Re: [RFC PATCH v2 07/20] x86: Provide general kernel support for memory encryption

[Tom Lendacky]

On 09/05/2016 03:48 AM, Borislav Petkov wrote:
> On Mon, Aug 22, 2016 at 05:36:46PM -0500, Tom Lendacky wrote:
>> Adding general kernel support for memory encryption includes:
>> - Modify and create some page table macros to include the Secure Memory
>>   Encryption (SME) memory encryption mask
>> - Update kernel boot support to call an SME routine that checks for and
>>   sets the SME capability (the SME routine will grow later and for now
>>   is just a stub routine)
>> - Update kernel boot support to call an SME routine that encrypts the
>>   kernel (the SME routine will grow later and for now is just a stub
>>   routine)
>> - Provide an SME initialization routine to update the protection map with
>>   the memory encryption mask so that it is used by default
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
>> ---
> 
> ...
> 
>> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
>> index f1218f5..a01f0e1 100644
>> --- a/arch/x86/include/asm/pgtable_types.h
>> +++ b/arch/x86/include/asm/pgtable_types.h
>> @@ -3,6 +3,7 @@
>>  
>>  #include <linux/const.h>
>>  #include <asm/page_types.h>
>> +#include <asm/mem_encrypt.h>
>>  
>>  #define FIRST_USER_ADDRESS	0UL
>>  
>> @@ -121,9 +122,9 @@
>>  
>>  #define _PAGE_PROTNONE	(_AT(pteval_t, 1) << _PAGE_BIT_PROTNONE)
>>  
>> -#define _PAGE_TABLE	(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER |	\
>> +#define __PAGE_TABLE	(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER |	\
>>  			 _PAGE_ACCESSED | _PAGE_DIRTY)
> 
> Hmm, so this naming looks confusing and error-prone: the only difference
> is a single "_".
> 
> How about this instead:
> 
> #define _PAGE_TABLE_NO_ENC	(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER |	\
> 	  			 _PAGE_ACCESSED | _PAGE_DIRTY)
> 
> #define _PAGE_TABLE (_PAGE_TABLE_NO_ENC | _PAGE_ENC)
> 
> Or call it _PAGE_TABLE_BASE or whatever.
> 
> Ditto for __KERNPG_TABLE.
> 
> This way you can differentiate between the two and use the _NO_ENC one
> to define _PAGE_TABLE. And it will be absolutely clear when you use the
> _NO_ENC one, what you mean and that you don't want to have the enc mask
> in the PTE.
> 
> Should be less confusing IMO too.

Yup, makes sense.  I'll rework/rename.

Thanks,
Tom

>