There's an ongoing effort to remove VLAs[1] from the kernel to eventually
turn on -Wvla. It turns out, the few VLAs in use in Xen produce only a
single entry array that is always bounded by GDT_SIZE. Clean up the code to
get rid of the VLA and the loop.
[1] https://lkml.org/lkml/2018/3/7/621
Signed-off-by: Laura Abbott <[email protected]>
---
v2: Updated the code to reflect that we know size is always bounded by
GDT_SIZE. This gets rid of the array and the loop. I can throw a few
more comments in there if someone thinks they need to be updated.
---
arch/x86/xen/enlighten_pv.c | 84 ++++++++++++++++-----------------------------
1 file changed, 29 insertions(+), 55 deletions(-)
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index c36d23aa6c35..1254f2fa3a89 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -421,45 +421,32 @@ static void xen_load_gdt(const struct desc_ptr *dtr)
{
unsigned long va = dtr->address;
unsigned int size = dtr->size + 1;
- unsigned pages = DIV_ROUND_UP(size, PAGE_SIZE);
- unsigned long frames[pages];
- int f;
-
- /*
- * A GDT can be up to 64k in size, which corresponds to 8192
- * 8-byte entries, or 16 4k pages..
- */
+ unsigned long pfn, mfn;
+ int level;
+ pte_t *ptep;
+ void *virt;
- BUG_ON(size > 65536);
+ BUG_ON(size > GDT_SIZE);
BUG_ON(va & ~PAGE_MASK);
- for (f = 0; va < dtr->address + size; va += PAGE_SIZE, f++) {
- int level;
- pte_t *ptep;
- unsigned long pfn, mfn;
- void *virt;
-
- /*
- * The GDT is per-cpu and is in the percpu data area.
- * That can be virtually mapped, so we need to do a
- * page-walk to get the underlying MFN for the
- * hypercall. The page can also be in the kernel's
- * linear range, so we need to RO that mapping too.
- */
- ptep = lookup_address(va, &level);
- BUG_ON(ptep == NULL);
-
- pfn = pte_pfn(*ptep);
- mfn = pfn_to_mfn(pfn);
- virt = __va(PFN_PHYS(pfn));
+ /*
+ * The GDT is per-cpu and is in the percpu data area.
+ * That can be virtually mapped, so we need to do a
+ * page-walk to get the underlying MFN for the
+ * hypercall. The page can also be in the kernel's
+ * linear range, so we need to RO that mapping too.
+ */
+ ptep = lookup_address(va, &level);
+ BUG_ON(ptep == NULL);
- frames[f] = mfn;
+ pfn = pte_pfn(*ptep);
+ mfn = pfn_to_mfn(pfn);
+ virt = __va(PFN_PHYS(pfn));
- make_lowmem_page_readonly((void *)va);
- make_lowmem_page_readonly(virt);
- }
+ make_lowmem_page_readonly((void *)va);
+ make_lowmem_page_readonly(virt);
- if (HYPERVISOR_set_gdt(frames, size / sizeof(struct desc_struct)))
+ if (HYPERVISOR_set_gdt(&mfn, size / sizeof(struct desc_struct)))
BUG();
}
@@ -470,34 +457,21 @@ static void __init xen_load_gdt_boot(const struct desc_ptr *dtr)
{
unsigned long va = dtr->address;
unsigned int size = dtr->size + 1;
- unsigned pages = DIV_ROUND_UP(size, PAGE_SIZE);
- unsigned long frames[pages];
- int f;
-
- /*
- * A GDT can be up to 64k in size, which corresponds to 8192
- * 8-byte entries, or 16 4k pages..
- */
+ unsigned long pfn, mfn;
+ pte_t pte;
- BUG_ON(size > 65536);
+ BUG_ON(size > GDT_SIZE);
BUG_ON(va & ~PAGE_MASK);
- for (f = 0; va < dtr->address + size; va += PAGE_SIZE, f++) {
- pte_t pte;
- unsigned long pfn, mfn;
+ pfn = virt_to_pfn(va);
+ mfn = pfn_to_mfn(pfn);
- pfn = virt_to_pfn(va);
- mfn = pfn_to_mfn(pfn);
+ pte = pfn_pte(pfn, PAGE_KERNEL_RO);
- pte = pfn_pte(pfn, PAGE_KERNEL_RO);
-
- if (HYPERVISOR_update_va_mapping((unsigned long)va, pte, 0))
- BUG();
-
- frames[f] = mfn;
- }
+ if (HYPERVISOR_update_va_mapping((unsigned long)va, pte, 0))
+ BUG();
- if (HYPERVISOR_set_gdt(frames, size / sizeof(struct desc_struct)))
+ if (HYPERVISOR_set_gdt(&mfn, size / sizeof(struct desc_struct)))
BUG();
}
--
2.14.3
On 04/18/2018 01:08 PM, Laura Abbott wrote:
> There's an ongoing effort to remove VLAs[1] from the kernel to eventually
> turn on -Wvla. It turns out, the few VLAs in use in Xen produce only a
> single entry array that is always bounded by GDT_SIZE. Clean up the code to
> get rid of the VLA and the loop.
>
> [1] https://lkml.org/lkml/2018/3/7/621
>
> Signed-off-by: Laura Abbott <[email protected]>
> ---
> v2: Updated the code to reflect that we know size is always bounded by
> GDT_SIZE. This gets rid of the array and the loop. I can throw a few
> more comments in there if someone thinks they need to be updated.
> ---
> arch/x86/xen/enlighten_pv.c | 84 ++++++++++++++++-----------------------------
> 1 file changed, 29 insertions(+), 55 deletions(-)
>
> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
> index c36d23aa6c35..1254f2fa3a89 100644
> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -421,45 +421,32 @@ static void xen_load_gdt(const struct desc_ptr *dtr)
> {
> unsigned long va = dtr->address;
> unsigned int size = dtr->size + 1;
> - unsigned pages = DIV_ROUND_UP(size, PAGE_SIZE);
> - unsigned long frames[pages];
> - int f;
> -
> - /*
> - * A GDT can be up to 64k in size, which corresponds to 8192
> - * 8-byte entries, or 16 4k pages..
> - */
> + unsigned long pfn, mfn;
> + int level;
> + pte_t *ptep;
> + void *virt;
>
> - BUG_ON(size > 65536);
> + BUG_ON(size > GDT_SIZE);
I'd probably BUG_ON(size>PAGE_SIZE) because that's what we are really
trying to avoid. Maybe with a comment that we expect GDT_SIZE at most,
and it is less than PAGE_SIZE.
I can fix it while committing if you don't object.
Reviewed-by: Boris Ostrovsky <[email protected]>