Re: [PATCH v3 4/4] kexec, x86_64: Load bzImage64 above 4G

["H. Peter Anvin" <hpa@zytor.com>]

On 11/21/2012 11:54 AM, Yinghai Lu wrote:
> On Wed, Nov 21, 2012 at 6:37 AM, Vivek Goyal <vgoyal@redhat.com> wrote:
>> On Tue, Nov 20, 2012 at 11:31:38PM -0800, Yinghai Lu wrote:
>>
>> [..]
>>> +     /* avoid cross GB boundary */
>>> +     align = real_mode->kernel_alignment;
>>> +     addr = locate_hole(info, size, align, 0x100000, -1, -1);
>>> +     if (addr == ULONG_MAX)
>>> +             die("can not load bzImage64");
>>> +     /* same GB ? */
>>> +     while ((addr >> 30) != ((addr + size - 1) >> 30)) {
>>> +             addr = locate_hole(info, size, align, 0x100000,
>>> +                              round_down(addr + size - 1, (1UL<<30)), -1);
>>> +             if (addr == ULONG_MAX)
>>> +                     die("can not load bzImage64");
>>> +     }
>>> +     dbgprintf("Found kernel buffer at %lx size %lx\n", addr, size);
>>
>> Where does this limitation of not loading kernel across GB boundary come
>> from?
> 
> in kernel arch/x86/kernel/head_64.S
> 
> it only set first 1G ident mapping. and if it find that code is above
> 1G, it will set extra ident mapping
> for new _text.._end.
> To make checking and add extra mapping simple and also save two extra
> pages for mapping.
> Limit that _text.._end in them same GB range.
> 

No, this is backwards.

We should fix that limitation instead.

	-hpa



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