linux-kernel - [PATCH 3/4] KVM: allow KVM_GUEST_MEMFD

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Message-ID: <20241024095429.54052-4-kalyazin@amazon.com>
Date: Thu, 24 Oct 2024 09:54:28 +0000
From: Nikita Kalyazin <kalyazin@...zon.com>
To: <pbonzini@...hat.com>, <corbet@....net>, <kvm@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: <jthoughton@...gle.com>, <brijesh.singh@....com>, <michael.roth@....com>,
	<graf@...zon.de>, <jgowans@...zon.com>, <roypat@...zon.co.uk>,
	<derekmn@...zon.com>, <nsaenz@...zon.es>, <xmarcalx@...zon.com>,
	<kalyazin@...zon.com>
Subject: [PATCH 3/4] KVM: allow KVM_GUEST_MEMFD_POPULATE in another mm

Allow calling KVM_GUEST_MEMFD_POPULATE ioctl by the process that does
not own the KVM context.
This is to enable guest_memfd population by a non-VMM process that is
useful for isolation of the memory management logic from the VMM for
security and performance reasons.

Signed-off-by: Nikita Kalyazin <kalyazin@...zon.com>
---
 virt/kvm/kvm_main.c | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e5bd2c0031bf..eb626c4bf4d7 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -5159,8 +5159,25 @@ static long kvm_vm_ioctl(struct file *filp,
 	void __user *argp = (void __user *)arg;
 	int r;
 
-	if (kvm->mm != current->mm || kvm->vm_dead)
+	if (kvm->vm_dead)
 		return -EIO;
+
+#ifdef CONFIG_KVM_PRIVATE_MEM
+	if (ioctl == KVM_GUEST_MEMFD_POPULATE) {
+		struct kvm_guest_memfd_populate populate;
+
+		r = -EFAULT;
+		if (copy_from_user(&populate, argp, sizeof(populate)))
+			goto out;
+
+		r = kvm_gmem_guest_memfd_populate(kvm, &populate);
+		goto out;
+	}
+#endif
+
+	if (kvm->mm != current->mm)
+		return -EIO;
+
 	switch (ioctl) {
 	case KVM_CREATE_VCPU:
 		r = kvm_vm_ioctl_create_vcpu(kvm, arg);
@@ -5383,16 +5400,6 @@ static long kvm_vm_ioctl(struct file *filp,
 		r = kvm_gmem_create(kvm, &guest_memfd);
 		break;
 	}
-	case KVM_GUEST_MEMFD_POPULATE: {
-		struct kvm_guest_memfd_populate populate;
-
-		r = -EFAULT;
-		if (copy_from_user(&populate, argp, sizeof(populate)))
-			goto out;
-
-		r = kvm_gmem_guest_memfd_populate(kvm, &populate);
-		break;
-	}
 #endif
 	default:
 		r = kvm_arch_vm_ioctl(filp, ioctl, arg);
-- 
2.40.1