linux-kernel - [PATCH v2 4/5] KVM: guest_memfd: add support for userfaultfd minor

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Message-ID: <20250402160721.97596-5-kalyazin@amazon.com>
Date: Wed, 2 Apr 2025 16:07:20 +0000
From: Nikita Kalyazin <kalyazin@...zon.com>
To: <akpm@...ux-foundation.org>, <pbonzini@...hat.com>, <shuah@...nel.org>
CC: <kvm@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<lorenzo.stoakes@...cle.com>, <david@...hat.com>, <ryan.roberts@....com>,
	<quic_eberman@...cinc.com>, <jthoughton@...gle.com>, <peterx@...hat.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 v2 4/5] KVM: guest_memfd: add support for userfaultfd minor

Add support for sending a pagefault event if userfaultfd is registered.
Only page minor event is currently supported.

Signed-off-by: Nikita Kalyazin <kalyazin@...zon.com>
---
 virt/kvm/guest_memfd.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 26b1734b9623..92d3e6b51dc2 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -4,6 +4,9 @@
 #include <linux/kvm_host.h>
 #include <linux/pagemap.h>
 #include <linux/anon_inodes.h>
+#ifdef CONFIG_KVM_PRIVATE_MEM
+#include <linux/userfaultfd_k.h>
+#endif /* CONFIG_KVM_PRIVATE_MEM */
 
 #include "kvm_mm.h"
 
@@ -380,6 +383,13 @@ static vm_fault_t kvm_gmem_fault(struct vm_fault *vmf)
 		kvm_gmem_mark_prepared(folio);
 	}
 
+	if (userfaultfd_minor(vmf->vma) &&
+	    !(vmf->flags & FAULT_FLAG_NO_USERFAULT_MINOR)) {
+		folio_unlock(folio);
+		filemap_invalidate_unlock_shared(inode->i_mapping);
+		return handle_userfault(vmf, VM_UFFD_MINOR);
+	}
+
 	vmf->page = folio_file_page(folio, vmf->pgoff);
 
 out_folio:
-- 
2.47.1