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

From: Ackerley Tng <redacted>

Make gmem_in_place_conversion a module parameter so that userspace can
configure enable or disable the use of VM-level memory attributes. The
module parameter is only available if CONFIG_KVM_VM_MEMORY_ATTRIBUTES is
enabled.

To avoid inconsistencies in the way memory attributes are tracked in KVM
and guest_memfd, the vm_memory_attributes module_param is made
read-only (0444).

Since selecting CONFIG_KVM_VM_MEMORY_ATTRIBUTES disables in-place
conversion, actually make CONFIG_KVM_VM_MEMORY_ATTRIBUTES selectable. Make
the config only selectable for (CoCo) VM types that might use
vm_memory_attributes.

Since memory attributes are trackable in guest_memfd, the concept of having
private memory is no longer dependent on
CONFIG_KVM_VM_MEMORY_ATTRIBUTES. Define kvm_arch_has_private_mem() based on
platform config, so that having private memory is dependent on (CoCo) VM
type.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Fuad Tabba <redacted>
Tested-by: Shivank Garg <redacted>
[Define module_param only if CONFIG_KVM_VM_MEMORY_ATTRIBUTES is enabled]
Suggested-by: Xiaoyao Li <redacted>
Reviewed-by: Xiaoyao Li <redacted>
Signed-off-by: Ackerley Tng <redacted>
---
 arch/x86/include/asm/kvm_host.h |  4 +++-
 arch/x86/kvm/Kconfig            | 14 ++++++++++----
 virt/kvm/kvm_main.c             |  5 ++++-
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 497da6aaf2942..bb2c1ade62cf9 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h

@@ -1851,7 +1851,9 @@ enum kvm_intr_type {
 	((vcpu) && (vcpu)->arch.handling_intr_from_guest && \
 	 (!!in_nmi() == ((vcpu)->arch.handling_intr_from_guest == KVM_HANDLING_NMI)))
 
-#ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES
+#if defined(CONFIG_KVM_SW_PROTECTED_VM) ||	\
+    defined(CONFIG_KVM_INTEL_TDX) ||		\
+    defined(CONFIG_KVM_AMD_SEV)
 #define kvm_arch_has_private_mem(kvm) ((kvm)->arch.has_private_mem)
 #endif
 

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.