[PATCH v8 24/46] KVM: guest_memfd: Make in-place conversion the default
From: Ackerley Tng via B4 Relay <devnull+ackerleytng.google.com@kernel.org>
Date: 2026-06-19 00:31:49
Also in:
b4-sent, kvm, linux-coco, linux-kselftest, linux-mm, linux-trace-kernel, lkml
Subsystem:
kernel virtual machine (kvm), kernel virtual machine for x86 (kvm/x86), the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Paolo Bonzini, Sean Christopherson, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
From: Ackerley Tng <redacted> Make in-place conversion the default if the arch has private mem. The default can be overridden at compile type by enabling CONFIG_KVM_VM_MEMORY_ATTRIBUTES, or at KVM load time through a module parameter. In-place conversion also implies tracking a guest's private/shared state in guest_memfd. To avoid inconsistencies in the way memory attributes are tracked between the per-VM or by guest_memfd, make the module_param read-only (0444). Document that using per-VM attributes for tracking private/shared state of guest memory is deprecated in favor of tracking in guest_memfd. Warn if the admin sets gmem_in_place_conversion as false when CONFIG_KVM_VM_MEMORY_ATTRIBUTES is not enabled. Add warning in the code path where guest memory is populated for a CoCo VM, since that's the earliest point in a CoCo VM's lifecycle where memory attributes are queried. Unlike other query sites, this site is exclusively used by CoCo VMs. Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/x86/kvm/Kconfig | 7 ++++++- virt/kvm/guest_memfd.c | 5 +++++ virt/kvm/kvm_main.c | 3 ++- 3 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index c28393dc664eb..a3c189d765150 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig@@ -85,7 +85,12 @@ config KVM_VM_MEMORY_ATTRIBUTES bool "Enable per-VM PRIVATE vs. SHARED attributes (for CoCo VMs)" help Enable support for tracking PRIVATE vs. SHARED memory using per-VM - memory attributes. + memory attributes. Using per-VM attributes are 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"
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 86c9f5b0863cb..5cb73543c03c8 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c@@ -1193,10 +1193,15 @@ static bool kvm_gmem_range_is_private(struct file *file, pgoff_t index, { struct maple_tree *mt = &GMEM_I(file_inode(file))->attributes; +#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); +#else + if (WARN_ON_ONCE(!gmem_in_place_conversion)) + return false; +#endif return kvm_gmem_range_has_attributes(mt, index, nr_pages, KVM_MEMORY_ATTRIBUTE_PRIVATE);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index dd1d18a1d2f68..46e92b5dc3804 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c@@ -102,7 +102,8 @@ 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); +module_param(gmem_in_place_conversion, bool, 0444); EXPORT_SYMBOL_FOR_KVM_INTERNAL(gmem_in_place_conversion); #endif
--
2.55.0.rc0.738.g0c8ab3ebcc-goog