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, 136 insertions, 0 deletions

diff --git a/Documentation/misc-devices/max6875.rst b/Documentation/misc-devices/max6875.rst
new file mode 100644
index 000000000..ad419ac22
--- /dev/null
+++ b/Documentation/misc-devices/max6875.rst
@@ -0,0 +1,136 @@
+=====================
+Kernel driver max6875
+=====================
+
+Supported chips:
+
+  * Maxim MAX6874, MAX6875
+
+    Prefix: 'max6875'
+
+    Addresses scanned: None (see below)
+
+    Datasheet: http://pdfserv.maxim-ic.com/en/ds/MAX6874-MAX6875.pdf
+
+Author: Ben Gardner <bgardner@wabtec.com>
+
+
+Description
+-----------
+
+The Maxim MAX6875 is an EEPROM-programmable power-supply sequencer/supervisor.
+It provides timed outputs that can be used as a watchdog, if properly wired.
+It also provides 512 bytes of user EEPROM.
+
+At reset, the MAX6875 reads the configuration EEPROM into its configuration
+registers.  The chip then begins to operate according to the values in the
+registers.
+
+The Maxim MAX6874 is a similar, mostly compatible device, with more inputs
+and outputs:
+
+===========  ===     ===    ====
+-            vin     gpi    vout
+===========  ===     ===    ====
+MAX6874        6       4       8
+MAX6875        4       3       5
+===========  ===     ===    ====
+
+See the datasheet for more information.
+
+
+Sysfs entries
+-------------
+
+eeprom        - 512 bytes of user-defined EEPROM space.
+
+
+General Remarks
+---------------
+
+Valid addresses for the MAX6875 are 0x50 and 0x52.
+
+Valid addresses for the MAX6874 are 0x50, 0x52, 0x54 and 0x56.
+
+The driver does not probe any address, so you explicitly instantiate the
+devices.
+
+Example::
+
+  $ modprobe max6875
+  $ echo max6875 0x50 > /sys/bus/i2c/devices/i2c-0/new_device
+
+The MAX6874/MAX6875 ignores address bit 0, so this driver attaches to multiple
+addresses.  For example, for address 0x50, it also reserves 0x51.
+The even-address instance is called 'max6875', the odd one is 'dummy'.
+
+
+Programming the chip using i2c-dev
+----------------------------------
+
+Use the i2c-dev interface to access and program the chips.
+
+Reads and writes are performed differently depending on the address range.
+
+The configuration registers are at addresses 0x00 - 0x45.
+
+Use i2c_smbus_write_byte_data() to write a register and
+i2c_smbus_read_byte_data() to read a register.
+
+The command is the register number.
+
+Examples:
+
+To write a 1 to register 0x45::
+
+  i2c_smbus_write_byte_data(fd, 0x45, 1);
+
+To read register 0x45::
+
+  value = i2c_smbus_read_byte_data(fd, 0x45);
+
+
+The configuration EEPROM is at addresses 0x8000 - 0x8045.
+
+The user EEPROM is at addresses 0x8100 - 0x82ff.
+
+Use i2c_smbus_write_word_data() to write a byte to EEPROM.
+
+The command is the upper byte of the address: 0x80, 0x81, or 0x82.
+The data word is the lower part of the address or'd with data << 8::
+
+  cmd = address >> 8;
+  val = (address & 0xff) | (data << 8);
+
+Example:
+
+To write 0x5a to address 0x8003::
+
+  i2c_smbus_write_word_data(fd, 0x80, 0x5a03);
+
+
+Reading data from the EEPROM is a little more complicated.
+
+Use i2c_smbus_write_byte_data() to set the read address and then
+i2c_smbus_read_byte() or i2c_smbus_read_i2c_block_data() to read the data.
+
+Example:
+
+To read data starting at offset 0x8100, first set the address::
+
+  i2c_smbus_write_byte_data(fd, 0x81, 0x00);
+
+And then read the data::
+
+  value = i2c_smbus_read_byte(fd);
+
+or::
+
+  count = i2c_smbus_read_i2c_block_data(fd, 0x84, 16, buffer);
+
+The block read should read 16 bytes.
+
+0x84 is the block read command.
+
+See the datasheet for more details.
+