Re: [PATCH v10 07/41] KVM: guest_memfd: Stub in ability to enable in-place shared<=>private conversion

[...snip...]

quoted

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I'm looking at the doc of KVM_SET_USER_MEMORY_REGION2, which reads

# When mapping a gfn into the guest, KVM selects shared vs. private, i.e consumes
# userspace_addr vs. guest_memfd, based on the gfn's KVM_MEMORY_ATTRIBUTE_PRIVATE
# state.  At VM creation time, all memory is shared, i.e. the PRIVATE attribute
# is '0' for all gfns.  Userspace can control whether memory is shared/private by
# toggling KVM_MEMORY_ATTRIBUTE_PRIVATE via KVM_SET_MEMORY_ATTRIBUTES as needed.

I'm not sure how this snippet from the documentation connects with what
you'd like changed.

It's flat out wrong once in-place conversion lands, because it assumes PRIVATE
is tracked per-VM.  Something like this?

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 4eb7e75a7473..c9769e5e7329 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst

@@ -6383,9 +6383,12 @@ on-demand.

 When mapping a gfn into the guest, KVM selects shared vs. private, i.e consumes
 userspace_addr vs. guest_memfd, based on the gfn's KVM_MEMORY_ATTRIBUTE_PRIVATE
-state.  At VM creation time, all memory is shared, i.e. the PRIVATE attribute
-is '0' for all gfns.  Userspace can control whether memory is shared/private by
+state.  If in-place conversion is disabled, i.e. PRIVATE is tracked per-VM,
+then at VM creation time, all memory is shared, i.e. the PRIVATE attribute is
+'0' for all gfns.  Userspace can control whether memory is shared/private by
 toggling KVM_MEMORY_ATTRIBUTE_PRIVATE via KVM_SET_MEMORY_ATTRIBUTES as needed.
+If in-place conversion is enabled, then the starting PRIVATE vs. SHARED state
+of a gfn is determined by the relevant guest_memfd instance.

 S390:
 ^^^^^