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, 135 insertions, 0 deletions

diff --git a/drivers/crypto/qce/dma.c b/drivers/crypto/qce/dma.c
new file mode 100644
index 000000000..68cafd474
--- /dev/null
+++ b/drivers/crypto/qce/dma.c
@@ -0,0 +1,135 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2012-2014, The Linux Foundation. All rights reserved.
+ */
+
+#include <linux/device.h>
+#include <linux/dmaengine.h>
+#include <crypto/scatterwalk.h>
+
+#include "dma.h"
+
+static void qce_dma_release(void *data)
+{
+	struct qce_dma_data *dma = data;
+
+	dma_release_channel(dma->txchan);
+	dma_release_channel(dma->rxchan);
+	kfree(dma->result_buf);
+}
+
+int devm_qce_dma_request(struct device *dev, struct qce_dma_data *dma)
+{
+	int ret;
+
+	dma->txchan = dma_request_chan(dev, "tx");
+	if (IS_ERR(dma->txchan))
+		return dev_err_probe(dev, PTR_ERR(dma->txchan),
+				     "Failed to get TX DMA channel\n");
+
+	dma->rxchan = dma_request_chan(dev, "rx");
+	if (IS_ERR(dma->rxchan)) {
+		ret = dev_err_probe(dev, PTR_ERR(dma->rxchan),
+				    "Failed to get RX DMA channel\n");
+		goto error_rx;
+	}
+
+	dma->result_buf = kmalloc(QCE_RESULT_BUF_SZ + QCE_IGNORE_BUF_SZ,
+				  GFP_KERNEL);
+	if (!dma->result_buf) {
+		ret = -ENOMEM;
+		goto error_nomem;
+	}
+
+	dma->ignore_buf = dma->result_buf + QCE_RESULT_BUF_SZ;
+
+	return devm_add_action_or_reset(dev, qce_dma_release, dma);
+
+error_nomem:
+	dma_release_channel(dma->rxchan);
+error_rx:
+	dma_release_channel(dma->txchan);
+	return ret;
+}
+
+struct scatterlist *
+qce_sgtable_add(struct sg_table *sgt, struct scatterlist *new_sgl,
+		unsigned int max_len)
+{
+	struct scatterlist *sg = sgt->sgl, *sg_last = NULL;
+	unsigned int new_len;
+
+	while (sg) {
+		if (!sg_page(sg))
+			break;
+		sg = sg_next(sg);
+	}
+
+	if (!sg)
+		return ERR_PTR(-EINVAL);
+
+	while (new_sgl && sg && max_len) {
+		new_len = new_sgl->length > max_len ? max_len : new_sgl->length;
+		sg_set_page(sg, sg_page(new_sgl), new_len, new_sgl->offset);
+		sg_last = sg;
+		sg = sg_next(sg);
+		new_sgl = sg_next(new_sgl);
+		max_len -= new_len;
+	}
+
+	return sg_last;
+}
+
+static int qce_dma_prep_sg(struct dma_chan *chan, struct scatterlist *sg,
+			   int nents, unsigned long flags,
+			   enum dma_transfer_direction dir,
+			   dma_async_tx_callback cb, void *cb_param)
+{
+	struct dma_async_tx_descriptor *desc;
+	dma_cookie_t cookie;
+
+	if (!sg || !nents)
+		return -EINVAL;
+
+	desc = dmaengine_prep_slave_sg(chan, sg, nents, dir, flags);
+	if (!desc)
+		return -EINVAL;
+
+	desc->callback = cb;
+	desc->callback_param = cb_param;
+	cookie = dmaengine_submit(desc);
+
+	return dma_submit_error(cookie);
+}
+
+int qce_dma_prep_sgs(struct qce_dma_data *dma, struct scatterlist *rx_sg,
+		     int rx_nents, struct scatterlist *tx_sg, int tx_nents,
+		     dma_async_tx_callback cb, void *cb_param)
+{
+	struct dma_chan *rxchan = dma->rxchan;
+	struct dma_chan *txchan = dma->txchan;
+	unsigned long flags = DMA_PREP_INTERRUPT | DMA_CTRL_ACK;
+	int ret;
+
+	ret = qce_dma_prep_sg(rxchan, rx_sg, rx_nents, flags, DMA_MEM_TO_DEV,
+			     NULL, NULL);
+	if (ret)
+		return ret;
+
+	return qce_dma_prep_sg(txchan, tx_sg, tx_nents, flags, DMA_DEV_TO_MEM,
+			       cb, cb_param);
+}
+
+void qce_dma_issue_pending(struct qce_dma_data *dma)
+{
+	dma_async_issue_pending(dma->rxchan);
+	dma_async_issue_pending(dma->txchan);
+}
+
+int qce_dma_terminate_all(struct qce_dma_data *dma)
+{
+	int ret;
+
+	ret = dmaengine_terminate_all(dma->rxchan);
+	return ret ?: dmaengine_terminate_all(dma->txchan);
+}