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, 78 insertions, 0 deletions

diff --git a/Documentation/fb/tridentfb.rst b/Documentation/fb/tridentfb.rst
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+=========
+Tridentfb
+=========
+
+Tridentfb is a framebuffer driver for some Trident chip based cards.
+
+The following list of chips is thought to be supported although not all are
+tested:
+
+those from the TGUI series 9440/96XX and with Cyber in their names
+those from the Image series and with Cyber in their names
+those with Blade in their names (Blade3D,CyberBlade...)
+the newer CyberBladeXP family
+
+All families are accelerated. Only PCI/AGP based cards are supported,
+none of the older Tridents.
+The driver supports 8, 16 and 32 bits per pixel depths.
+The TGUI family requires a line length to be power of 2 if acceleration
+is enabled. This means that range of possible resolutions and bpp is
+limited comparing to the range if acceleration is disabled (see list
+of parameters below).
+
+Known bugs:
+
+1. The driver randomly locks up on 3DImage975 chip with acceleration
+   enabled. The same happens in X11 (Xorg).
+2. The ramdac speeds require some more fine tuning. It is possible to
+   switch resolution which the chip does not support at some depths for
+   older chips.
+
+How to use it?
+==============
+
+When booting you can pass the video parameter::
+
+	video=tridentfb
+
+The parameters for tridentfb are concatenated with a ':' as in this example::
+
+	video=tridentfb:800x600-16@75,noaccel
+
+The second level parameters that tridentfb understands are:
+
+========  =====================================================================
+noaccel   turns off acceleration (when it doesn't work for your card)
+
+fp	  use flat panel related stuff
+crt 	  assume monitor is present instead of fp
+
+center 	  for flat panels and resolutions smaller than native size center the
+	  image, otherwise use
+stretch
+
+memsize   integer value in KB, use if your card's memory size is misdetected.
+	  look at the driver output to see what it says when initializing.
+
+memdiff   integer value in KB, should be nonzero if your card reports
+	  more memory than it actually has. For instance mine is 192K less than
+	  detection says in all three BIOS selectable situations 2M, 4M, 8M.
+	  Only use if your video memory is taken from main memory hence of
+	  configurable size. Otherwise use memsize.
+	  If in some modes which barely fit the memory you see garbage
+	  at the bottom this might help by not letting change to that mode
+	  anymore.
+
+nativex   the width in pixels of the flat panel.If you know it (usually 1024
+	  800 or 1280) and it is not what the driver seems to detect use it.
+
+bpp	  bits per pixel (8,16 or 32)
+mode	  a mode name like 800x600-8@75 as described in
+	  Documentation/fb/modedb.rst
+========  =====================================================================
+
+Using insane values for the above parameters will probably result in driver
+misbehaviour so take care(for instance memsize=12345678 or memdiff=23784 or
+nativex=93)
+
+Contact: jani@astechnix.ro