2021-09-19 07:54:47

by Len Baker

Subject: [PATCH] KVM: PPC: Replace zero-length array with flexible array member

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use "flexible array members" [1] for these cases. The
older style of one-element or zero-length arrays should no longer be
used[2].

Also, make use of the struct_size() helper in kzalloc().

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays

Signed-off-by: Len Baker <[email protected]>
---
arch/powerpc/include/asm/kvm_host.h | 2 +-
arch/powerpc/kvm/book3s_64_vio.c | 3 +--
2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 080a7feb7731..3aed653373a5 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -190,7 +190,7 @@ struct kvmppc_spapr_tce_table {
u64 size; /* window size in pages */
struct list_head iommu_tables;
struct mutex alloc_lock;
- struct page *pages[0];
+ struct page *pages[];
};

/* XICS components, defined in book3s_xics.c */
diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
index 6365087f3160..d42b4b6d4a79 100644
--- a/arch/powerpc/kvm/book3s_64_vio.c
+++ b/arch/powerpc/kvm/book3s_64_vio.c
@@ -295,8 +295,7 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
return ret;

ret = -ENOMEM;
- stt = kzalloc(sizeof(*stt) + npages * sizeof(struct page *),
- GFP_KERNEL);
+ stt = kzalloc(struct_size(stt, pages, npages), GFP_KERNEL);
if (!stt)
goto fail_acct;

--
2.25.1

2021-09-21 03:49:17

by Gustavo A. R. Silva

Subject: Re: [PATCH] KVM: PPC: Replace zero-length array with flexible array member

On 9/18/21 09:21, Len Baker wrote:
> There is a regular need in the kernel to provide a way to declare having
> a dynamically sized set of trailing elements in a structure. Kernel code
> should always use "flexible array members" [1] for these cases. The
> older style of one-element or zero-length arrays should no longer be
> used[2].
>
> Also, make use of the struct_size() helper in kzalloc().
>
> [1] https://en.wikipedia.org/wiki/Flexible_array_member
> [2] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays
>
> Signed-off-by: Len Baker <[email protected]>

Reviewed-by: Gustavo A. R. Silva <[email protected]>

Thanks
--
Gustavo

> ---
> arch/powerpc/include/asm/kvm_host.h | 2 +-
> arch/powerpc/kvm/book3s_64_vio.c | 3 +--
> 2 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
> index 080a7feb7731..3aed653373a5 100644
> --- a/arch/powerpc/include/asm/kvm_host.h
> +++ b/arch/powerpc/include/asm/kvm_host.h
> @@ -190,7 +190,7 @@ struct kvmppc_spapr_tce_table {
> u64 size; /* window size in pages */
> struct list_head iommu_tables;
> struct mutex alloc_lock;
> - struct page *pages[0];
> + struct page *pages[];
> };
>
> /* XICS components, defined in book3s_xics.c */
> diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
> index 6365087f3160..d42b4b6d4a79 100644
> --- a/arch/powerpc/kvm/book3s_64_vio.c
> +++ b/arch/powerpc/kvm/book3s_64_vio.c
> @@ -295,8 +295,7 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
> return ret;
>
> ret = -ENOMEM;
> - stt = kzalloc(sizeof(*stt) + npages * sizeof(struct page *),
> - GFP_KERNEL);
> + stt = kzalloc(struct_size(stt, pages, npages), GFP_KERNEL);
> if (!stt)
> goto fail_acct;
>
> --
> 2.25.1
>

2021-10-20 23:25:19

by Gustavo A. R. Silva

Subject: Re: [PATCH] KVM: PPC: Replace zero-length array with flexible array member

On Mon, Sep 20, 2021 at 07:05:07PM -0500, Gustavo A. R. Silva wrote:
>
>
> On 9/18/21 09:21, Len Baker wrote:
> > There is a regular need in the kernel to provide a way to declare having
> > a dynamically sized set of trailing elements in a structure. Kernel code
> > should always use "flexible array members" [1] for these cases. The
> > older style of one-element or zero-length arrays should no longer be
> > used[2].
> >
> > Also, make use of the struct_size() helper in kzalloc().
> >
> > [1] https://en.wikipedia.org/wiki/Flexible_array_member
> > [2] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays
> >
> > Signed-off-by: Len Baker <[email protected]>
>
> Reviewed-by: Gustavo A. R. Silva <[email protected]>

I'm taking this in my -next tree.

Thanks
--
Gustavo