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, 262 insertions, 0 deletions

diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
new file mode 100644
index 000000000..974c46918
--- /dev/null
+++ b/drivers/block/zram/zcomp.c
@@ -0,0 +1,262 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/wait.h>
+#include <linux/sched.h>
+#include <linux/cpuhotplug.h>
+#include <linux/vmalloc.h>
+#include <linux/sysfs.h>
+
+#include "zcomp.h"
+
+#include "backend_lzo.h"
+#include "backend_lzorle.h"
+#include "backend_lz4.h"
+#include "backend_lz4hc.h"
+#include "backend_zstd.h"
+#include "backend_deflate.h"
+#include "backend_842.h"
+
+static const struct zcomp_ops *backends[] = {
+#if IS_ENABLED(CONFIG_ZRAM_BACKEND_LZO)
+	&backend_lzorle,
+	&backend_lzo,
+#endif
+#if IS_ENABLED(CONFIG_ZRAM_BACKEND_LZ4)
+	&backend_lz4,
+#endif
+#if IS_ENABLED(CONFIG_ZRAM_BACKEND_LZ4HC)
+	&backend_lz4hc,
+#endif
+#if IS_ENABLED(CONFIG_ZRAM_BACKEND_ZSTD)
+	&backend_zstd,
+#endif
+#if IS_ENABLED(CONFIG_ZRAM_BACKEND_DEFLATE)
+	&backend_deflate,
+#endif
+#if IS_ENABLED(CONFIG_ZRAM_BACKEND_842)
+	&backend_842,
+#endif
+	NULL
+};
+
+static void zcomp_strm_free(struct zcomp *comp, struct zcomp_strm *zstrm)
+{
+	comp->ops->destroy_ctx(&zstrm->ctx);
+	vfree(zstrm->local_copy);
+	vfree(zstrm->buffer);
+	zstrm->buffer = NULL;
+}
+
+static int zcomp_strm_init(struct zcomp *comp, struct zcomp_strm *zstrm)
+{
+	int ret;
+
+	ret = comp->ops->create_ctx(comp->params, &zstrm->ctx);
+	if (ret)
+		return ret;
+
+	zstrm->local_copy = vzalloc(PAGE_SIZE);
+	/*
+	 * allocate 2 pages. 1 for compressed data, plus 1 extra for the
+	 * case when compressed size is larger than the original one
+	 */
+	zstrm->buffer = vzalloc(2 * PAGE_SIZE);
+	if (!zstrm->buffer || !zstrm->local_copy) {
+		zcomp_strm_free(comp, zstrm);
+		return -ENOMEM;
+	}
+	return 0;
+}
+
+static const struct zcomp_ops *lookup_backend_ops(const char *comp)
+{
+	int i = 0;
+
+	while (backends[i]) {
+		if (sysfs_streq(comp, backends[i]->name))
+			break;
+		i++;
+	}
+	return backends[i];
+}
+
+const char *zcomp_lookup_backend_name(const char *comp)
+{
+	const struct zcomp_ops *backend = lookup_backend_ops(comp);
+
+	if (backend)
+		return backend->name;
+
+	return NULL;
+}
+
+/* show available compressors */
+ssize_t zcomp_available_show(const char *comp, char *buf, ssize_t at)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(backends) - 1; i++) {
+		if (!strcmp(comp, backends[i]->name)) {
+			at += sysfs_emit_at(buf, at, "[%s] ",
+					    backends[i]->name);
+		} else {
+			at += sysfs_emit_at(buf, at, "%s ", backends[i]->name);
+		}
+	}
+
+	at += sysfs_emit_at(buf, at, "\n");
+	return at;
+}
+
+struct zcomp_strm *zcomp_stream_get(struct zcomp *comp)
+{
+	for (;;) {
+		struct zcomp_strm *zstrm = raw_cpu_ptr(comp->stream);
+
+		/*
+		 * Inspired by zswap
+		 *
+		 * stream is returned with ->mutex locked which prevents
+		 * cpu_dead() from releasing this stream under us, however
+		 * there is still a race window between raw_cpu_ptr() and
+		 * mutex_lock(), during which we could have been migrated
+		 * from a CPU that has already destroyed its stream.  If
+		 * so then unlock and re-try on the current CPU.
+		 */
+		mutex_lock(&zstrm->lock);
+		if (likely(zstrm->buffer))
+			return zstrm;
+		mutex_unlock(&zstrm->lock);
+	}
+}
+
+void zcomp_stream_put(struct zcomp_strm *zstrm)
+{
+	mutex_unlock(&zstrm->lock);
+}
+
+int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
+		   const void *src, unsigned int *dst_len)
+{
+	struct zcomp_req req = {
+		.src = src,
+		.dst = zstrm->buffer,
+		.src_len = PAGE_SIZE,
+		.dst_len = 2 * PAGE_SIZE,
+	};
+	int ret;
+
+	might_sleep();
+	ret = comp->ops->compress(comp->params, &zstrm->ctx, &req);
+	if (!ret)
+		*dst_len = req.dst_len;
+	return ret;
+}
+
+int zcomp_decompress(struct zcomp *comp, struct zcomp_strm *zstrm,
+		     const void *src, unsigned int src_len, void *dst)
+{
+	struct zcomp_req req = {
+		.src = src,
+		.dst = dst,
+		.src_len = src_len,
+		.dst_len = PAGE_SIZE,
+	};
+
+	might_sleep();
+	return comp->ops->decompress(comp->params, &zstrm->ctx, &req);
+}
+
+int zcomp_cpu_up_prepare(unsigned int cpu, struct hlist_node *node)
+{
+	struct zcomp *comp = hlist_entry(node, struct zcomp, node);
+	struct zcomp_strm *zstrm = per_cpu_ptr(comp->stream, cpu);
+	int ret;
+
+	ret = zcomp_strm_init(comp, zstrm);
+	if (ret)
+		pr_err("Can't allocate a compression stream\n");
+	return ret;
+}
+
+int zcomp_cpu_dead(unsigned int cpu, struct hlist_node *node)
+{
+	struct zcomp *comp = hlist_entry(node, struct zcomp, node);
+	struct zcomp_strm *zstrm = per_cpu_ptr(comp->stream, cpu);
+
+	mutex_lock(&zstrm->lock);
+	zcomp_strm_free(comp, zstrm);
+	mutex_unlock(&zstrm->lock);
+	return 0;
+}
+
+static int zcomp_init(struct zcomp *comp, struct zcomp_params *params)
+{
+	int ret, cpu;
+
+	comp->stream = alloc_percpu(struct zcomp_strm);
+	if (!comp->stream)
+		return -ENOMEM;
+
+	comp->params = params;
+	ret = comp->ops->setup_params(comp->params);
+	if (ret)
+		goto cleanup;
+
+	for_each_possible_cpu(cpu)
+		mutex_init(&per_cpu_ptr(comp->stream, cpu)->lock);
+
+	ret = cpuhp_state_add_instance(CPUHP_ZCOMP_PREPARE, &comp->node);
+	if (ret < 0)
+		goto cleanup;
+
+	return 0;
+
+cleanup:
+	comp->ops->release_params(comp->params);
+	free_percpu(comp->stream);
+	return ret;
+}
+
+void zcomp_destroy(struct zcomp *comp)
+{
+	cpuhp_state_remove_instance(CPUHP_ZCOMP_PREPARE, &comp->node);
+	comp->ops->release_params(comp->params);
+	free_percpu(comp->stream);
+	kfree(comp);
+}
+
+struct zcomp *zcomp_create(const char *alg, struct zcomp_params *params)
+{
+	struct zcomp *comp;
+	int error;
+
+	/*
+	 * The backends array has a sentinel NULL value, so the minimum
+	 * size is 1. In order to be valid the array, apart from the
+	 * sentinel NULL element, should have at least one compression
+	 * backend selected.
+	 */
+	BUILD_BUG_ON(ARRAY_SIZE(backends) <= 1);
+
+	comp = kzalloc_obj(struct zcomp);
+	if (!comp)
+		return ERR_PTR(-ENOMEM);
+
+	comp->ops = lookup_backend_ops(alg);
+	if (!comp->ops) {
+		kfree(comp);
+		return ERR_PTR(-EINVAL);
+	}
+
+	error = zcomp_init(comp, params);
+	if (error) {
+		kfree(comp);
+		return ERR_PTR(error);
+	}
+	return comp;
+}