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, 144 insertions, 0 deletions

diff --git a/drivers/acpi/acpi_pcc.c b/drivers/acpi/acpi_pcc.c
new file mode 100644
index 000000000..438c67189
--- /dev/null
+++ b/drivers/acpi/acpi_pcc.c
@@ -0,0 +1,144 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Author: Sudeep Holla <sudeep.holla@arm.com>
+ * Copyright 2021 Arm Limited
+ *
+ * The PCC Address Space also referred as PCC Operation Region pertains to the
+ * region of PCC subspace that succeeds the PCC signature. The PCC Operation
+ * Region works in conjunction with the PCC Table(Platform Communications
+ * Channel Table). PCC subspaces that are marked for use as PCC Operation
+ * Regions must not be used as PCC subspaces for the standard ACPI features
+ * such as CPPC, RASF, PDTT and MPST. These standard features must always use
+ * the PCC Table instead.
+ *
+ * This driver sets up the PCC Address Space and installs an handler to enable
+ * handling of PCC OpRegion in the firmware.
+ *
+ */
+#include <linux/kernel.h>
+#include <linux/acpi.h>
+#include <linux/completion.h>
+#include <linux/idr.h>
+#include <linux/io.h>
+
+#include <acpi/pcc.h>
+
+/*
+ * Arbitrary retries in case the remote processor is slow to respond
+ * to PCC commands
+ */
+#define PCC_CMD_WAIT_RETRIES_NUM	500ULL
+
+struct pcc_data {
+	struct pcc_mbox_chan *pcc_chan;
+	struct completion done;
+	struct mbox_client cl;
+	struct acpi_pcc_info ctx;
+};
+
+static struct acpi_pcc_info pcc_ctx;
+
+static void pcc_rx_callback(struct mbox_client *cl, void *m)
+{
+	struct pcc_data *data = container_of(cl, struct pcc_data, cl);
+
+	complete(&data->done);
+}
+
+static acpi_status
+acpi_pcc_address_space_setup(acpi_handle region_handle, u32 function,
+			     void *handler_context,  void **region_context)
+{
+	struct pcc_data *data;
+	struct acpi_pcc_info *ctx = handler_context;
+	struct pcc_mbox_chan *pcc_chan;
+	acpi_status ret;
+
+	data = kzalloc_obj(*data);
+	if (!data)
+		return AE_NO_MEMORY;
+
+	data->cl.rx_callback = pcc_rx_callback;
+	data->cl.knows_txdone = true;
+	data->ctx.length = ctx->length;
+	data->ctx.subspace_id = ctx->subspace_id;
+	data->ctx.internal_buffer = ctx->internal_buffer;
+
+	init_completion(&data->done);
+	data->pcc_chan = pcc_mbox_request_channel(&data->cl, ctx->subspace_id);
+	if (IS_ERR(data->pcc_chan)) {
+		pr_err("Failed to find PCC channel for subspace %d\n",
+		       ctx->subspace_id);
+		ret = AE_NOT_FOUND;
+		goto err_free_data;
+	}
+
+	pcc_chan = data->pcc_chan;
+	if (!pcc_chan->mchan->mbox->txdone_irq) {
+		pr_err("This channel-%d does not support interrupt.\n",
+		       ctx->subspace_id);
+		ret = AE_SUPPORT;
+		goto err_free_channel;
+	}
+
+	*region_context = data;
+	return AE_OK;
+
+err_free_channel:
+	pcc_mbox_free_channel(data->pcc_chan);
+err_free_data:
+	kfree(data);
+
+	return ret;
+}
+
+static acpi_status
+acpi_pcc_address_space_handler(u32 function, acpi_physical_address addr,
+			       u32 bits, acpi_integer *value,
+			       void *handler_context, void *region_context)
+{
+	int ret;
+	struct pcc_data *data = region_context;
+	u64 usecs_lat;
+
+	reinit_completion(&data->done);
+
+	/* Write to Shared Memory */
+	memcpy_toio(data->pcc_chan->shmem, (void *)value, data->ctx.length);
+
+	ret = mbox_send_message(data->pcc_chan->mchan, NULL);
+	if (ret < 0)
+		return AE_ERROR;
+
+	/*
+	 * pcc_chan->latency is just a Nominal value. In reality the remote
+	 * processor could be much slower to reply. So add an arbitrary
+	 * amount of wait on top of Nominal.
+	 */
+	usecs_lat = PCC_CMD_WAIT_RETRIES_NUM * data->pcc_chan->latency;
+	ret = wait_for_completion_timeout(&data->done,
+						usecs_to_jiffies(usecs_lat));
+	if (ret == 0) {
+		pr_err("PCC command executed timeout!\n");
+		return AE_TIME;
+	}
+
+	mbox_chan_txdone(data->pcc_chan->mchan, ret);
+
+	memcpy_fromio(value, data->pcc_chan->shmem, data->ctx.length);
+
+	return AE_OK;
+}
+
+void __init acpi_init_pcc(void)
+{
+	acpi_status status;
+
+	status = acpi_install_address_space_handler(ACPI_ROOT_OBJECT,
+						    ACPI_ADR_SPACE_PLATFORM_COMM,
+						    &acpi_pcc_address_space_handler,
+						    &acpi_pcc_address_space_setup,
+						    &pcc_ctx);
+	if (ACPI_FAILURE(status))
+		pr_alert("OperationRegion handler could not be installed\n");
+}