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SubjectRe: [PATCH] arm64/vdso: Support mremap() for vDSO
On Wed, Jul 26, 2017 at 08:07:37PM +0300, Dmitry Safonov wrote:
> vDSO VMA address is saved in mm_context for the purpose of using
> restorer from vDSO page to return to userspace after signal handling.
>
> In Checkpoint Restore in Userspace (CRIU) project we place vDSO VMA
> on restore back to the place where it was on the dump.
> With the exception for x86 (where there is API to map vDSO with
> arch_prctl()), we move vDSO inherited from CRIU task to restoree
> position by mremap().
>
> CRIU does support arm64 architecture, but kernel doesn't update
> context.vdso pointer after mremap(). Which results in translation
> fault after signal handling on restored application:
> https://github.com/xemul/criu/issues/288
>
> Make vDSO code track the VMA address by supplying .mremap() fops
> the same way it's done for x86 and arm32 by:
> commit b059a453b1cf ("x86/vdso: Add mremap hook to vm_special_mapping")
> commit 280e87e98c09 ("ARM: 8683/1: ARM32: Support mremap() for sigpage/vDSO").
>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Russell King <rmk+kernel@armlinux.org.uk>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: Cyrill Gorcunov <gorcunov@openvz.org>
> Cc: Pavel Emelyanov <xemul@virtuozzo.com>
> Cc: Christopher Covington <cov@codeaurora.org>
> Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
> ---
> arch/arm64/kernel/vdso.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
> index e8f759f764f2..2d419006ad43 100644
> --- a/arch/arm64/kernel/vdso.c
> +++ b/arch/arm64/kernel/vdso.c
> @@ -110,12 +110,27 @@ int aarch32_setup_vectors_page(struct linux_binprm *bprm, int uses_interp)
> }
> #endif /* CONFIG_COMPAT */
>
> +static int vdso_mremap(const struct vm_special_mapping *sm,
> + struct vm_area_struct *new_vma)
> +{
> + unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
> + unsigned long vdso_size = vdso_end - vdso_start;

You might be able to use vdso_pages here, but it depends on my question
below.

> +
> + if (vdso_size != new_size)
> + return -EINVAL;
> +
> + current->mm->context.vdso = (void *)new_vma->vm_start;
> +
> + return 0;
> +}
> +
> static struct vm_special_mapping vdso_spec[2] __ro_after_init = {
> {
> .name = "[vvar]",
> },
> {
> .name = "[vdso]",
> + .mremap = vdso_mremap,

Does this mean we move the vdso text, but not the data page? How does that
work?

Will

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