linux-kernel - [PATCH v1 03/13] KVM: Allow late setting of KVM_MEM_USERFAULT on guest

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Message-ID: <20241204191349.1730936-4-jthoughton@google.com>
Date: Wed,  4 Dec 2024 19:13:38 +0000
From: James Houghton <jthoughton@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>
Cc: Jonathan Corbet <corbet@....net>, Marc Zyngier <maz@...nel.org>, 
	Oliver Upton <oliver.upton@...ux.dev>, 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>, Wang@...gle.com, Wei W <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 v1 03/13] KVM: Allow late setting of KVM_MEM_USERFAULT on
 guest_memfd memslot

Currently guest_memfd memslots can only be deleted. Slightly change the
logic to allow KVM_MR_FLAGS_ONLY changes when the only flag being
changed is KVM_MEM_USERFAULT.

Signed-off-by: James Houghton <jthoughton@...gle.com>
---
 virt/kvm/kvm_main.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 23fa3e911c4e..fa851704db94 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2009,9 +2009,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
 			return -EINVAL;
 	} else { /* Modify an existing slot. */
-		/* Private memslots are immutable, they can only be deleted. */
-		if (mem->flags & KVM_MEM_GUEST_MEMFD)
-			return -EINVAL;
 		if ((mem->userspace_addr != old->userspace_addr) ||
 		    (npages != old->npages) ||
 		    ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
@@ -2025,6 +2022,16 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			return 0;
 	}
 
+	/*
+	 * Except for being able to set KVM_MEM_USERFAULT, private memslots are
+	 * immutable, they can only be deleted.
+	 */
+	if (mem->flags & KVM_MEM_GUEST_MEMFD &&
+	    !(change == KVM_MR_CREATE ||
+	      (change == KVM_MR_FLAGS_ONLY &&
+	       (mem->flags ^ old->flags) == KVM_MEM_USERFAULT)))
+		return -EINVAL;
+
 	if ((change == KVM_MR_CREATE || change == KVM_MR_MOVE) &&
 	    kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages))
 		return -EEXIST;
@@ -2040,7 +2047,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	new->npages = npages;
 	new->flags = mem->flags;
 	new->userspace_addr = mem->userspace_addr;
-	if (mem->flags & KVM_MEM_GUEST_MEMFD) {
+	if (mem->flags & KVM_MEM_GUEST_MEMFD && change == KVM_MR_CREATE) {
 		r = kvm_gmem_bind(kvm, new, mem->guest_memfd, mem->guest_memfd_offset);
 		if (r)
 			goto out;
-- 
2.47.0.338.g60cca15819-goog