Re: [PATCH v2 3/8] xen/x86: Construct the {l2, l3}_bootmap at compile time

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 24/02/16 11:50, Jan Beulich wrote:
>>>> On 24.02.16 at 12:40, <andrew.cooper3@citrix.com> wrote:
>> On 24/02/16 11:34, Jan Beulich wrote:
>>>>>> On 23.02.16 at 17:31, <andrew.cooper3@citrix.com> wrote:
>>>> ---
>>>>  xen/arch/x86/boot/head.S   | 18 +++++-------------
>>>>  xen/arch/x86/boot/x86_64.S | 19 +++++++++++++++++++
>>>>  xen/arch/x86/x86_64/mm.c   |  4 ----
>>>>  3 files changed, 24 insertions(+), 17 deletions(-)
>>> Is this intentionally leaving the EFI equivalent untouched?
>> Yes.
>>
>>>> --- a/xen/arch/x86/boot/x86_64.S
>>>> +++ b/xen/arch/x86/boot/x86_64.S
>>>> @@ -184,3 +184,22 @@ GLOBAL(idle_pg_table)
>>>>          .size idle_pg_table, . - idle_pg_table
>>>>  
>>>>  GLOBAL(__page_tables_end)
>>>> +
>>>> +/* Init pagetables.  Enough page directories to map into the bottom 1GB. */
>>>> +        .section .init.data, "a", @progbits
>>>> +        .align PAGE_SIZE, 0
>>>> +
>>>> +GLOBAL(l2_bootmap)
>>>> +        .quad sym_phys(l1_identmap) + __PAGE_HYPERVISOR
>>> The relocation needed for this and ...
>>>
>>>> +        idx = 1
>>>> +        .rept 7
>>>> +        .quad (idx << L2_PAGETABLE_SHIFT) | __PAGE_HYPERVISOR | _PAGE_PSE
>>>> +        idx = idx + 1
>>>> +        .endr
>>>> +        .fill L2_PAGETABLE_ENTRIES - 8, 8, 0
>>>> +        .size l2_bootmap, . - l2_bootmap
>>>> +
>>>> +GLOBAL(l3_bootmap)
>>>> +        .quad sym_phys(l2_bootmap) + __PAGE_HYPERVISOR
>>> ... this won't get properly adjusted by efi_arch_relocate_image(),
>>> due to living outside of [__page_tables_start, __page_tables_end).
>> Deliberately so.
>>
>> The EFI needs to relocate the tables anyway.  It currently (re)writes
>> them fresh at the relocated address, and leaving this be is the more
>> simple option.
> Okay, I guess you mean to say that both together continue to
> work, which without it being said explicitly (allowing the implication
> that this also has got tested) I was rather unsure about. Hence
> I'd like to at least ask for an explicit respective statement in the
> commit message.

Ok.  The other reason why leaving the EFI side along is that these
tables can't both be in .init.data and covered by [__page_tables_start,
__page_tables_end).

~Andrew