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, 147 insertions, 0 deletions

diff --git a/Documentation/admin-guide/serial-console.rst b/Documentation/admin-guide/serial-console.rst
new file mode 100644
index 000000000..1609e7479
--- /dev/null
+++ b/Documentation/admin-guide/serial-console.rst
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+.. _serial_console:
+
+Linux Serial Console
+====================
+
+To use a serial port as console you need to compile the support into your
+kernel - by default it is not compiled in. For PC style serial ports
+it's the config option next to menu option:
+
+:menuselection:`Character devices --> Serial drivers --> 8250/16550 and compatible serial support --> Console on 8250/16550 and compatible serial port`
+
+You must compile serial support into the kernel and not as a module.
+
+It is possible to specify multiple devices for console output. You can
+define a new kernel command line option to select which device(s) to
+use for console output.
+
+The format of this option is::
+
+	console=device,options
+
+	device:		tty0 for the foreground virtual console
+			ttyX for any other virtual console
+			ttySx for a serial port
+			lp0 for the first parallel port
+			ttyUSB0 for the first USB serial device
+
+	options:	depend on the driver. For the serial port this
+			defines the baudrate/parity/bits/flow control of
+			the port, in the format BBBBPNF, where BBBB is the
+			speed, P is parity (n/o/e), N is number of bits,
+			and F is flow control ('r' for RTS). Default is
+			9600n8. The maximum baudrate is 115200.
+
+You can specify multiple console= options on the kernel command line.
+
+The behavior is well defined when each device type is mentioned only once.
+In this case, the output will appear on all requested consoles. And
+the last device will be used when you open ``/dev/console``.
+So, for example::
+
+	console=ttyS1,9600 console=tty0
+
+defines that opening ``/dev/console`` will get you the current foreground
+virtual console, and kernel messages will appear on both the VGA
+console and the 2nd serial port (ttyS1 or COM2) at 9600 baud.
+
+The behavior is more complicated when the same device type is defined more
+times. In this case, there are the following two rules:
+
+1. The output will appear only on the first device of each defined type.
+
+2. ``/dev/console`` will be associated with the first registered device.
+   Where the registration order depends on how kernel initializes various
+   subsystems.
+
+   This rule is used also when the last console= parameter is not used
+   for other reasons. For example, because of a typo or because
+   the hardware is not available.
+
+The result might be surprising. For example, the following two command
+lines have the same result::
+
+	console=ttyS1,9600 console=tty0 console=tty1
+	console=tty0 console=ttyS1,9600 console=tty1
+
+The kernel messages are printed only on ``tty0`` and ``ttyS1``. And
+``/dev/console`` gets associated with ``tty0``. It is because kernel
+tries to register graphical consoles before serial ones. It does it
+because of the default behavior when no console device is specified,
+see below.
+
+Note that the last ``console=tty1`` parameter still makes a difference.
+The kernel command line is used also by systemd. It would use the last
+defined ``tty1`` as the login console.
+
+If no console device is specified, the first device found capable of
+acting as a system console will be used. At this time, the system
+first looks for a VGA card and then for a serial port. So if you don't
+have a VGA card in your system the first serial port will automatically
+become the console, unless the kernel is configured with the
+CONFIG_NULL_TTY_DEFAULT_CONSOLE option, then it will default to using the
+ttynull device.
+
+You will need to create a new device to use ``/dev/console``. The official
+``/dev/console`` is now character device 5,1.
+
+(You can also use a network device as a console.  See
+``Documentation/networking/netconsole.rst`` for information on that.)
+
+Here's an example that will use ``/dev/ttyS1`` (COM2) as the console.
+Replace the sample values as needed.
+
+1. Create ``/dev/console`` (real console) and ``/dev/tty0`` (master virtual
+   console)::
+
+     cd /dev
+     rm -f console tty0
+     mknod -m 622 console c 5 1
+     mknod -m 622 tty0 c 4 0
+
+2. LILO can also take input from a serial device. This is a very
+   useful option. To tell LILO to use the serial port:
+   In lilo.conf (global section)::
+
+     serial  = 1,9600n8 (ttyS1, 9600 bd, no parity, 8 bits)
+
+3. Adjust to kernel flags for the new kernel,
+   again in lilo.conf (kernel section)::
+
+     append = "console=ttyS1,9600"
+
+4. Make sure a getty runs on the serial port so that you can login to
+   it once the system is done booting. This is done by adding a line
+   like this to ``/etc/inittab`` (exact syntax depends on your getty)::
+
+     S1:23:respawn:/sbin/getty -L ttyS1 9600 vt100
+
+5. Init and ``/etc/ioctl.save``
+
+   Sysvinit remembers its stty settings in a file in ``/etc``, called
+   ``/etc/ioctl.save``. REMOVE THIS FILE before using the serial
+   console for the first time, because otherwise init will probably
+   set the baudrate to 38400 (baudrate of the virtual console).
+
+6. ``/dev/console`` and X
+   Programs that want to do something with the virtual console usually
+   open ``/dev/console``. If you have created the new ``/dev/console`` device,
+   and your console is NOT the virtual console some programs will fail.
+   Those are programs that want to access the VT interface, and use
+   ``/dev/console instead of /dev/tty0``. Some of those programs are::
+
+     Xfree86, svgalib, gpm, SVGATextMode
+
+   It should be fixed in modern versions of these programs though.
+
+   Note that if you boot without a ``console=`` option (or with
+   ``console=/dev/tty0``), ``/dev/console`` is the same as ``/dev/tty0``.
+   In that case everything will still work.
+
+7. Thanks
+
+   Thanks to Geert Uytterhoeven <geert@linux-m68k.org>
+   for porting the patches from 2.1.4x to 2.1.6x for taking care of
+   the integration of these patches into m68k, ppc and alpha.
+
+Miquel van Smoorenburg <miquels@cistron.nl>, 11-Jun-2000