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

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Date:   Wed, 7 Sep 2016 09:11:35 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     <linux-arch@...r.kernel.org>, <linux-efi@...r.kernel.org>,
        <kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        <kasan-dev@...glegroups.com>, <linux-mm@...ck.org>,
        <iommu@...ts.linux-foundation.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v2 07/20] x86: Provide general kernel support for
 memory encryption

On 09/02/2016 01:14 PM, 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@....com>
>> ---
> 
> ...
> 
>> diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
>> index 747fc52..9f3e762 100644
>> --- a/arch/x86/include/asm/mem_encrypt.h
>> +++ b/arch/x86/include/asm/mem_encrypt.h
>> @@ -15,12 +15,21 @@
>>  
>>  #ifndef __ASSEMBLY__
>>  
>> +#include <linux/init.h>
>> +
>>  #ifdef CONFIG_AMD_MEM_ENCRYPT
>>  
>>  extern unsigned long sme_me_mask;
>>  
>>  u8 sme_get_me_loss(void);
>>  
>> +void __init sme_early_init(void);
>> +
>> +#define __sme_pa(x)		(__pa((x)) | sme_me_mask)
>> +#define __sme_pa_nodebug(x)	(__pa_nodebug((x)) | sme_me_mask)
>> +
>> +#define __sme_va(x)		(__va((x) & ~sme_me_mask))
> 
> So I'm wondering: why not push the masking off of the SME mask into the
> __va() macro instead of defining a specific __sme_va() one?
> 
> I mean, do you even see cases where __va() would need to have to
> sme_mask left in the virtual address?
> 
> Because if not, you could mask it out in __va() so that all __va() users
> get the "clean" va, without the enc bits.

That's a good point, yes, it could go in __va().  I'll make that change.

> 
> Hmmm.
> 
> Btw, this patch is huuuge. It would be nice if you could split it, if
> possible...

Ok, I'll look at how to make this a bit more manageable.

Thanks,
Tom

> 
> Thanks.
>