Re: [PATCH 2/2] x86/sev: Make SEV_STATUS available via SYSFS

[Dave Hansen <dave.hansen@intel.com>]

On 3/12/25 08:07, Joerg Roedel wrote:
> Hi Dave,
> 
> On Wed, Mar 12, 2025 at 07:57:31AM -0700, Dave Hansen wrote:
>> Do we really want to just plumb the raw MSR out to userspace? Users
>> would still need to parse the thing, so it's not _really_ human readable.
> 
> I agree that this is not really human readable. On the other side SYSFS
> is more an interface targeted for tools than optimized for human
> readability (see the one-datum-per-file rule).

Right, but I think it's also intended to be independent and not
*require* tools to make sense of the output. A raw MSR requires tooling
or someone sitting there with the hardware docs to make sense of it.

That's why we have things like:

	/sys/kernel/mm/transparent_hugepage/enabled

that tell you:

	[always] madvise never

as opposed to the old style in:

	/proc/sys/vm/zone_reclaim_mode

which require you to go read the docs and figure out what 0/1/2 mean.

> The actual use-case (and the reason for these patches) of the sev_status
> file is to provide a better and more secure interface than /dev/msr to a
> tool named snpguest.

Let's draw this out to its natural conclusion. There are also a bunch of
TDX attributes that tell you about the capabilities of the VM and the
TDX module.

Should we have:

	/sys/devices/system/cpu/tdx/tdx_attributes

which just dumps out the raw register values that come back from the
TDCALL? Then we'll go write a tdxguest tool to parse those values.