Messages in this thread | | | Date | Tue, 16 Jun 2020 11:59:20 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH 1/6] arm64/vdso: use the fault callback to map vvar pages |
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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.frascino@arm.com> > Reviewed-by: Dmitry Safonov <dima@arista.com> > Signed-off-by: Andrei Vagin <avagin@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 >
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