KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 158 insertions, 0 deletions

diff --git a/io_uring/filetable.c b/io_uring/filetable.c
new file mode 100644
index 000000000..cb1838c9f
--- /dev/null
+++ b/io_uring/filetable.c
@@ -0,0 +1,158 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/file.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/nospec.h>
+#include <linux/io_uring.h>
+
+#include <uapi/linux/io_uring.h>
+
+#include "io_uring.h"
+#include "rsrc.h"
+#include "filetable.h"
+
+static int io_file_bitmap_get(struct io_ring_ctx *ctx)
+{
+	struct io_file_table *table = &ctx->file_table;
+	unsigned long nr = ctx->file_alloc_end;
+	int ret;
+
+	if (!table->bitmap)
+		return -ENFILE;
+
+	if (table->alloc_hint < ctx->file_alloc_start ||
+	    table->alloc_hint >= ctx->file_alloc_end)
+		table->alloc_hint = ctx->file_alloc_start;
+
+	do {
+		ret = find_next_zero_bit(table->bitmap, nr, table->alloc_hint);
+		if (ret != nr)
+			return ret;
+
+		if (table->alloc_hint == ctx->file_alloc_start)
+			break;
+		nr = table->alloc_hint;
+		table->alloc_hint = ctx->file_alloc_start;
+	} while (1);
+
+	return -ENFILE;
+}
+
+bool io_alloc_file_tables(struct io_ring_ctx *ctx, struct io_file_table *table,
+			  unsigned nr_files)
+{
+	if (io_rsrc_data_alloc(&table->data, nr_files))
+		return false;
+	table->bitmap = bitmap_zalloc(nr_files, GFP_KERNEL_ACCOUNT);
+	if (table->bitmap)
+		return true;
+	io_rsrc_data_free(ctx, &table->data);
+	return false;
+}
+
+void io_free_file_tables(struct io_ring_ctx *ctx, struct io_file_table *table)
+{
+	io_rsrc_data_free(ctx, &table->data);
+	bitmap_free(table->bitmap);
+	table->bitmap = NULL;
+}
+
+static int io_install_fixed_file(struct io_ring_ctx *ctx, struct file *file,
+				 u32 slot_index)
+	__must_hold(&ctx->uring_lock)
+{
+	struct io_rsrc_node *node;
+
+	if (io_is_uring_fops(file))
+		return -EBADF;
+	if (!ctx->file_table.data.nr)
+		return -ENXIO;
+	if (slot_index >= ctx->file_table.data.nr)
+		return -EINVAL;
+
+	node = io_rsrc_node_alloc(ctx, IORING_RSRC_FILE);
+	if (!node)
+		return -ENOMEM;
+
+	if (!io_reset_rsrc_node(ctx, &ctx->file_table.data, slot_index))
+		io_file_bitmap_set(&ctx->file_table, slot_index);
+
+	ctx->file_table.data.nodes[slot_index] = node;
+	io_fixed_file_set(node, file);
+	return 0;
+}
+
+int __io_fixed_fd_install(struct io_ring_ctx *ctx, struct file *file,
+			  unsigned int file_slot)
+{
+	bool alloc_slot = file_slot == IORING_FILE_INDEX_ALLOC;
+	int ret;
+
+	if (alloc_slot) {
+		ret = io_file_bitmap_get(ctx);
+		if (unlikely(ret < 0))
+			return ret;
+		file_slot = ret;
+	} else {
+		file_slot--;
+	}
+
+	ret = io_install_fixed_file(ctx, file, file_slot);
+	if (!ret && alloc_slot)
+		ret = file_slot;
+	return ret;
+}
+/*
+ * Note when io_fixed_fd_install() returns error value, it will ensure
+ * fput() is called correspondingly.
+ */
+int io_fixed_fd_install(struct io_kiocb *req, unsigned int issue_flags,
+			struct file *file, unsigned int file_slot)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+	int ret;
+
+	io_ring_submit_lock(ctx, issue_flags);
+	ret = __io_fixed_fd_install(ctx, file, file_slot);
+	io_ring_submit_unlock(ctx, issue_flags);
+
+	if (unlikely(ret < 0))
+		fput(file);
+	return ret;
+}
+
+int io_fixed_fd_remove(struct io_ring_ctx *ctx, unsigned int offset)
+{
+	struct io_rsrc_node *node;
+
+	if (unlikely(!ctx->file_table.data.nr))
+		return -ENXIO;
+	if (offset >= ctx->file_table.data.nr)
+		return -EINVAL;
+
+	node = io_rsrc_node_lookup(&ctx->file_table.data, offset);
+	if (!node)
+		return -EBADF;
+	io_reset_rsrc_node(ctx, &ctx->file_table.data, offset);
+	io_file_bitmap_clear(&ctx->file_table, offset);
+	return 0;
+}
+
+int io_register_file_alloc_range(struct io_ring_ctx *ctx,
+				 struct io_uring_file_index_range __user *arg)
+{
+	struct io_uring_file_index_range range;
+	u32 end;
+
+	if (copy_from_user(&range, arg, sizeof(range)))
+		return -EFAULT;
+	if (check_add_overflow(range.off, range.len, &end))
+		return -EOVERFLOW;
+	if (range.resv || end > ctx->file_table.data.nr)
+		return -EINVAL;
+
+	io_file_table_set_alloc_range(ctx, range.off, range.len);
+	return 0;
+}