Re: [edk2-devel] [PATCH v2 3/5] OvmfPkg/ResetVector: improve page table flag names

["Laszlo Ersek" <lersek@redhat.com>]

On 1/30/24 20:46, Pedro Falcato wrote:
> On Tue, Jan 30, 2024 at 12:32 PM Gerd Hoffmann <kraxel@redhat.com> wrote:
>>
>> Add comments, rename some of the PAGE_* flags and combined attributes.
>> Specifically use "LARGEPAGE" instead of "2M" because that bit is used
>> for both 2M and 1G large pages.
>>
>> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
>> ---
>>  OvmfPkg/ResetVector/Ia32/PageTables64.asm | 39 +++++++++++++----------
>>  1 file changed, 22 insertions(+), 17 deletions(-)
>>
>> diff --git a/OvmfPkg/ResetVector/Ia32/PageTables64.asm b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
>> index 317cad430f29..6fec6f2beeea 100644
>> --- a/OvmfPkg/ResetVector/Ia32/PageTables64.asm
>> +++ b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
>> @@ -10,6 +10,7 @@
>>
>>  BITS    32
>>
>> +; common for all levels
>>  %define PAGE_PRESENT            0x01
>>  %define PAGE_READ_WRITE         0x02
>>  %define PAGE_USER_SUPERVISOR    0x04
>> @@ -17,25 +18,29 @@ BITS    32
>>  %define PAGE_CACHE_DISABLE     0x010
>>  %define PAGE_ACCESSED          0x020
>>  %define PAGE_DIRTY             0x040
>> -%define PAGE_PAT               0x080
>>  %define PAGE_GLOBAL           0x0100
>> -%define PAGE_2M_MBO            0x080
>> -%define PAGE_2M_PAT          0x01000
>> +
>> +; page table entries (level 1)
>> +%define PAGE_PTE_PAT           0x080
>> +
>> +; page directory entries (level 2+)
>> +%define PAGE_PDE_LARGEPAGE     0x080
>> +%define PAGE_PDE_PAT         0x01000
>>
>>  %define PAGE_4K_PDE_ATTR (PAGE_ACCESSED + \
>>                            PAGE_DIRTY + \
>>                            PAGE_READ_WRITE + \
>>                            PAGE_PRESENT)
>>
>> -%define PAGE_2M_PDE_ATTR (PAGE_2M_MBO + \
>> -                          PAGE_ACCESSED + \
>> -                          PAGE_DIRTY + \
>> -                          PAGE_READ_WRITE + \
>> -                          PAGE_PRESENT)
>> +%define PAGE_PDE_LARGEPAGE_ATTR (PAGE_PDE_LARGEPAGE + \
>> +                                 PAGE_ACCESSED + \
>> +                                 PAGE_DIRTY + \
>> +                                 PAGE_READ_WRITE + \
>> +                                 PAGE_PRESENT)
>>
>> -%define PAGE_PDP_ATTR (PAGE_ACCESSED + \
>> -                       PAGE_READ_WRITE + \
>> -                       PAGE_PRESENT)
>> +%define PAGE_PDE_DIRECTORY_ATTR (PAGE_ACCESSED + \
>> +                                 PAGE_READ_WRITE + \
>> +                                 PAGE_PRESENT)
>>
>>  %define TDX_BSP         1
>>  %define TDX_AP          2
>> @@ -84,19 +89,19 @@ clearPageTablesMemoryLoop:
>>      ;
>>      ; Top level Page Directory Pointers (1 * 512GB entry)
>>      ;
>> -    mov     dword[PT_ADDR (0)], PT_ADDR (0x1000) + PAGE_PDP_ATTR
>> +    mov     dword[PT_ADDR (0)], PT_ADDR (0x1000) + PAGE_PDE_DIRECTORY_ATTR
>>      mov     dword[PT_ADDR (4)], edx
>>
>>      ;
>>      ; Next level Page Directory Pointers (4 * 1GB entries => 4GB)
>>      ;
>> -    mov     dword[PT_ADDR (0x1000)], PT_ADDR (0x2000) + PAGE_PDP_ATTR
>> +    mov     dword[PT_ADDR (0x1000)], PT_ADDR (0x2000) + PAGE_PDE_DIRECTORY_ATTR
> 
> Technically, if we want to be pedantic, these are PDPTEs (or PDPs I
> guess), so PDE is misleading here.

I remembered the fact that the SDM used different terms for different
table levels, but honestly, I've never been able to keep all those in my
mind for longer than 5 minutes. I recall them as fairly arbitrary. So I
consciously ignored this; in my book, this doesn't count as misleading.
But, I have nothing against more detailed macro names, if Gerd's willing
to respin!

Laszlo



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