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, 261 insertions, 0 deletions

diff --git a/drivers/block/rnull/configfs.rs b/drivers/block/rnull/configfs.rs
new file mode 100644
index 000000000..32c10c3f4
--- /dev/null
+++ b/drivers/block/rnull/configfs.rs
@@ -0,0 +1,261 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use super::NullBlkDevice;
+use kernel::{
+    block::mq::gen_disk::{GenDisk, GenDiskBuilder},
+    configfs::{self, AttributeOperations},
+    configfs_attrs,
+    fmt::{self, Write as _},
+    new_mutex,
+    page::PAGE_SIZE,
+    prelude::*,
+    str::{kstrtobool_bytes, CString},
+    sync::Mutex,
+};
+
+pub(crate) fn subsystem() -> impl PinInit<kernel::configfs::Subsystem<Config>, Error> {
+    let item_type = configfs_attrs! {
+        container: configfs::Subsystem<Config>,
+        data: Config,
+        child: DeviceConfig,
+        attributes: [
+            features: 0,
+        ],
+    };
+
+    kernel::configfs::Subsystem::new(c"rnull", item_type, try_pin_init!(Config {}))
+}
+
+#[pin_data]
+pub(crate) struct Config {}
+
+#[vtable]
+impl AttributeOperations<0> for Config {
+    type Data = Config;
+
+    fn show(_this: &Config, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
+        let mut writer = kernel::str::Formatter::new(page);
+        writer.write_str("blocksize,size,rotational,irqmode\n")?;
+        Ok(writer.bytes_written())
+    }
+}
+
+#[vtable]
+impl configfs::GroupOperations for Config {
+    type Child = DeviceConfig;
+
+    fn make_group(
+        &self,
+        name: &CStr,
+    ) -> Result<impl PinInit<configfs::Group<DeviceConfig>, Error>> {
+        let item_type = configfs_attrs! {
+            container: configfs::Group<DeviceConfig>,
+            data: DeviceConfig,
+            attributes: [
+                // Named for compatibility with C null_blk
+                power: 0,
+                blocksize: 1,
+                rotational: 2,
+                size: 3,
+                irqmode: 4,
+            ],
+        };
+
+        Ok(configfs::Group::new(
+            name.try_into()?,
+            item_type,
+            // TODO: cannot coerce new_mutex!() to impl PinInit<_, Error>, so put mutex inside
+            try_pin_init!( DeviceConfig {
+                data <- new_mutex!(DeviceConfigInner {
+                    powered: false,
+                    block_size: 4096,
+                    rotational: false,
+                    disk: None,
+                    capacity_mib: 4096,
+                    irq_mode: IRQMode::None,
+                    name: name.try_into()?,
+                }),
+            }),
+        ))
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub(crate) enum IRQMode {
+    None,
+    Soft,
+}
+
+impl TryFrom<u8> for IRQMode {
+    type Error = kernel::error::Error;
+
+    fn try_from(value: u8) -> Result<Self> {
+        match value {
+            0 => Ok(Self::None),
+            1 => Ok(Self::Soft),
+            _ => Err(EINVAL),
+        }
+    }
+}
+
+impl fmt::Display for IRQMode {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::None => f.write_str("0")?,
+            Self::Soft => f.write_str("1")?,
+        }
+        Ok(())
+    }
+}
+
+#[pin_data]
+pub(crate) struct DeviceConfig {
+    #[pin]
+    data: Mutex<DeviceConfigInner>,
+}
+
+#[pin_data]
+struct DeviceConfigInner {
+    powered: bool,
+    name: CString,
+    block_size: u32,
+    rotational: bool,
+    capacity_mib: u64,
+    irq_mode: IRQMode,
+    disk: Option<GenDisk<NullBlkDevice>>,
+}
+
+#[vtable]
+impl configfs::AttributeOperations<0> for DeviceConfig {
+    type Data = DeviceConfig;
+
+    fn show(this: &DeviceConfig, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
+        let mut writer = kernel::str::Formatter::new(page);
+
+        if this.data.lock().powered {
+            writer.write_str("1\n")?;
+        } else {
+            writer.write_str("0\n")?;
+        }
+
+        Ok(writer.bytes_written())
+    }
+
+    fn store(this: &DeviceConfig, page: &[u8]) -> Result {
+        let power_op = kstrtobool_bytes(page)?;
+        let mut guard = this.data.lock();
+
+        if !guard.powered && power_op {
+            guard.disk = Some(NullBlkDevice::new(
+                &guard.name,
+                guard.block_size,
+                guard.rotational,
+                guard.capacity_mib,
+                guard.irq_mode,
+            )?);
+            guard.powered = true;
+        } else if guard.powered && !power_op {
+            drop(guard.disk.take());
+            guard.powered = false;
+        }
+
+        Ok(())
+    }
+}
+
+#[vtable]
+impl configfs::AttributeOperations<1> for DeviceConfig {
+    type Data = DeviceConfig;
+
+    fn show(this: &DeviceConfig, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
+        let mut writer = kernel::str::Formatter::new(page);
+        writer.write_fmt(fmt!("{}\n", this.data.lock().block_size))?;
+        Ok(writer.bytes_written())
+    }
+
+    fn store(this: &DeviceConfig, page: &[u8]) -> Result {
+        if this.data.lock().powered {
+            return Err(EBUSY);
+        }
+
+        let text = core::str::from_utf8(page)?.trim();
+        let value = text.parse::<u32>().map_err(|_| EINVAL)?;
+
+        GenDiskBuilder::validate_block_size(value)?;
+        this.data.lock().block_size = value;
+        Ok(())
+    }
+}
+
+#[vtable]
+impl configfs::AttributeOperations<2> for DeviceConfig {
+    type Data = DeviceConfig;
+
+    fn show(this: &DeviceConfig, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
+        let mut writer = kernel::str::Formatter::new(page);
+
+        if this.data.lock().rotational {
+            writer.write_str("1\n")?;
+        } else {
+            writer.write_str("0\n")?;
+        }
+
+        Ok(writer.bytes_written())
+    }
+
+    fn store(this: &DeviceConfig, page: &[u8]) -> Result {
+        if this.data.lock().powered {
+            return Err(EBUSY);
+        }
+
+        this.data.lock().rotational = kstrtobool_bytes(page)?;
+
+        Ok(())
+    }
+}
+
+#[vtable]
+impl configfs::AttributeOperations<3> for DeviceConfig {
+    type Data = DeviceConfig;
+
+    fn show(this: &DeviceConfig, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
+        let mut writer = kernel::str::Formatter::new(page);
+        writer.write_fmt(fmt!("{}\n", this.data.lock().capacity_mib))?;
+        Ok(writer.bytes_written())
+    }
+
+    fn store(this: &DeviceConfig, page: &[u8]) -> Result {
+        if this.data.lock().powered {
+            return Err(EBUSY);
+        }
+
+        let text = core::str::from_utf8(page)?.trim();
+        let value = text.parse::<u64>().map_err(|_| EINVAL)?;
+
+        this.data.lock().capacity_mib = value;
+        Ok(())
+    }
+}
+
+#[vtable]
+impl configfs::AttributeOperations<4> for DeviceConfig {
+    type Data = DeviceConfig;
+
+    fn show(this: &DeviceConfig, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
+        let mut writer = kernel::str::Formatter::new(page);
+        writer.write_fmt(fmt!("{}\n", this.data.lock().irq_mode))?;
+        Ok(writer.bytes_written())
+    }
+
+    fn store(this: &DeviceConfig, page: &[u8]) -> Result {
+        if this.data.lock().powered {
+            return Err(EBUSY);
+        }
+
+        let text = core::str::from_utf8(page)?.trim();
+        let value = text.parse::<u8>().map_err(|_| EINVAL)?;
+
+        this.data.lock().irq_mode = IRQMode::try_from(value)?;
+        Ok(())
+    }
+}