KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 51 insertions, 0 deletions

diff --git a/drivers/iommu/iommu-debugfs.c b/drivers/iommu/iommu-debugfs.c
new file mode 100644
index 000000000..f03548942
--- /dev/null
+++ b/drivers/iommu/iommu-debugfs.c
@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * IOMMU debugfs core infrastructure
+ *
+ * Copyright (C) 2018 Advanced Micro Devices, Inc.
+ *
+ * Author: Gary R Hook <gary.hook@amd.com>
+ */
+
+#include <linux/pci.h>
+#include <linux/iommu.h>
+#include <linux/debugfs.h>
+
+struct dentry *iommu_debugfs_dir;
+EXPORT_SYMBOL_GPL(iommu_debugfs_dir);
+
+/**
+ * iommu_debugfs_setup - create the top-level iommu directory in debugfs
+ *
+ * Provide base enablement for using debugfs to expose internal data of an
+ * IOMMU driver. When called, this function creates the
+ * /sys/kernel/debug/iommu directory.
+ *
+ * Emit a strong warning at boot time to indicate that this feature is
+ * enabled.
+ *
+ * This function is called from iommu_init; drivers may then use
+ * iommu_debugfs_dir to instantiate a vendor-specific directory to be used
+ * to expose internal data.
+ */
+void iommu_debugfs_setup(void)
+{
+	if (!iommu_debugfs_dir) {
+		iommu_debugfs_dir = debugfs_create_dir("iommu", NULL);
+		pr_warn("\n");
+		pr_warn("*************************************************************\n");
+		pr_warn("**     NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE    **\n");
+		pr_warn("**                                                         **\n");
+		pr_warn("**  IOMMU DebugFS SUPPORT HAS BEEN ENABLED IN THIS KERNEL  **\n");
+		pr_warn("**                                                         **\n");
+		pr_warn("** This means that this kernel is built to expose internal **\n");
+		pr_warn("** IOMMU data structures, which may compromise security on **\n");
+		pr_warn("** your system.                                            **\n");
+		pr_warn("**                                                         **\n");
+		pr_warn("** If you see this message and you are not debugging the   **\n");
+		pr_warn("** kernel, report this immediately to your vendor!         **\n");
+		pr_warn("**                                                         **\n");
+		pr_warn("**     NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE    **\n");
+		pr_warn("*************************************************************\n");
+	}
+}