linux-kernel - Re: [RFC Part1 PATCH v3 07/17] x86/mm: Include SEV for encryption memory attribute changes

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Date:   Thu, 17 Aug 2017 13:21:39 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     David Laight <David.Laight@...LAB.COM>,
        'Borislav Petkov' <bp@...e.de>,
        Brijesh Singh <brijesh.singh@....com>
Cc:     "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        Radim Krcmár <rkrcmar@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        David Howells <dhowells@...hat.com>,
        Paul Mackerras <paulus@...ba.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Christoph Lameter <cl@...ux.com>,
        Jonathan Corbet <corbet@....net>,
        "x86@...nel.org" <x86@...nel.org>, Piotr Luc <piotr.luc@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Airlie <airlied@...hat.com>,
        Laura Abbott <labbott@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tony Luck <tony.luck@...el.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Tejun Heo <tj@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>
Subject: Re: [RFC Part1 PATCH v3 07/17] x86/mm: Include SEV for encryption
 memory attribute changes

On 7/28/2017 3:47 AM, David Laight wrote:
> From: Borislav Petkov
>> Sent: 27 July 2017 15:59
>> On Mon, Jul 24, 2017 at 02:07:47PM -0500, Brijesh Singh wrote:
>>> From: Tom Lendacky <thomas.lendacky@....com>
>>>
>>> The current code checks only for sme_active() when determining whether
>>> to perform the encryption attribute change.  Include sev_active() in this
>>> check so that memory attribute changes can occur under SME and SEV.
>>>
>>> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
>>> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
>>> ---
>>>   arch/x86/mm/pageattr.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
>>> index dfb7d65..b726b23 100644
>>> --- a/arch/x86/mm/pageattr.c
>>> +++ b/arch/x86/mm/pageattr.c
>>> @@ -1781,8 +1781,8 @@ static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
>>>   	unsigned long start;
>>>   	int ret;
>>>
>>> -	/* Nothing to do if the SME is not active */
>>> -	if (!sme_active())
>>> +	/* Nothing to do if SME and SEV are not active */
>>> +	if (!sme_active() && !sev_active())
>>
>> This is the second place which does
>>
>> 	if (!SME && !SEV)
>>
>> I wonder if, instead of sprinking those, we should have a
>>
>> 	if (mem_enc_active())
>>
>> or so which unifies all those memory encryption logic tests and makes
>> the code more straightforward for readers who don't have to pay
>> attention to SME vs SEV ...
> 
> If any of the code paths are 'hot' it would make sense to be checking
> a single memory location.

The function would check a single variable/memory location and making it
an inline function would accomplish that.

Thanks,
Tom

> 
> 	David
>