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, 101 insertions, 0 deletions

diff --git a/Documentation/admin-guide/cputopology.rst b/Documentation/admin-guide/cputopology.rst
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index 000000000..d29cacc9b
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+++ b/Documentation/admin-guide/cputopology.rst
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+===========================================
+How CPU topology info is exported via sysfs
+===========================================
+
+CPU topology info is exported via sysfs. Items (attributes) are similar
+to /proc/cpuinfo output of some architectures. They reside in
+/sys/devices/system/cpu/cpuX/topology/. Please refer to the ABI file:
+Documentation/ABI/stable/sysfs-devices-system-cpu.
+
+Architecture-neutral, drivers/base/topology.c, exports these attributes.
+However the die, cluster, book, and drawer hierarchy related sysfs files will
+only be created if an architecture provides the related macros as described
+below.
+
+For an architecture to support this feature, it must define some of
+these macros in include/asm-XXX/topology.h::
+
+	#define topology_physical_package_id(cpu)
+	#define topology_die_id(cpu)
+	#define topology_cluster_id(cpu)
+	#define topology_core_id(cpu)
+	#define topology_book_id(cpu)
+	#define topology_drawer_id(cpu)
+	#define topology_sibling_cpumask(cpu)
+	#define topology_core_cpumask(cpu)
+	#define topology_cluster_cpumask(cpu)
+	#define topology_die_cpumask(cpu)
+	#define topology_book_cpumask(cpu)
+	#define topology_drawer_cpumask(cpu)
+
+The type of ``**_id macros`` is int.
+The type of ``**_cpumask macros`` is ``(const) struct cpumask *``. The latter
+correspond with appropriate ``**_siblings`` sysfs attributes (except for
+topology_sibling_cpumask() which corresponds with thread_siblings).
+
+To be consistent on all architectures, include/linux/topology.h
+provides default definitions for any of the above macros that are
+not defined by include/asm-XXX/topology.h:
+
+1) topology_physical_package_id: -1
+2) topology_die_id: -1
+3) topology_cluster_id: -1
+4) topology_core_id: 0
+5) topology_book_id: -1
+6) topology_drawer_id: -1
+7) topology_sibling_cpumask: just the given CPU
+8) topology_core_cpumask: just the given CPU
+9) topology_cluster_cpumask: just the given CPU
+10) topology_die_cpumask: just the given CPU
+11) topology_book_cpumask:  just the given CPU
+12) topology_drawer_cpumask: just the given CPU
+
+Additionally, CPU topology information is provided under
+/sys/devices/system/cpu and includes these files.  The internal
+source for the output is in brackets ("[]").
+
+    =========== ==========================================================
+    kernel_max: the maximum CPU index allowed by the kernel configuration.
+		[NR_CPUS-1]
+
+    offline:	CPUs that are not online because they have been
+		HOTPLUGGED off or exceed the limit of CPUs allowed by the
+		kernel configuration (kernel_max above).
+		[~cpu_online_mask + cpus >= NR_CPUS]
+
+    online:	CPUs that are online and being scheduled [cpu_online_mask]
+
+    possible:	CPUs that have been allocated resources and can be
+		brought online if they are present. [cpu_possible_mask]
+
+    present:	CPUs that have been identified as being present in the
+		system. [cpu_present_mask]
+    =========== ==========================================================
+
+The format for the above output is compatible with cpulist_parse()
+[see <linux/cpumask.h>].  Some examples follow.
+
+In this example, there are 64 CPUs in the system but cpus 32-63 exceed
+the kernel max which is limited to 0..31 by the NR_CPUS config option
+being 32.  Note also that CPUs 2 and 4-31 are not online but could be
+brought online as they are both present and possible::
+
+     kernel_max: 31
+        offline: 2,4-31,32-63
+         online: 0-1,3
+       possible: 0-31
+        present: 0-31
+
+In this example, the NR_CPUS config option is 128, but the kernel was
+started with possible_cpus=144.  There are 4 CPUs in the system and cpu2
+was manually taken offline (and is the only CPU that can be brought
+online.)::
+
+     kernel_max: 127
+        offline: 2,4-127,128-143
+         online: 0-1,3
+       possible: 0-127
+        present: 0-3
+
+See Documentation/core-api/cpu_hotplug.rst for the possible_cpus=NUM
+kernel start parameter as well as more information on the various cpumasks.