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, 142 insertions, 0 deletions

diff --git a/samples/rust/rust_dma.rs b/samples/rust/rust_dma.rs
new file mode 100644
index 000000000..bd60034de
--- /dev/null
+++ b/samples/rust/rust_dma.rs
@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust DMA api test (based on QEMU's `pci-testdev`).
+//!
+//! To make this driver probe, QEMU must be run with `-device pci-testdev`.
+
+use kernel::{
+    device::Core,
+    dma::{
+        Coherent,
+        DataDirection,
+        Device,
+        DmaMask, //
+    },
+    io::{
+        io_project,
+        io_read,
+        Io, //
+    },
+    page,
+    pci,
+    prelude::*,
+    scatterlist::{
+        Owned,
+        SGTable, //
+    },
+    sync::aref::ARef, //
+};
+
+#[pin_data(PinnedDrop)]
+struct DmaSampleDriver {
+    pdev: ARef<pci::Device>,
+    ca: Coherent<[MyStruct]>,
+    #[pin]
+    sgt: SGTable<Owned<VVec<u8>>>,
+}
+
+const TEST_VALUES: [(u32, u32); 5] = [
+    (0xa, 0xb),
+    (0xc, 0xd),
+    (0xe, 0xf),
+    (0xab, 0xba),
+    (0xcd, 0xef),
+];
+
+#[derive(FromBytes, IntoBytes)]
+struct MyStruct {
+    h: u32,
+    b: u32,
+}
+
+impl MyStruct {
+    fn new(h: u32, b: u32) -> Self {
+        Self { h, b }
+    }
+}
+// SAFETY: All bit patterns are acceptable values for `MyStruct`.
+unsafe impl kernel::transmute::AsBytes for MyStruct {}
+// SAFETY: Instances of `MyStruct` have no uninitialized portions.
+unsafe impl kernel::transmute::FromBytes for MyStruct {}
+
+kernel::pci_device_table!(
+    PCI_TABLE,
+    <DmaSampleDriver as pci::Driver>::IdInfo,
+    [(pci::DeviceId::from_id(pci::Vendor::REDHAT, 0x5), ())]
+);
+
+impl pci::Driver for DmaSampleDriver {
+    type IdInfo = ();
+    type Data<'bound> = Self;
+    const ID_TABLE: pci::IdTable<Self::IdInfo> = &PCI_TABLE;
+
+    fn probe<'bound>(
+        pdev: &'bound pci::Device<Core<'_>>,
+        _info: Option<&'bound Self::IdInfo>,
+    ) -> impl PinInit<Self, Error> + 'bound {
+        pin_init::pin_init_scope(move || {
+            dev_info!(pdev, "Probe DMA test driver.\n");
+
+            let mask = DmaMask::new::<64>();
+
+            // SAFETY: There are no concurrent calls to DMA allocation and mapping primitives.
+            unsafe { pdev.dma_set_mask_and_coherent(mask)? };
+
+            let ca: Coherent<[MyStruct]> =
+                Coherent::zeroed_slice(pdev.as_ref(), TEST_VALUES.len(), GFP_KERNEL)?;
+
+            for (i, value) in TEST_VALUES.into_iter().enumerate() {
+                io_project!(ca, [panic: i]).copy_write(MyStruct::new(value.0, value.1));
+            }
+
+            let size = 4 * page::PAGE_SIZE;
+            let pages = VVec::with_capacity(size, GFP_KERNEL)?;
+
+            let sgt = SGTable::new(pdev.as_ref(), pages, DataDirection::ToDevice, GFP_KERNEL);
+
+            Ok(try_pin_init!(Self {
+                pdev: pdev.into(),
+                ca,
+                sgt <- sgt,
+            }))
+        })
+    }
+}
+
+impl DmaSampleDriver {
+    fn check_dma(&self) {
+        for (i, value) in TEST_VALUES.into_iter().enumerate() {
+            let val0 = io_read!(self.ca, [panic: i].h);
+            let val1 = io_read!(self.ca, [panic: i].b);
+
+            assert_eq!(val0, value.0);
+            assert_eq!(val1, value.1);
+        }
+    }
+}
+
+#[pinned_drop]
+impl PinnedDrop for DmaSampleDriver {
+    fn drop(self: Pin<&mut Self>) {
+        dev_info!(self.pdev, "Unload DMA test driver.\n");
+
+        self.check_dma();
+
+        for (i, entry) in self.sgt.iter().enumerate() {
+            dev_info!(
+                self.pdev,
+                "Entry[{}]: DMA address: {:#x}",
+                i,
+                entry.dma_address(),
+            );
+        }
+    }
+}
+
+kernel::module_pci_driver! {
+    type: DmaSampleDriver,
+    name: "rust_dma",
+    authors: ["Abdiel Janulgue"],
+    description: "Rust DMA test",
+    license: "GPL v2",
+}