linux-kernel - Re: [PATCH] Use 'imply' with SEV Kconfig CRYPTO dependencies

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Date:   Tue, 19 Jun 2018 14:22:53 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Borislav Petkov <bp@...e.de>
Cc:     brijesh.singh@....com,
        Richard Weinberger <richard.weinberger@...il.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@....com>,
        Tom Lendacky <thomas.lendacky@....com>, x86@...nel.org,
        kvm <kvm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, felix@...dspaten.org
Subject: Re: [PATCH] Use 'imply' with SEV Kconfig CRYPTO dependencies

Hi Boris,


On 06/19/2018 04:46 AM, Borislav Petkov wrote:
> On Thu, Jun 14, 2018 at 07:08:26AM -0500, Brijesh Singh wrote:
>> I think depends should look like this:
>>
>> config KVM_AMD_SEV
>>      def_bool y
>>      bool "AMD Secure Encrypted Virtualization (SEV) support"
>>      depends KVM_AMD && X86_64
>>      depends CRYPTO_DEV_SP_PSP && !(KVM_AMD=y && CRYPTO_DEV_CCP_DD=m)
> 
> CRYPTO_DEV_CCP_DD - this still doesn't belong here. KVM_AMD_SEV doesn't
> care about what kind of functionality the PSP needs to function and
> select it - it should only depend on a single symbol.
> 


It would be nice to have a single depends. But the main issue is, PSP 
support is provided through the ccp driver (aka CRYPTO_DEV_CCP_DD). 
Hence KVM_AMD_SEV need to have some level of dependency with ccp driver. 
This is to ensure that the ccp was 'y' when kvm-amd=y for SEV to work.


> Now, you can add a separate CRYPTO .config item which collects all
> required functionality for SEV guests and have KVM_AMD_SEV depend
> on that. Or a similar solution. But not have KVM_AMD_SEV poke into
> CRYPTO...PSP dependencies because it doesn't need to know about it.
> 


I am sorry but I am not able to follow you on how creating a separate 
CRYPTO .config item will solve this problem. Creating a separate config 
will be useful if we are okay with calling 'select' from kvm (i.e if 
kvm-amd is 'y' then all the symbols from crypto will be 'y').

I looked at other drivers where they have similar situation and it seems 
like solution is same as what I have used above.


-Brijesh