hva_cache_init(struct kvm_memslots *slots,
> gfn_t start_gfn = gpa >> PAGE_SHIFT;
> gfn_t end_gfn = (gpa + len - 1) >> PAGE_SHIFT;
> gfn_t nr_pages_needed = end_gfn - start_gfn + 1;
> - gfn_t nr_pages_avail;
> + gfn_t nr_pages_avail = 0;
>
> /* Update ghc->generation before performing any error checks. */
> ghc->generation = slots->generation;
> --
> 2.25.0.265.gbab2e86ba0-goog
>
