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Message-ID: <0b41c28b-20ef-332f-d8d6-e381e05b8252@codeaurora.org>
Date: Mon, 7 Nov 2016 12:00:22 -0500
From: Christopher Covington <cov@...eaurora.org>
To: Dmitry Safonov <dsafonov@...tuozzo.com>,
linux-kernel@...r.kernel.org
Cc: 0x7f454c46@...il.com, Kevin Brodsky <kevin.brodsky@....com>,
Andy Lutomirski <luto@...capital.net>,
Oleg Nesterov <oleg@...hat.com>,
Russell King <linux@...linux.org.uk>,
Will Deacon <will.deacon@....com>,
linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
Cyrill Gorcunov <gorcunov@...nvz.org>,
Pavel Emelyanov <xemul@...tuozzo.com>,
Nathan Lynch <nathan_lynch@...tor.com>,
Will Deacon <Will.Deacon@....com>,
Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH] arm/vdso: introduce vdso_mremap hook
Hi Dmitry,
On 11/01/2016 01:22 PM, Dmitry Safonov wrote:
> Add vdso_mremap hook which will fix context.vdso pointer after mremap()
> on vDSO vma. This is needed for correct landing after syscall execution.
> Primary goal of this is for CRIU on arm - we need to restore vDSO image
> at the exactly same place where the vma was in dumped application. With
> the help of this hook we'll move vDSO at the new position.
> The CRIU code handles situations like when vDSO of dumped application
> was different from vDSO on restoring system. This usally happens when
> some new symbols are being added to vDSO. In these situations CRIU
> inserts jump trampolines from old vDSO blob to new vDSO on restore.
> By that reason even if on restore vDSO blob lies on the same address as
> blob in dumped application - we still need to move it if it differs.
>
> There was previously attempt to add this functionality for arm64 by
> arch_mremap hook [1], while this patch introduces this with minimal
> effort - the same way I've added it to x86:
> commit b059a453b1cf ("x86/vdso: Add mremap hook to vm_special_mapping")
>
> At this moment, vdso restoring code is disabled for arm/arm64 arch
> in CRIU [2], so C/R is only working for !CONFIG_VDSO kernels. This patch
> is aimed to fix that.
> The same hook may be introduced for arm64 kernel, but at this moment
> arm64 vdso code is actively reworked by Kevin, so we can do it on top.
> Separately, I've refactored arch_remap hook out from ppc64 [3].
>
> [1]: https://marc.info/?i=1448455781-26660-1-git-send-email-cov@codeaurora.org
> [2]: https://github.com/xemul/criu/blob/master/Makefile#L39
> [3]: https://marc.info/?i=20161027170948.8279-1-dsafonov@virtuozzo.com
>
> Cc: Kevin Brodsky <kevin.brodsky@....com>
> Cc: Christopher Covington <cov@...eaurora.org>
> Cc: Andy Lutomirski <luto@...capital.net>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Russell King <linux@...linux.org.uk>
> Cc: Will Deacon <will.deacon@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-mm@...ck.org
> Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
> Cc: Pavel Emelyanov <xemul@...tuozzo.com>
> Signed-off-by: Dmitry Safonov <dsafonov@...tuozzo.com>
> ---
> arch/arm/kernel/vdso.c | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> diff --git a/arch/arm/kernel/vdso.c b/arch/arm/kernel/vdso.c
> index 53cf86cf2d1a..d1001f87c2f6 100644
> --- a/arch/arm/kernel/vdso.c
> +++ b/arch/arm/kernel/vdso.c
> @@ -54,8 +54,11 @@ static const struct vm_special_mapping vdso_data_mapping = {
> .pages = &vdso_data_page,
> };
>
> +static int vdso_mremap(const struct vm_special_mapping *sm,
> + struct vm_area_struct *new_vma);
> static struct vm_special_mapping vdso_text_mapping __ro_after_init = {
> .name = "[vdso]",
> + .mremap = vdso_mremap,
> };
>
> struct elfinfo {
> @@ -254,6 +257,24 @@ void arm_install_vdso(struct mm_struct *mm, unsigned long addr)
> mm->context.vdso = addr;
> }
>
> +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_total_pages - 1) << PAGE_SHIFT;
> +
> + /* Disallow partial vDSO blob remap */
> + if (vdso_size != new_size)
> + return -EINVAL;
> +
> + if (WARN_ON_ONCE(current->mm != new_vma->vm_mm))
> + return -EFAULT;
> +
> + current->mm->context.vdso = new_vma->vm_start;
> +
> + return 0;
> +}
> +
> static void vdso_write_begin(struct vdso_data *vdata)
> {
> ++vdso_data->seq_count;
>
What do you think about putting this code somewhere generic (not under
arch/*), so that powerpc and arm64 can reuse it once the cosmetic changes
to make them compatible are made? My thought was that it could be defined
underneath CONFIG_GENERIC_VDSO, which architectures could select as they
became compatible.
Thanks,
Cov
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