Re: [PATCH v10 20/41] KVM: Let userspace disable per-VM mem attributes, enable per-gmem attributes

[Ackerley Tng]

"David Hildenbrand (Arm)" <david@xxxxxxxxxx> writes:

> On 8/7/26 23:52, Ackerley Tng via B4 Relay wrote:
>> From: Ackerley Tng <ackerleytng@xxxxxxxxxx>
>>
>>
>> [...snip...]
>>
>> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
>> index abb108886733a..2c3c22aeafa54 100644
>> --- a/arch/x86/kvm/Kconfig
>> +++ b/arch/x86/kvm/Kconfig
>> @@ -81,13 +81,21 @@ config KVM_WERROR
>>  	  If in doubt, say "N".
>>
>>  config KVM_VM_MEMORY_ATTRIBUTES
>> -	bool
>> +	bool "Enable per-VM PRIVATE vs. SHARED attributes (for CoCo VMs)"
>> +	depends on KVM_SW_PROTECTED_VM || KVM_INTEL_TDX || KVM_AMD_SEV
>> +	help
>> +	  Enable support for tracking PRIVATE vs. SHARED memory using per-VM
>> +	  memory attributes.  Using per-VM attributes is deprecated in favor of
>> +	  tracking PRIVATE state in guest_memfd.  Select this if you need to run
>> +	  CoCo VMs using a VMM that doesn't support guest_memfd memory
>> +	  attributes.
>> +
>> +	  If unsure, say N.
>
> Hm, does that imply that a distribution that must support both, cannot ship a
> single kernel?
>

Did you mean this as a documentation comment? Should the above read:

	help
	  Enable support for tracking PRIVATE vs. SHARED memory using per-VM
	  memory attributes.  Using per-VM attributes is deprecated in favor of
	  tracking PRIVATE state in guest_memfd.  Select this if you need to run
	  CoCo VMs using a VMM that doesn't support guest_memfd memory
-	  attributes.
+	  attributes. Select this to defer selection of where PRIVATE vs. SHARED
+	  attributes are tracked to KVM module load time, where
+	  gmem_in_place_conversion can be specified as a module parameter.

	  If unsure, say N.

I think we should do _without_ the above clarification since using VM
memory attributes for shared/private status is intended to be
deprecated.

Is it fair to say distributions should not support both, and if they
_must_ support both, they need to read code to figure this out?

> --
> Cheers,
>
> David