On Tue, Jun 16, 2020 at 12:55:40AM -0700, Andrei Vagin wrote:
> This is required to support time namespaces where a time namespace data
> page is different for each namespace.
Can you please give a bit more of an introduction to the changes here?
As-is, this doesn't give reviewers the necessary context to understand
the change, nor does it justify it.
Ideally, a commit message for this should look something like:
| Currently the vdso has no awareness of time namespaces, which may
| apply distinct offsets to processes in different namespaces. To handle
| this within the vdso, we'll need to expose a per-namespace data page.
|
| As a preparatory step, this patch separates the vdso data page from
| the code pages, and has it faulted in via its own fault callback.
| Subsquent patches will extend this to support distinct pages per time
| namespace.
Otherwise, I have a few minor comments below.
> Reviewed-by: Vincenzo Frascino <vincenzo.frasc...@arm.com>
> Reviewed-by: Dmitry Safonov <d...@arista.com>
> Signed-off-by: Andrei Vagin <ava...@gmail.com>
> ---
> arch/arm64/kernel/vdso.c | 24 +++++++++++++++---------
> 1 file changed, 15 insertions(+), 9 deletions(-)
>
> diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
> index 4e016574bd91..b0aec4e8c9b4 100644
> --- a/arch/arm64/kernel/vdso.c
> +++ b/arch/arm64/kernel/vdso.c
> @@ -108,28 +108,32 @@ static int __vdso_init(enum vdso_abi abi)
> PAGE_SHIFT;
>
> /* Allocate the vDSO pagelist, plus a page for the data. */
> - vdso_pagelist = kcalloc(vdso_info[abi].vdso_pages + 1,
> + vdso_pagelist = kcalloc(vdso_info[abi].vdso_pages,
> sizeof(struct page *),
> GFP_KERNEL);
The comment above is now stale. Can you please update it, or (event
better) delete it entirely?
> if (vdso_pagelist == NULL)
> return -ENOMEM;
>
> - /* Grab the vDSO data page. */
> - vdso_pagelist[0] = phys_to_page(__pa_symbol(vdso_data));
> -
> -
> /* Grab the vDSO code pages. */
> pfn = sym_to_pfn(vdso_info[abi].vdso_code_start);
>
> for (i = 0; i < vdso_info[abi].vdso_pages; i++)
> - vdso_pagelist[i + 1] = pfn_to_page(pfn + i);
> + vdso_pagelist[i] = pfn_to_page(pfn + i);
>
> - vdso_info[abi].dm->pages = &vdso_pagelist[0];
> - vdso_info[abi].cm->pages = &vdso_pagelist[1];
> + vdso_info[abi].cm->pages = vdso_pagelist;
>
> return 0;
> }
>
> +static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
> + struct vm_area_struct *vma, struct vm_fault *vmf)
> +{
> + if (vmf->pgoff == 0)
> + return vmf_insert_pfn(vma, vmf->address,
> + sym_to_pfn(vdso_data));
> + return VM_FAULT_SIGBUS;
> +}
This might look better as:
| if (vmf->pgoff != 0)
| return VM_FAULT_SIGBUS;
|
| return vmf_insert_pfn(vma, vmf->address, sym_to_pfn(vdso_data));
> +
> static int __setup_additional_pages(enum vdso_abi abi,
> struct mm_struct *mm,
> struct linux_binprm *bprm,
> @@ -150,7 +154,7 @@ static int __setup_additional_pages(enum vdso_abi abi,
> }
>
> ret = _install_special_mapping(mm, vdso_base, PAGE_SIZE,
> - VM_READ|VM_MAYREAD,
> + VM_READ|VM_MAYREAD|VM_PFNMAP,
This change needs to be explained in the commit message. WHy is it
necessary, and why only so for the data page?
Thanks,
Mark.
> vdso_info[abi].dm);
> if (IS_ERR(ret))
> goto up_fail;
> @@ -209,6 +213,7 @@ static struct vm_special_mapping aarch32_vdso_maps[] = {
> #ifdef CONFIG_COMPAT_VDSO
> [AA32_MAP_VVAR] = {
> .name = "[vvar]",
> + .fault = vvar_fault,
> },
> [AA32_MAP_VDSO] = {
> .name = "[vdso]",
> @@ -376,6 +381,7 @@ enum aarch64_map {
> static struct vm_special_mapping aarch64_vdso_maps[] __ro_after_init = {
> [AA64_MAP_VVAR] = {
> .name = "[vvar]",
> + .fault = vvar_fault,
> },
> [AA64_MAP_VDSO] = {
> .name = "[vdso]",
> --
> 2.24.1
>
