Re: [PATCH v2 1/6] xen: factor out p2m list allocation into separate function

[Juergen Gross <jgross@suse.com>]

On 11/02/16 18:09, Daniel Kiper wrote:
> On Thu, Feb 11, 2016 at 01:38:10PM +0100, Juergen Gross wrote:
>> On 11/02/16 13:19, Daniel Kiper wrote:
>>> On Thu, Feb 11, 2016 at 08:53:21AM +0100, Juergen Gross wrote:
>>>> Do the p2m list allocation of the to be loaded kernel in a separate
>>>> function. This will allow doing the p2m list allocation at different
>>>> times of the boot preparations depending on the features the kernel
>>>> is supporting.
>>>>
>>>> While at this remove superfluous setting of first_p2m_pfn and
>>>> nr_p2m_frames as those are needed only in case of the p2m list not
>>>> being mapped by the initial kernel mapping.
>>>>
>>>> Signed-off-by: Juergen Gross <jgross@suse.com>
>>>> ---
>>>>  grub-core/loader/i386/xen.c | 70 ++++++++++++++++++++++++++-------------------
>>>>  1 file changed, 40 insertions(+), 30 deletions(-)
>>>>
>>>> diff --git a/grub-core/loader/i386/xen.c b/grub-core/loader/i386/xen.c
>>>> index c4d9689..42ed7c7 100644
>>>> --- a/grub-core/loader/i386/xen.c
>>>> +++ b/grub-core/loader/i386/xen.c
>>>> @@ -52,6 +52,8 @@ static struct grub_xen_file_info xen_inf;
>>>>  static struct xen_multiboot_mod_list *xen_module_info_page;
>>>>  static grub_uint64_t modules_target_start;
>>>>  static grub_size_t n_modules;
>>>> +static struct grub_relocator_xen_state state;
>>>> +static grub_xen_mfn_t *virt_mfn_list;
>>>
>>> Do we strongly need this as globals? I suppose that
>>> both of them could be local to grub_xen_boot.
>>
>> This would require passing the state pointer to many other functions.
>> Same applies to virt_mfn_list.
>>
>> I just followed the style used in the source already: variables used in
>> multiple functions are mostly defined globally (there are even some
>> which are used in one function only).
> 
> Well, I do not like that style but if maintainer do not object I will
> do not complain more here about that.
> 
>>>>  #define PAGE_SIZE 4096
>>>>  #define MAX_MODULES (PAGE_SIZE / sizeof (struct xen_multiboot_mod_list))
>>>> @@ -166,7 +168,7 @@ generate_page_table (grub_uint64_t *where, grub_uint64_t paging_start,
>>>>  }
>>>>
>>>>  static grub_err_t
>>>> -set_mfns (grub_xen_mfn_t * new_mfn_list, grub_xen_mfn_t pfn)
>>>> +set_mfns (grub_xen_mfn_t pfn)
>>>>  {
>>>>    grub_xen_mfn_t i, t;
>>>>    grub_xen_mfn_t cn_pfn = -1, st_pfn = -1;
>>>> @@ -175,32 +177,32 @@ set_mfns (grub_xen_mfn_t * new_mfn_list, grub_xen_mfn_t pfn)
>>>>
>>>>    for (i = 0; i < grub_xen_start_page_addr->nr_pages; i++)
>>>>      {
>>>> -      if (new_mfn_list[i] == grub_xen_start_page_addr->console.domU.mfn)
>>>> +      if (virt_mfn_list[i] == grub_xen_start_page_addr->console.domU.mfn)
>>>>  	cn_pfn = i;
>>>> -      if (new_mfn_list[i] == grub_xen_start_page_addr->store_mfn)
>>>> +      if (virt_mfn_list[i] == grub_xen_start_page_addr->store_mfn)
>>>>  	st_pfn = i;
>>>>      }
>>>>    if (cn_pfn == (grub_xen_mfn_t)-1)
>>>>      return grub_error (GRUB_ERR_BUG, "no console");
>>>>    if (st_pfn == (grub_xen_mfn_t)-1)
>>>>      return grub_error (GRUB_ERR_BUG, "no store");
>>>> -  t = new_mfn_list[pfn];
>>>> -  new_mfn_list[pfn] = new_mfn_list[cn_pfn];
>>>> -  new_mfn_list[cn_pfn] = t;
>>>> -  t = new_mfn_list[pfn + 1];
>>>> -  new_mfn_list[pfn + 1] = new_mfn_list[st_pfn];
>>>> -  new_mfn_list[st_pfn] = t;
>>>> -
>>>> -  m2p_updates[0].ptr = page2offset (new_mfn_list[pfn]) | MMU_MACHPHYS_UPDATE;
>>>> +  t = virt_mfn_list[pfn];
>>>> +  virt_mfn_list[pfn] = virt_mfn_list[cn_pfn];
>>>> +  virt_mfn_list[cn_pfn] = t;
>>>> +  t = virt_mfn_list[pfn + 1];
>>>> +  virt_mfn_list[pfn + 1] = virt_mfn_list[st_pfn];
>>>> +  virt_mfn_list[st_pfn] = t;
>>>> +
>>>> +  m2p_updates[0].ptr = page2offset (virt_mfn_list[pfn]) | MMU_MACHPHYS_UPDATE;
>>>>    m2p_updates[0].val = pfn;
>>>>    m2p_updates[1].ptr =
>>>> -    page2offset (new_mfn_list[pfn + 1]) | MMU_MACHPHYS_UPDATE;
>>>> +    page2offset (virt_mfn_list[pfn + 1]) | MMU_MACHPHYS_UPDATE;
>>>>    m2p_updates[1].val = pfn + 1;
>>>>    m2p_updates[2].ptr =
>>>> -    page2offset (new_mfn_list[cn_pfn]) | MMU_MACHPHYS_UPDATE;
>>>> +    page2offset (virt_mfn_list[cn_pfn]) | MMU_MACHPHYS_UPDATE;
>>>>    m2p_updates[2].val = cn_pfn;
>>>>    m2p_updates[3].ptr =
>>>> -    page2offset (new_mfn_list[st_pfn]) | MMU_MACHPHYS_UPDATE;
>>>> +    page2offset (virt_mfn_list[st_pfn]) | MMU_MACHPHYS_UPDATE;
>>>>    m2p_updates[3].val = st_pfn;
>>>>
>>>>    grub_xen_mmu_update (m2p_updates, 4, NULL, DOMID_SELF);
>>>> @@ -209,34 +211,43 @@ set_mfns (grub_xen_mfn_t * new_mfn_list, grub_xen_mfn_t pfn)
>>>>  }
>>>>
>>>>  static grub_err_t
>>>> +grub_xen_p2m_alloc (void)
>>>> +{
>>>> +  grub_relocator_chunk_t ch;
>>>> +  grub_size_t p2msize;
>>>> +  grub_err_t err;
>>>> +
>>>> +  state.mfn_list = max_addr;
>>>> +  next_start.mfn_list = max_addr + xen_inf.virt_base;
>>>> +  p2msize = sizeof (grub_xen_mfn_t) * grub_xen_start_page_addr->nr_pages;
>>>> +  err = grub_relocator_alloc_chunk_addr (relocator, &ch, max_addr, p2msize);
>>>
>>> Hmmm.... Where relocator is defined?
>>
>> First global variable in this source.
>>
>>>
>>>> +  if (err)
>>>> +    return err;
>>>> +  virt_mfn_list = get_virtual_current_address (ch);
>>>> +  grub_memcpy (virt_mfn_list,
>>>> +	       (void *) grub_xen_start_page_addr->mfn_list, p2msize);
>>>> +  max_addr = ALIGN_UP (max_addr + p2msize, PAGE_SIZE);
>>>> +
>>>> +  return GRUB_ERR_NONE;
>>>> +}
>>>> +
>>>> +static grub_err_t
>>>>  grub_xen_boot (void)
>>>>  {
>>>> -  struct grub_relocator_xen_state state;
>>>>    grub_relocator_chunk_t ch;
>>>>    grub_err_t err;
>>>> -  grub_size_t pgtsize;
>>>>    struct start_info *nst;
>>>>    grub_uint64_t nr_info_pages;
>>>>    grub_uint64_t nr_pages, nr_pt_pages, nr_need_pages;
>>>>    struct gnttab_set_version gnttab_setver;
>>>> -  grub_xen_mfn_t *new_mfn_list;
>>>>    grub_size_t i;
>>>>
>>>>    if (grub_xen_n_allocated_shared_pages)
>>>>      return grub_error (GRUB_ERR_BUG, "active grants");
>>>>
>>>> -  state.mfn_list = max_addr;
>>>> -  next_start.mfn_list = max_addr + xen_inf.virt_base;
>>>> -  next_start.first_p2m_pfn = max_addr >> PAGE_SHIFT;	/* Is this right? */
>>>> -  pgtsize = sizeof (grub_xen_mfn_t) * grub_xen_start_page_addr->nr_pages;
>>>> -  err = grub_relocator_alloc_chunk_addr (relocator, &ch, max_addr, pgtsize);
>>>> -  next_start.nr_p2m_frames = (pgtsize + PAGE_SIZE - 1) >> PAGE_SHIFT;
>>>> +  err = grub_xen_p2m_alloc ();
>>>>    if (err)
>>>>      return err;
>>>> -  new_mfn_list = get_virtual_current_address (ch);
>>>> -  grub_memcpy (new_mfn_list,
>>>> -	       (void *) grub_xen_start_page_addr->mfn_list, pgtsize);
>>>> -  max_addr = ALIGN_UP (max_addr + pgtsize, PAGE_SIZE);
>>>>
>>>>    err = grub_relocator_alloc_chunk_addr (relocator, &ch,
>>>
>>> Ditto. I think that this could be passed as a grub_xen_boot() argument.
>>> Otherwise this appear from nowhere and reading/understanding is more
>>> difficult.
>>
>> Huh? How that? grub_xen_boot() can't have any parameters (see prototype
>> of grub_loader_set() which is used with grub_xen_boot() as parameter).
>>
>> BTW: I didn't introduce this kind of usage of relocator.
> 
> OK, I have checked other loaders and it looks that they use relocator in
> the same way. Let's leave it as is. However, this does not waive my
> concerns expressed above in regards to other global variables.

See my reply to patch 4. I'll change my series.


Juergen