Re: [Xen-devel] [PATCH v5 09/11] xen: add capability to load initrd outside of initial mapping

[Juergen Gross <jgross@xxxxxxxx>]

On 29/02/16 16:43, Daniel Kiper wrote:
> On Mon, Feb 29, 2016 at 09:27:42AM +0100, Juergen Gross wrote:
>> On 26/02/16 16:41, Daniel Kiper wrote:
>>> On Fri, Feb 26, 2016 at 03:28:21PM +0100, Juergen Gross wrote:
>>>> On 26/02/16 15:00, Daniel Kiper wrote:
>>>>> On Thu, Feb 25, 2016 at 04:33:46PM +0100, Juergen Gross wrote:
>>>>>> On 25/02/16 13:47, Daniel Kiper wrote:
>>>>>>> On Thu, Feb 25, 2016 at 12:33:35PM +0100, Juergen Gross wrote:
>>>>>>>> Modern pvops linux kernels support an initrd not covered by the initial
>>>>>>>> mapping. This capability is flagged by an elf-note.
>>>>>>>>
>>>>>>>> In case the elf-note is set by the kernel don't place the initrd into
>>>>>>>> the initial mapping. This will allow to load larger initrds and/or
>>>>>>>> support domains with larger memory, as the initial mapping is limited
>>>>>>>> to 2GB and it is containing the p2m list.
>>>>>>>>
>>>>>>>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>>>>>>>> ---
>>>>>>>> V5: let call grub_xen_alloc_final() all subfunctions unconditionally
>>>>>>>>     and let them decide whether they need to do anything
>>>>>>>> V4: rename grub_xen_alloc_end() to grub_xen_alloc_final()
>>>>>>>> ---
>>>>>>>>  grub-core/loader/i386/xen.c        | 65 
>>>>>>>> ++++++++++++++++++++++++++++++--------
>>>>>>>>  grub-core/loader/i386/xen_fileXX.c |  3 ++
>>>>>>>>  include/grub/xen_file.h            |  1 +
>>>>>>>>  3 files changed, 56 insertions(+), 13 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/grub-core/loader/i386/xen.c b/grub-core/loader/i386/xen.c
>>>>>>>> index 2e12763..466f0c0 100644
>>>>>>>> --- a/grub-core/loader/i386/xen.c
>>>>>>>> +++ b/grub-core/loader/i386/xen.c
>>>>>>>> @@ -228,6 +228,9 @@ grub_xen_p2m_alloc (void)
>>>>>>>>    grub_size_t p2msize;
>>>>>>>>    grub_err_t err;
>>>>>>>>
>>>>>>>> +  if (xen_state.virt_mfn_list)
>>>>>>>> +    return GRUB_ERR_NONE;
>>>>>>>> +
>>>>>>>>    xen_state.state.mfn_list = xen_state.max_addr;
>>>>>>>>    xen_state.next_start.mfn_list =
>>>>>>>>      xen_state.max_addr + xen_state.xen_inf.virt_base;
>>>>>>>> @@ -250,6 +253,9 @@ grub_xen_special_alloc (void)
>>>>>>>>    grub_relocator_chunk_t ch;
>>>>>>>>    grub_err_t err;
>>>>>>>>
>>>>>>>> +  if (xen_state.virt_start_info)
>>>>>>>> +    return GRUB_ERR_NONE;
>>>>>>>> +
>>>>>>>>    err = grub_relocator_alloc_chunk_addr (xen_state.relocator, &ch,
>>>>>>>>                                         xen_state.max_addr,
>>>>>>>>                                         sizeof (xen_state.next_start));
>>>>>>>> @@ -281,6 +287,9 @@ grub_xen_pt_alloc (void)
>>>>>>>>    grub_uint64_t nr_info_pages;
>>>>>>>>    grub_uint64_t nr_pages, nr_pt_pages, nr_need_pages;
>>>>>>>>
>>>>>>>> +  if (xen_state.virt_pgtable)
>>>>>>>> +    return GRUB_ERR_NONE;
>>>>>>>> +
>>>>>>>>    xen_state.next_start.pt_base =
>>>>>>>>      xen_state.max_addr + xen_state.xen_inf.virt_base;
>>>>>>>>    xen_state.state.paging_start = xen_state.max_addr >> PAGE_SHIFT;
>>>>>>>> @@ -320,6 +329,24 @@ grub_xen_pt_alloc (void)
>>>>>>>>  }
>>>>>>>>
>>>>>>>>  static grub_err_t
>>>>>>>> +grub_xen_alloc_final (void)
>>>>>>>> +{
>>>>>>>> +  grub_err_t err;
>>>>>>>> +
>>>>>>>> +  err = grub_xen_p2m_alloc ();
>>>>>>>> +  if (err)
>>>>>>>> +    return err;
>>>>>>>> +  err = grub_xen_special_alloc ();
>>>>>>>> +  if (err)
>>>>>>>> +    return err;
>>>>>>>> +  err = grub_xen_pt_alloc ();
>>>>>>>> +  if (err)
>>>>>>>> +    return err;
>>>>>>>
>>>>>>> Could you move grub_xen_p2m_alloc() here? This way 
>>>>>>> grub_xen_alloc_final()
>>>>>>> will be real final in patch 11 and you do not need an extra condition
>>>>>>> around grub_xen_p2m_alloc().
>>>>>>
>>>>>> No. Page tables must be allocated after p2m unless p2m is outside of
>>>>>> initial kernel mapping (patch 11).
>>>>>
>>>>> OK, I was afraid of that. However, then grub_xen_alloc_final() is not 
>>>>> final.
>>>>
>>>> Sure it is. Patch 11 just adds allocation to grub_xen_alloc_final(), not
>>>> after it.
>>>
>>> Excerpt from patch 11:
>>>
>>> @@ -474,6 +503,12 @@ grub_xen_boot (void)
>>>    err = grub_xen_alloc_final ();
>>>    if (err)
>>>      return err;
>>> +  if (xen_state.xen_inf.has_p2m_base)
>>> +    {
>>> +      err = grub_xen_p2m_alloc ();
>>> +      if (err)
>>> +        return err;
>>> +    }
>>>
>>
>> Hmph. No idea what I looked at when writing my previous reply.
>>
>>>>> So, maybe it should be called grub_xen_alloc_boot_data() or something 
>>>>> like that.
>>>
>>> Then my previous comment is still valid.
>>
>> What about naming it grub_xen_alloc_kernel_mapping() ? This is what it
>> really does: It is allocating all not yet allocated areas which are to
>> be included in the initial kernel mapping.
> 
> This function does three things:
>   - allocate memory for p2m array,
>   - allocate special pages (e.g. console),
>   - allocate memory for page tables.
> 
> Three of them are part of boot data described by struct start_info.
> Well, there are also other required stuff to properly boot PV guest.
> So, I can agree that grub_xen_alloc_boot_data() is not perfect but
> I cannot find anything better. Additionally, IMO 
> grub_xen_alloc_kernel_mapping()
> is not right choice too. It suggests that this functions does anything
> with kernel mapping. Yep, it does, however, this is only one third
> of this function. So, I tend to use my proposal or anything better
> which is short and quite well describes what is going in this
> function as whole.

Yeah. grub_xen_alloc_stuff() with a nice comment. ;-)

Okay, lets stick with grub_xen_alloc_boot_data() and add a comment
explaining that the function will allocate everything not yet allocated
and covered by the initial page tables.


Juergen


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