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, 90 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-bus-siox b/Documentation/ABI/testing/sysfs-bus-siox
new file mode 100644
index 000000000..50e80238f
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-siox
@@ -0,0 +1,90 @@
+What:		/sys/bus/siox/devices/siox-X/active
+KernelVersion:	4.16
+Contact:	Thorsten Scherer <t.scherer@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		On reading represents the current state of the bus. If it
+		contains a "0" the bus is stopped and connected devices are
+		expected to not do anything because their watchdog triggered.
+		When the file contains a "1" the bus is operated and periodically
+		does a push-pull cycle to write and read data from the
+		connected devices.
+
+		When writing a "0" or "1" the bus moves to the described state.
+
+What:		/sys/bus/siox/devices/siox-X/device_add
+KernelVersion:	4.16
+Contact:	Thorsten Scherer <t.scherer@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Write-only file. Write
+
+			<type> <inbytes> <outbytes> <statustype>
+
+		to add a new device dynamically. <type> is the name that is used to match
+		to a driver (similar to the platform bus). <inbytes> and <outbytes> define
+		the length of the input and output shift register in bytes respectively.
+
+		<statustype> defines the 4 bit device type that is check to identify connection
+		problems.
+
+		The new device is added to the end of the existing chain.
+
+What:		/sys/bus/siox/devices/siox-X/device_remove
+KernelVersion:	4.16
+Contact:	Thorsten Scherer <t.scherer@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Write-only file. A single write removes the last device in the siox chain.
+
+What:		/sys/bus/siox/devices/siox-X/poll_interval_ns
+KernelVersion:	4.16
+Contact:	Thorsten Scherer <t.scherer@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Defines the interval between two poll cycles in nano seconds.
+		Note this is rounded to jiffies on writing. On reading the current value
+		is returned.
+
+What:		/sys/bus/siox/devices/siox-X-Y/connected
+KernelVersion:	4.16
+Contact:	Thorsten Scherer <t.scherer@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Read-only value. "0" means the Yth device on siox bus X isn't "connected" i.e.
+		communication with it is not ensured. "1" signals a working connection.
+
+What:		/sys/bus/siox/devices/siox-X-Y/inbytes
+KernelVersion:	4.16
+Contact:	Thorsten Scherer <t.scherer@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Read-only value reporting the inbytes value provided to siox-X/device_add
+
+What:		/sys/bus/siox/devices/siox-X-Y/status_errors
+KernelVersion:	4.16
+Contact:	Thorsten Scherer <t.scherer@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Counts the number of time intervals when the read status byte doesn't yield the
+		expected value.
+
+What:		/sys/bus/siox/devices/siox-X-Y/type
+KernelVersion:	4.16
+Contact:	Thorsten Scherer <t.scherer@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Read-only value reporting the type value provided to siox-X/device_add.
+
+What:		/sys/bus/siox/devices/siox-X-Y/watchdog
+KernelVersion:	4.16
+Contact:	Thorsten Scherer <t.scherer@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Read-only value reporting if the watchdog of the siox device is
+		active. "0" means the watchdog is not active and the device is expected to
+		be operational. "1" means the watchdog keeps the device in reset.
+
+What:		/sys/bus/siox/devices/siox-X-Y/watchdog_errors
+KernelVersion:	4.16
+Contact:	Thorsten Scherer <t.scherer@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Read-only value reporting the number to time intervals when the
+		watchdog was active.
+
+What:		/sys/bus/siox/devices/siox-X-Y/outbytes
+KernelVersion:	4.16
+Contact:	Thorsten Scherer <t.scherer@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Read-only value reporting the outbytes value provided to siox-X/device_add.