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Re: [Xen-devel] [PATCH] linux/x86-64: allow kernel init memory to be freed

  • To: Jan Beulich <jbeulich@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <keir@xxxxxxxxxxxxx>
  • Date: Fri, 02 Mar 2007 15:23:40 +0000
  • Delivery-date: Fri, 02 Mar 2007 07:22:58 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: Acdc3sFd/75UmsjREduwRgAX8io7RQ==
  • Thread-topic: [Xen-devel] [PATCH] linux/x86-64: allow kernel init memory to be freed

On 2/3/07 11:04, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> +  if (addr >= __START_KERNEL_map) {
> +   /* make_readonly() reports all kernel addresses. */
> +   __make_page_writable(__va(__pa(addr)));
> +   __make_page_readonly((void *)addr);
> +  }

I'm confused by this:
 1. Why does the write-protection need to be changed unconditionally, or
even at all? Is there anything write-protected in the init sections?
 2. Is it safe to keep init mappings above START_KERNEL_map at all, even
read-only? I'd have thought we'd be in trouble if the balloon driver manages
to allocate those pages and tries to free them to Xen. Perhaps they should
be blown away entirely?

 -- Keir

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