[PATCH v9 20/41] KVM: Let userspace disable per-VM mem attributes, enable per-gmem attributes

[Ackerley Tng via B4 Relay <devnull+ackerleytng.google.com@kernel.org>]

From: Ackerley Tng <ackerleytng@google.com>

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 <tabba@google.com>
Tested-by: Shivank Garg <shivankg@amd.com>
[Define module_param only if CONFIG_KVM_VM_MEMORY_ATTRIBUTES is enabled]
Suggested-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
 arch/x86/include/asm/kvm_host.h |  4 +++-
 arch/x86/kvm/Kconfig            | 14 ++++++++++----
 virt/kvm/guest_memfd.c          |  2 ++
 virt/kvm/kvm_main.c             |  5 ++++-
 4 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ceb2abf43b76f..766eb094eaae6 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1849,7 +1849,9 @@ 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.
 
 config KVM_SW_PROTECTED_VM
 	bool "Enable support for KVM software-protected VMs"
 	depends on EXPERT
 	depends on KVM_X86 && X86_64
-	select KVM_VM_MEMORY_ATTRIBUTES
 	help
 	  Enable support for KVM software-protected VMs.  Currently, software-
 	  protected VMs are purely a development and testing vehicle for
@@ -138,7 +146,6 @@ config KVM_INTEL_TDX
 	bool "Intel Trust Domain Extensions (TDX) support"
 	default y
 	depends on INTEL_TDX_HOST
-	select KVM_VM_MEMORY_ATTRIBUTES
 	select HAVE_KVM_ARCH_GMEM_POPULATE
 	help
 	  Provides support for launching Intel Trust Domain Extensions (TDX)
@@ -162,7 +169,6 @@ config KVM_AMD_SEV
 	depends on KVM_AMD && X86_64
 	depends on CRYPTO_DEV_SP_PSP && !(KVM_AMD=y && CRYPTO_DEV_CCP_DD=m)
 	select ARCH_HAS_CC_PLATFORM
-	select KVM_VM_MEMORY_ATTRIBUTES
 	select HAVE_KVM_ARCH_GMEM_CONVERT
 	select HAVE_KVM_ARCH_GMEM_RECLAIM
 	select HAVE_KVM_ARCH_GMEM_INVALIDATE
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index ea2752989f8bd..df67a6188aa99 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -1137,10 +1137,12 @@ static bool kvm_range_is_private(struct file *file, pgoff_t index,
 {
 	struct inode *inode = file_inode(file);
 
+#ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES
 	if (!gmem_in_place_conversion)
 		return kvm_range_has_vm_memory_attributes(kvm, gfn, gfn + nr_pages,
 							  KVM_MEMORY_ATTRIBUTE_PRIVATE,
 							  KVM_MEMORY_ATTRIBUTE_PRIVATE);
+#endif
 
 	return kvm_gmem_range_has_attributes(inode, index, nr_pages,
 					     KVM_MEMORY_ATTRIBUTE_PRIVATE);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e961cc297ba2a..eb9f433278d2f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -102,7 +102,10 @@ static bool __ro_after_init allow_unsafe_mappings;
 module_param(allow_unsafe_mappings, bool, 0444);
 
 #ifdef kvm_arch_has_private_mem
-bool __ro_after_init gmem_in_place_conversion = false;
+bool __ro_after_init gmem_in_place_conversion = !IS_ENABLED(CONFIG_KVM_VM_MEMORY_ATTRIBUTES);
+#ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES
+module_param(gmem_in_place_conversion, bool, 0444);
+#endif
 EXPORT_SYMBOL_FOR_KVM_INTERNAL(gmem_in_place_conversion);
 #endif
 

-- 
2.55.0.508.g3f0d502094-goog