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, 88 insertions, 0 deletions

diff --git a/Documentation/driver-api/hsi.rst b/Documentation/driver-api/hsi.rst
new file mode 100644
index 000000000..01b6bebfb
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+++ b/Documentation/driver-api/hsi.rst
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+High Speed Synchronous Serial Interface (HSI)
+=============================================
+
+Introduction
+---------------
+
+High Speed Synchronous Interface (HSI) is a full duplex, low latency protocol,
+that is optimized for die-level interconnect between an Application Processor
+and a Baseband chipset. It has been specified by the MIPI alliance in 2003 and
+implemented by multiple vendors since then.
+
+The HSI interface supports full duplex communication over multiple channels
+(typically 8) and is capable of reaching speeds up to 200 Mbit/s.
+
+The serial protocol uses two signals, DATA and FLAG as combined data and clock
+signals and an additional READY signal for flow control. An additional WAKE
+signal can be used to wakeup the chips from standby modes. The signals are
+commonly prefixed by AC for signals going from the application die to the
+cellular die and CA for signals going the other way around.
+
+::
+
+    +------------+                                 +---------------+
+    |  Cellular  |                                 |  Application  |
+    |    Die     |                                 |      Die      |
+    |            | - - - - - - CAWAKE - - - - - - >|               |
+    |           T|------------ CADATA ------------>|R              |
+    |           X|------------ CAFLAG ------------>|X              |
+    |            |<----------- ACREADY ------------|               |
+    |            |                                 |               |
+    |            |                                 |               |
+    |            |< - - - - -  ACWAKE - - - - - - -|               |
+    |           R|<----------- ACDATA -------------|T              |
+    |           X|<----------- ACFLAG -------------|X              |
+    |            |------------ CAREADY ----------->|               |
+    |            |                                 |               |
+    |            |                                 |               |
+    +------------+                                 +---------------+
+
+HSI Subsystem in Linux
+-------------------------
+
+In the Linux kernel the hsi subsystem is supposed to be used for HSI devices.
+The hsi subsystem contains drivers for hsi controllers including support for
+multi-port controllers and provides a generic API for using the HSI ports.
+
+It also contains HSI client drivers, which make use of the generic API to
+implement a protocol used on the HSI interface. These client drivers can
+use an arbitrary number of channels.
+
+hsi-char Device
+------------------
+
+Each port automatically registers a generic client driver called hsi_char,
+which provides a character device for userspace representing the HSI port.
+It can be used to communicate via HSI from userspace. Userspace may
+configure the hsi_char device using the following ioctl commands:
+
+HSC_RESET
+ flush the HSI port
+
+HSC_SET_PM
+ enable or disable the client.
+
+HSC_SEND_BREAK
+ send break
+
+HSC_SET_RX
+ set RX configuration
+
+HSC_GET_RX
+ get RX configuration
+
+HSC_SET_TX
+ set TX configuration
+
+HSC_GET_TX
+ get TX configuration
+
+The kernel HSI API
+------------------
+
+.. kernel-doc:: include/linux/hsi/hsi.h
+   :internal:
+
+.. kernel-doc:: drivers/hsi/hsi_core.c
+   :export:
+