2020-01-09 21:04:22

by Barret Rhoden

Subject: [PATCH] KVM: squelch uninitialized variable warning

If gfn_to_hva_many() fails, __kvm_gfn_to_hva_cache_init() will return an
error. Before it does, it might use nr_pages_avail, which my compiler
complained about:

virt/kvm/kvm_main.c:2193:13: warning: 'nr_pages_avail' may be
used uninitialized in this function [-Wmaybe-uninitialized]

start_gfn += nr_pages_avail;

Signed-off-by: Barret Rhoden <[email protected]>
---
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 d9aced677ddd..f8249b153d33 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2172,7 +2172,7 @@ 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;
int r = start_gfn <= end_gfn ? 0 : -EINVAL;

ghc->gpa = gpa;
--
2.25.0.rc1.283.g88dfdc4193-goog

2020-01-09 22:05:33

by Sean Christopherson

Subject: Re: [PATCH] KVM: squelch uninitialized variable warning

On Thu, Jan 09, 2020 at 02:58:55PM -0500, Barret Rhoden wrote:
> If gfn_to_hva_many() fails, __kvm_gfn_to_hva_cache_init() will return an
> error. Before it does, it might use nr_pages_avail, which my compiler
> complained about:
>
> virt/kvm/kvm_main.c:2193:13: warning: 'nr_pages_avail' may be
> used uninitialized in this function [-Wmaybe-uninitialized]
>
> start_gfn += nr_pages_avail;

Ugh, this whole flow is funky. The change is correct, and is certainly the
minimal change if we want to backport this to stable, but IMO it's putting
lipstick on a pig. I'd rather fix the underlying issues and make the code
more readable in the process. I'll send a patch.

If we want to take this as a minimal fix,

Reviewed-by: Sean Christopherson <[email protected]>

> Signed-off-by: Barret Rhoden <[email protected]>
> ---
> 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 d9aced677ddd..f8249b153d33 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2172,7 +2172,7 @@ 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;
> int r = start_gfn <= end_gfn ? 0 : -EINVAL;
>
> ghc->gpa = gpa;
> --
> 2.25.0.rc1.283.g88dfdc4193-goog
>

2020-01-18 20:21:15

by Paolo Bonzini

Subject: Re: [PATCH] KVM: squelch uninitialized variable warning

On 09/01/20 23:04, Sean Christopherson wrote:
> Reviewed-by: Sean Christopherson <[email protected]>

Thanks, I queued it so that at least it gets to stable.

Paolo