Re: [PATCH v14 02/22] KVM: selftests: Update kvm_init_vm_address_properties() for TDX

[Ackerley Tng]

"Edgecombe, Rick P" <rick.p.edgecombe@xxxxxxxxx> writes:

> On Wed, 2026-07-22 at 23:13 +0000, Lisa Wang wrote:
>> From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
>>
>> Initialize the TDX S-bit and the GPA tag mask in
>> kvm_init_vm_address_properties() for TDX VMs, similar to how the C-bit
>> is initialized for SEV VMs.
>>
>> The TDX S-bit is used to distinguish between shared and private guest
>> physical addresses. Its position is determined by the guest physical
>> address width, which is either 48 or 52 bits for current TDX
>> implementations.
>
> Since S-bit=1 means shared and C-bit=1 means private, we can't have a single
> bit. I'd justify why a second field is needed.

The s_bit field was introduced prior to this patch series, so I think
the patch introducing the s_bit field should have justified the addition
of this second field.

Did you mean that we should add something related to "Since S-bit=1
means shared and C-bit=1 means private, we can't have a single bit." in
the commit message to reiterate/as a refresher?

> For "untagging" GPAs we could
> have a single field, but there are other usages?
>

I think this part in __virt_pg_map() requires separate fields, are you
requesting to only retain one of the c_bit/s_bit vs gpa_tag_mask?

	if (vm_is_gpa_protected(vm, gpa))
		*pte |= PTE_C_BIT_MASK(mmu);
	else
		*pte |= PTE_S_BIT_MASK(mmu);

I think if there's any unification/simplification required among these
fields, perhaps that can be left to another series.

>>
>> Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
>> Co-developed-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
>> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
>> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
>> Co-developed-by: Sagi Shahar <sagis@xxxxxxxxxx>
>> Signed-off-by: Sagi Shahar <sagis@xxxxxxxxxx>
>> Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
>> Signed-off-by: Lisa Wang <wyihan@xxxxxxxxxx>
>> Reviewed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
>> ---
> Nit: these are not ordered correctly. I think KVM prefers the order in:
> Documentation/process/maintainer-tip.rst
>
> But I think at least the RBs can be grouped together. Also... can't really point
> fingers here, but that is a fair amount of of patch history.

I was also involved in some earlier revision of this series, tracing
this history is not trivial...

For this series, given the long history and many handoffs, shall we help
Lisa out by explicitly requesting to be credited on specific patches?
Emailing either Lisa/Ackerley privately or on-list is fine :)