linux-kernel - Re: [PATCH v6 6/6] drivers/node: Show in sysfs node's crypto capabilities

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Message-ID: <ec9e29a4-0d2b-1423-d92e-6f025b56f8cc@amd.com>
Date:   Fri, 4 Feb 2022 10:23:22 -0600
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     Tom Lendacky <thomas.lendacky@....com>,
        Martin Fernandez <martin.fernandez@...ypsium.com>
Cc:     linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, linux-mm@...ck.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        ardb@...nel.org, dvhart@...radead.org, andy@...radead.org,
        gregkh@...uxfoundation.org, rafael@...nel.org, rppt@...nel.org,
        akpm@...ux-foundation.org, daniel.gutson@...ypsium.com,
        hughsient@...il.com, alex.bazhaniuk@...ypsium.com,
        alison.schofield@...el.com, keescook@...omium.org
Subject: Re: [PATCH v6 6/6] drivers/node: Show in sysfs node's crypto
 capabilities

On 2/4/2022 09:59, Tom Lendacky wrote:
> On 2/4/22 07:21, Martin Fernandez wrote:
>> On 2/4/22, Limonciello, Mario <mario.limonciello@....com> wrote:
>>> On 2/3/2022 10:43, Martin Fernandez wrote:
>>>> +static ssize_t crypto_capable_show(struct device *dev,
>>>> +                   struct device_attribute *attr, char *buf)
>>>> +{
>>>> +    struct pglist_data *pgdat = NODE_DATA(dev->id);
>>>> +
>>>> +    return sysfs_emit(buf, "%d\n", pgdat->crypto_capable);
>>>
>>> As there is interest in seeing these capabilities from userspace, it
>>> seems like a logical time to also expose a `crypto_active` attribute.
>>
>> I planned to do something similar to this, but to show (or actually
>> hide if inactive) tme in cpuinfo, just as Borislav Petkov suggested a
>> few versions back.
>>
>> https://lore.kernel.org/linux-efi/YXrnkxgdjWbcPlJA@zn.tnic/

As Tom agreed in previous post, Boris is mistaken here.  I just double 
checked on my side on a workstation that supports SME and comparing 
/proc/cpuinfo before and after SME is enabled via mem_encrypt=on.  I 
confirmed that nothing changed.

>>
>>> Then userspace can make a judgement call if the system supports crypto
>>> memory (`crypto_capable`) and then also whether or not it's been turned
>>> on (`crypto_active`).
>>>
>>> `crypto_active` could be detected with some existing support in the
>>> kernel of `mem_encrypt_active()`.  This will then work for a variety of
>>> architectures too that offer `mem_encrypt_active()`.
>>
>> I need a hand with this, I grepped for mem_encrypt_active and nothing
>> showed up...
> 
> The mem_encrypt_active() function has been replaced by 
> cc_platform_has(CC_ATTR_MEM_ENCRYPT).

Yes, thanks for correcting it .

> 
>>
>>> As it stands today the only reliable way to tell from userspace (at
>>> least for AMD's x86 implementation) is by grepping the system log for
>>> the line "AMD Memory Encryption Features active".
>>
>> Isn't enough to grep for sme/sev in cpuinfo?
> 
> No, it's not enough. Cpuinfo shows a processors capabilities and not 
> necessarily whether that capability is being used.
> 
> Thanks,
> Tom

Tom,

Maybe some sysfs file(s) directly from cc_platform.c makes more sense then?