linux-kernel - Re: [PATCH v8 0/8] x86: Show in sysfs if a memory node is able to do encryption

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Date:   Fri, 6 May 2022 08:32:29 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Borislav Petkov <bp@...en8.de>,
        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, 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,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        Ben Widawsky <ben.widawsky@...el.com>,
        "Huang, Kai" <kai.huang@...el.com>
Subject: Re: [PATCH v8 0/8] x86: Show in sysfs if a memory node is able to do
 encryption

On 5/6/22 05:44, Borislav Petkov wrote:
>> Dave Hansen pointed those out in a previuos patch serie, here is the
>> quote:
>>
>>> CXL devices will have normal RAM on them, be exposed as "System RAM" and
>>> they won't have encryption capabilities.  I think these devices were
>>> probably the main motivation for EFI_MEMORY_CPU_CRYPTO.
> So this would mean that if a system doesn't have CXL devices and has
> TME/SME/SEV-* enabled, then it is running with encrypted memory.
> 
> Which would then also mean, you don't need any of that code - you only
> need to enumerate CXL devices which, it seems, do not support memory
> encryption, and then state that memory encryption is enabled on the
> whole system, except for the memory of those devices.

CXL devices are just the easiest example to explain, but they are not
the only problem.

For example, Intel NVDIMMs don't support TDX (or MKTME with integrity)
since TDX requires integrity protection and NVDIMMs don't have metadata
space available.

Also, if this were purely a CXL problem, I would have expected this to
have been dealt with in the CXL spec alone.  But, this series is
actually driven by an ACPI spec.  That tells me that we'll see these
mismatched encryption capabilities in many more places than just CXL
devices.