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

[Juergen Gross <jgross@xxxxxxxx>]

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.

> So, maybe it should be called grub_xen_alloc_boot_data() or something like 
> that.
> 
>>>> +  return GRUB_ERR_NONE;
>>>> +}
>>>> +
>>>> +static grub_err_t
>>>>  grub_xen_boot (void)
>>>>  {
>>>>    grub_err_t err;
>>>> @@ -330,13 +357,7 @@ grub_xen_boot (void)
>>>>    if (grub_xen_n_allocated_shared_pages)
>>>>      return grub_error (GRUB_ERR_BUG, "active grants");
>>>>
>>>> -  err = grub_xen_p2m_alloc ();
>>>> -  if (err)
>>>> -    return err;
>>>> -  err = grub_xen_special_alloc ();
>>>> -  if (err)
>>>> -    return err;
>>>> -  err = grub_xen_pt_alloc ();
>>>> +  err = grub_xen_alloc_final ();
>>>
>>> if (!xen_state.xen_inf.unmapped_initrd)
>>>   {
>>>     err = grub_xen_alloc_final ();
>>>     if (err)
>>>       goto fail;
>>>   }
>>>
>>> This way you avoid checks in grub_xen_p2m_alloc(),
>>> grub_xen_special_alloc() and grub_xen_pt_alloc().
>>
>> No. In case there is no initrd, but the kernel does support an unmapped
>> initrd, I would omit allocating special pages, p2m and page tables.
> 
> Ups... I have missed that.
> 
>>>>    if (err)
>>>>      return err;
>>>>
>>>> @@ -610,6 +631,13 @@ grub_cmd_initrd (grub_command_t cmd __attribute__ 
>>>> ((unused)),
>>>>        goto fail;
>>>>      }
>>>>
>>>> +  if (xen_state.xen_inf.unmapped_initrd)
>>>> +    {
>>>> +      err = grub_xen_alloc_final ();
>>>> +      if (err)
>>>> +  goto fail;
>>>> +    }
>>>> +
>>>>    if (grub_initrd_init (argc, argv, &initrd_ctx))
>>>>      goto fail;
>>>>
>>>> @@ -627,14 +655,24 @@ grub_cmd_initrd (grub_command_t cmd __attribute__ 
>>>> ((unused)),
>>>>    goto fail;
>>>>      }
>>>>
>>>> -  xen_state.next_start.mod_start =
>>>> -    xen_state.max_addr + xen_state.xen_inf.virt_base;
>>>> -  xen_state.next_start.mod_len = size;
>>>
>>> Leave "xen_state.next_start.mod_len = size;" as is here and...
>>>
>>>> -
>>>> -  xen_state.max_addr = ALIGN_UP (xen_state.max_addr + size, PAGE_SIZE);
>>>> +  if (xen_state.xen_inf.unmapped_initrd)
>>>> +    {
>>>> +      xen_state.next_start.flags |= SIF_MOD_START_PFN;
>>>> +      xen_state.next_start.mod_start = xen_state.max_addr >> PAGE_SHIFT;
>>>> +      xen_state.next_start.mod_len = size;
>>>
>>> ... do not add it here...
>>>
>>>> +    }
>>>> +  else
>>>> +    {
>>>> +      xen_state.next_start.mod_start =
>>>> +  xen_state.max_addr + xen_state.xen_inf.virt_base;
>>>> +      xen_state.next_start.mod_len = size;
>>>
>>> ... and here...
>>>
>>>> +    }
>>>
>>> ... and you do not need curly brackets then.
>>
>> I still do, as in the "if" part I still have two statements.
> 
> Yep, but else stuff does not need one.

Ah, okay. Too many different coding styles. Linux kernel would keep
the braces.

> 
>>>>    grub_dprintf ("xen", "Initrd, addr=0x%x, size=0x%x\n",
>>>> -          (unsigned) xen_state.next_start.mod_start, (unsigned) size);
>>>> +          (unsigned) (xen_state.max_addr + xen_state.xen_inf.virt_base),
>>>> +          (unsigned) size);
>>>
>>> This should be printed only if !xen_state.xen_inf.unmapped_initrd.
>>
>> Really? Why? We still have an initrd.
>>
>>> Why do not use xen_state.next_start.mod_start here?
>>
>> It is the pfn in case of unmapped_initrd.
> 
> Errr... I have looked at wrong line. Sorry about that.

NP.


Juergen


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