hypervisor, vmm: Add support for KVM_SEV_SNP_LAUNCH_UPDATE

Implement the KVM_SEV_SNP_LAUNCH_UPDATE ioctl.

Extend Vm::import_isolated_pages() with a uaddrs parameter carrying
host virtual addresses, which KVM needs, unlike MSHV. Compute uaddrs
from guest memory mappings in the IGVM loader.

Add KVM_SEV_SNP_LAUNCH_UPDATE to the seccomp allowlist.

Co-authored-by: Keith Adler <kadler@cloudflare.com>
Signed-off-by: Keith Adler <kadler@cloudflare.com>
Co-authored-by: Alex Orozco <aorozco@google.com>
Signed-off-by: Alex Orozco <aorozco@google.com>
Signed-off-by: Ruben Hakobyan <hruben@meta.com>

hypervisor/src/kvm/mod.rs

@@ -142,6 +142,8 @@ ioctl_io_nr!(KVM_NMI, kvm_bindings::KVMIO, 0x9a);
 
 #[cfg(feature = "sev_snp")]
 use kvm_bindings::{KVM_MEMORY_ATTRIBUTE_PRIVATE, KVM_X86_SNP_VM, kvm_memory_attributes};
+#[cfg(feature = "sev_snp")]
+use x86_64::sev;
 
 #[cfg(feature = "tdx")]
 const KVM_EXIT_TDX: u32 = 50;
@@ -635,6 +637,44 @@ impl vm::Vm for KvmVm {
             .map_err(|e| vm::HypervisorVmError::InitializeSevSnp(e.into()))
     }
 
+    #[cfg(all(feature = "sev_snp", target_arch = "x86_64"))]
+    fn import_isolated_pages(
+        &self,
+        page_type: u32,
+        page_size: u32,
+        // host page frame numbers
+        pfns: &[u64],
+        uaddrs: &[u64],
+    ) -> vm::Result<()> {
+        if pfns.is_empty() {
+            return Ok(());
+        }
+        assert_eq!(pfns.len(), uaddrs.len());
+        // VMSA pages are not supported by launch_update
+        // https://elixir.bootlin.com/linux/v6.11/source/arch/x86/kvm/svm/sev.c#L2377
+        if page_type == sev::SNP_PAGE_TYPE_VMSA {
+            return Ok(());
+        }
+        for i in 0..pfns.len() {
+            self.fd
+                .set_memory_attributes(kvm_memory_attributes {
+                    address: pfns[i] << sev::GPA_METADATA_SHIFT_OFFSET,
+                    size: page_size as u64,
+                    attributes: kvm_bindings::KVM_MEMORY_ATTRIBUTE_PRIVATE as u64,
+                    // Flags must be zero o/w error (flags aren't being used here yet)
+                    flags: 0,
+                })
+                .map_err(|e| vm::HypervisorVmError::ImportIsolatedPages(e.into()))?;
+            self.sev_fd
+                .as_ref()
+                .unwrap()
+                .launch_update(&self.fd, uaddrs[i], page_size as u64, pfns[i], page_type)
+                .map_err(|e| vm::HypervisorVmError::ImportIsolatedPages(e.into()))?;
+        }
+
+        Ok(())
+    }
+
     #[cfg(target_arch = "x86_64")]
     ///
     /// Sets the address of the one-page region in the VM's address space.

hypervisor/src/kvm/x86_64/sev.rs

@@ -19,6 +19,14 @@ pub(crate) type Result<T> = std::result::Result<T, errno::Error>;
 // KVM SEV command IDs — linux/include/uapi/linux/kvm.h
 const KVM_SEV_INIT2: u32 = 22;
 const KVM_SEV_SNP_LAUNCH_START: u32 = 100;
+const KVM_SEV_SNP_LAUNCH_UPDATE: u32 = 101;
+// SNP_LAUNCH_UPDATE page types — linux/arch/x86/include/uapi/asm/sev-guest.h
+pub const SNP_PAGE_TYPE_VMSA: u32 = 2;
+
+// See AMD Spec Section 8.17 — SNP_LAUNCH_UPDATE
+// The last 12 bits are metadata about the guest context
+// https://docs.amd.com/v/u/en-US/56860_PUB_1.58_SEV_SNP
+pub const GPA_METADATA_SHIFT_OFFSET: u32 = 12;
 
 // SNP in VMSA - linux/arch/x86/include/asm/svm.h
 const SVM_SEV_FEAT_SNP_ACTIVE: u64 = 1 << 0;
@@ -59,6 +67,19 @@ pub(crate) struct KvmSevSnpLaunchStart {
     pub pad1: [u64; 4],
 }
 
+#[repr(C, packed)]
+#[derive(Debug, Copy, Clone, Default)]
+pub(crate) struct KvmSevSnpLaunchUpdate {
+    pub gfn_start: u64,
+    pub uaddr: u64,
+    pub len: u64,
+    pub type_: u8,
+    pub pad0: u8,
+    pub flags: u16,
+    pub pad1: u32,
+    pub pad2: [u64; 4],
+}
+
 impl SevFd {
     pub(crate) fn new(sev_path: impl AsRef<Path>) -> Result<Self> {
         let file = OpenOptions::new()
@@ -110,4 +131,30 @@ impl SevFd {
         };
         sev_op(vm, &mut sev_cmd, "KVM_SEV_SNP_LAUNCH_START")
     }
+
+    pub(crate) fn launch_update(
+        &self,
+        vm: &VmFd,
+        // host virtual address
+        hva: u64,
+        size: u64,
+        // guest frame number
+        gfn_start: u64,
+        page_type: u32,
+    ) -> Result<()> {
+        let mut update = KvmSevSnpLaunchUpdate {
+            gfn_start,
+            uaddr: hva,
+            len: size,
+            type_: page_type as u8,
+            ..Default::default()
+        };
+        let mut sev_cmd = kvm_sev_cmd {
+            id: KVM_SEV_SNP_LAUNCH_UPDATE,
+            data: &mut update as *mut KvmSevSnpLaunchUpdate as _,
+            sev_fd: self.fd.as_raw_fd() as _,
+            ..Default::default()
+        };
+        sev_op(vm, &mut sev_cmd, "KVM_SEV_SNP_LAUNCH_UPDATE")
+    }
 }

hypervisor/src/mshv/mod.rs

@@ -2272,6 +2272,7 @@ impl vm::Vm for MshvVm {
         page_type: u32,
         page_size: u32,
         pages: &[u64],
+        _uaddrs: &[u64],
     ) -> vm::Result<()> {
         debug_assert!(page_size == hv_isolated_page_size_HV_ISOLATED_PAGE_SIZE_4KB);
         if pages.is_empty() {

hypervisor/src/vm.rs

@@ -429,6 +429,7 @@ pub trait Vm: Send + Sync + Any {
         _page_type: u32,
         _page_size: u32,
         _pages: &[u64],
+        _uaddrs: &[u64],
     ) -> Result<()> {
         unimplemented!()
     }