refactor: move check for not exceeding memslot limit into struct Vm

This is to prepare for memory regions being registered to a VM
incrementally.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

src/vmm/src/builder.rs

@@ -163,7 +163,6 @@ fn create_vmm_and_vcpus(
     // Set up Kvm Vm and register memory regions.
     // Build custom CPU config if a custom template is provided.
     let mut vm = Vm::new(&kvm)?;
-    kvm.check_memory(&guest_memory)?;
     vm.memory_init(&guest_memory)?;
 
     let resource_allocator = ResourceAllocator::new()?;

src/vmm/src/vstate/kvm.rs

@@ -10,7 +10,6 @@ use serde::{Deserialize, Serialize};
 #[cfg(target_arch = "x86_64")]
 use crate::arch::x86_64::xstate::{XstateError, request_dynamic_xstate_features};
 use crate::cpu_config::templates::KvmCapability;
-use crate::vstate::memory::{GuestMemory, GuestMemoryMmap};
 
 /// Errors associated with the wrappers over KVM ioctls.
 /// Needs `rustfmt::skip` to make multiline comments work
@@ -27,8 +26,6 @@ pub enum KvmError {
     #[cfg(target_arch = "x86_64")]
     /// Failed to get supported cpuid: {0}
     GetSupportedCpuId(kvm_ioctls::Error),
-    /// The number of configured slots is bigger than the maximum reported by KVM
-    NotEnoughMemorySlots,
     #[cfg(target_arch = "x86_64")]
     /// Failed to request permission for dynamic XSTATE features: {0}
     XstateFeatures(XstateError),
@@ -39,8 +36,6 @@ pub enum KvmError {
 pub struct Kvm {
     /// KVM fd.
     pub fd: KvmFd,
-    /// Maximum number of memory slots allowed by KVM.
-    pub max_memslots: usize,
     /// Additional capabilities that were specified in cpu template.
     pub kvm_cap_modifiers: Vec<KvmCapability>,
 
@@ -65,13 +60,10 @@ impl Kvm {
         // Check that all desired capabilities are supported.
         Self::check_capabilities(&kvm_fd, &total_caps).map_err(KvmError::Capabilities)?;
 
-        let max_memslots = kvm_fd.get_nr_memslots();
-
         #[cfg(target_arch = "aarch64")]
         {
             Ok(Self {
                 fd: kvm_fd,
-                max_memslots,
                 kvm_cap_modifiers,
             })
         }
@@ -86,7 +78,6 @@ impl Kvm {
 
             Ok(Kvm {
                 fd: kvm_fd,
-                max_memslots,
                 kvm_cap_modifiers,
                 supported_cpuid,
             })
@@ -99,15 +90,6 @@ impl Kvm {
         crate::arch::x86_64::msr::get_msrs_to_save(&self.fd)
     }
 
-    /// Check guest memory does not have more regions than kvm allows.
-    pub fn check_memory(&self, guest_mem: &GuestMemoryMmap) -> Result<(), KvmError> {
-        if guest_mem.num_regions() > self.max_memslots {
-            Err(KvmError::NotEnoughMemorySlots)
-        } else {
-            Ok(())
-        }
-    }
-
     fn combine_capabilities(kvm_cap_modifiers: &[KvmCapability]) -> Vec<u32> {
         let mut total_caps = Self::DEFAULT_CAPABILITIES.to_vec();
         for modifier in kvm_cap_modifiers.iter() {
@@ -143,6 +125,11 @@ impl Kvm {
             kvm_cap_modifiers: self.kvm_cap_modifiers.clone(),
         }
     }
+
+    /// Returns the maximal number of memslots allowed in a [`Vm`]
+    pub fn max_nr_memslots(&self) -> usize {
+        self.fd.get_nr_memslots()
+    }
 }
 #[cfg(target_arch = "aarch64")]
 /// Optional capabilities.

src/vmm/src/vstate/vm/mod.rs

@@ -27,6 +27,7 @@ use crate::vstate::vcpu::VcpuError;
 #[derive(Debug)]
 struct VmCommon {
     fd: VmFd,
+    max_memslots: usize,
 }
 
 /// Errors associated with the wrappers over KVM ioctls.
@@ -44,6 +45,8 @@ pub enum VmError {
     EventFd(std::io::Error),
     /// Failed to create vcpu: {0}
     CreateVcpu(VcpuError),
+    /// The number of configured slots is bigger than the maximum reported by KVM
+    NotEnoughMemorySlots,
 }
 
 /// Contains Vm functions that are usable across CPU architectures
@@ -85,7 +88,10 @@ impl Vm {
             attempt += 1;
         };
 
-        Ok(VmCommon { fd })
+        Ok(VmCommon {
+            fd,
+            max_memslots: kvm.max_nr_memslots(),
+        })
     }
 
     /// Creates the specified number of [`Vcpu`]s.
@@ -110,6 +116,10 @@ impl Vm {
 
     /// Initializes the guest memory.
     pub fn memory_init(&self, guest_mem: &GuestMemoryMmap) -> Result<(), VmError> {
+        if guest_mem.num_regions() > self.common.max_memslots {
+            return Err(VmError::NotEnoughMemorySlots);
+        }
+
         self.set_kvm_memory_regions(guest_mem)
     }