linux-kernel - [PATCH v3 07/15] KVM: Enable and advertise support for KVM userfault exits

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Message-ID: <20250618042424.330664-8-jthoughton@google.com>
Date: Wed, 18 Jun 2025 04:24:16 +0000
From: James Houghton <jthoughton@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>, 
	Oliver Upton <oliver.upton@...ux.dev>
Cc: Jonathan Corbet <corbet@....net>, Marc Zyngier <maz@...nel.org>, Yan Zhao <yan.y.zhao@...el.com>, 
	James Houghton <jthoughton@...gle.com>, Nikita Kalyazin <kalyazin@...zon.com>, 
	Anish Moorthy <amoorthy@...gle.com>, Peter Gonda <pgonda@...gle.com>, Peter Xu <peterx@...hat.com>, 
	David Matlack <dmatlack@...gle.com>, wei.w.wang@...el.com, kvm@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev
Subject: [PATCH v3 07/15] KVM: Enable and advertise support for KVM userfault exits

Now that all architectures (arm64 and x86) that utilize "generic" page
faults also support userfault exits, advertise support for
KVM_CAP_USERFAULT and let userspace set KVM_MEM_USERFAULT in memslots.

Signed-off-by: James Houghton <jthoughton@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 include/uapi/linux/kvm.h | 1 +
 virt/kvm/kvm_main.c      | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index e3b871506ec85..0ba265f99f033 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -937,6 +937,7 @@ struct kvm_enable_cap {
 #define KVM_CAP_ARM_EL2 240
 #define KVM_CAP_ARM_EL2_E2H0 241
 #define KVM_CAP_RISCV_MP_STATE_RESET 242
+#define KVM_CAP_USERFAULT 243
 
 struct kvm_irq_routing_irqchip {
 	__u32 irqchip;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index bef6760cd1c0e..2962be09d5ebf 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1604,6 +1604,9 @@ static int check_memory_region_flags(struct kvm *kvm,
 	    !(mem->flags & KVM_MEM_GUEST_MEMFD))
 		valid_flags |= KVM_MEM_READONLY;
 
+	if (IS_ENABLED(CONFIG_KVM_GENERIC_PAGE_FAULT))
+		valid_flags |= KVM_MEM_USERFAULT;
+
 	if (mem->flags & ~valid_flags)
 		return -EINVAL;
 
@@ -4881,6 +4884,9 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
 	case KVM_CAP_CHECK_EXTENSION_VM:
 	case KVM_CAP_ENABLE_CAP_VM:
 	case KVM_CAP_HALT_POLL:
+#ifdef CONFIG_KVM_GENERIC_PAGE_FAULT
+	case KVM_CAP_USERFAULT:
+#endif
 		return 1;
 #ifdef CONFIG_KVM_MMIO
 	case KVM_CAP_COALESCED_MMIO:
-- 
2.50.0.rc2.692.g299adb8693-goog