Re: [PATCH v14 02/21] KVM: Rename CONFIG_KVM_GENERIC_PRIVATE_MEM to CONFIG_KVM_GENERIC_GMEM_POPULATE

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 7/16/2025 4:11 PM, Fuad Tabba wrote:
> On Wed, 16 Jul 2025 at 05:09, Xiaoyao Li<xiaoyao.li@intel.com> wrote:
>> On 7/15/2025 5:33 PM, Fuad Tabba wrote:
>>> The original name was vague regarding its functionality. This Kconfig
>>> option specifically enables and gates the kvm_gmem_populate() function,
>>> which is responsible for populating a GPA range with guest data.
>> Well, I disagree.
>>
>> The config KVM_GENERIC_PRIVATE_MEM was introduced by commit 89ea60c2c7b5
>> ("KVM: x86: Add support for "protected VMs" that can utilize private
>> memory"), which is a convenient config for vm types that requires
>> private memory support, e.g., SNP, TDX, and KVM_X86_SW_PROTECTED_VM.
>>
>> It was commit e4ee54479273 ("KVM: guest_memfd: let kvm_gmem_populate()
>> operate only on private gfns") that started to use
>> CONFIG_KVM_GENERIC_PRIVATE_MEM gates kvm_gmem_populate() function. But
>> CONFIG_KVM_GENERIC_PRIVATE_MEM is not for kvm_gmem_populate() only.
>>
>> If using CONFIG_KVM_GENERIC_PRIVATE_MEM to gate kvm_gmem_populate() is
>> vague and confusing, we can introduce KVM_GENERIC_GMEM_POPULATE to gate
>> kvm_gmem_populate() and select KVM_GENERIC_GMEM_POPULATE under
>> CONFIG_KVM_GENERIC_PRIVATE_MEM.
>>
>> Directly replace CONFIG_KVM_GENERIC_PRIVATE_MEM with
>> KVM_GENERIC_GMEM_POPULATE doesn't look correct to me.
> I'll quote David's reply to an earlier version of this patch [*]:

It's not related to my concern.

My point is that CONFIG_KVM_GENERIC_PRIVATE_MEM is used for selecting 
the private memory support. Rename it to KVM_GENERIC_GMEM_POPULATE is 
not correct.

Current code uses CONFIG_KVM_GENERIC_PRIVATE_MEM to gate 
kvm_gmem_populate() because kvm_gmem_populate() requires both gmem and 
memory attributes support and CONFIG_KVM_GENERIC_PRIVATE_MEM can ensure 
it. But CONFIG_KVM_GENERIC_PRIVATE_MEM was not only for gating 
kvm_gmem_populate().

>>> I'm curious what generic means in this name?
>> That an architecture wants to use the generic version and not provide
>> it's own alternative implementation.
>>
>> We frequently use that term in this context, see GENERIC_IOREMAP as one
>> example.
> [*]https://lore.kernel.org/all/b6355951-5f9d-4ca9-850f-79e767d8caa2@redhat.com/
> 
> Thanks,
> /fuad