Reserve space at the base of the kernel area for IGVM info such as the

initial VMSA

Signed-off-by: Jon Lange <jlange@microsoft.com>

igvm_params/src/lib.rs

@@ -56,7 +56,11 @@ pub struct IgvmParamBlock {
     /// to launch guest firmware once kernel initialization is complete.
     pub launch_fw: u8,
 
-    _reserved: [u8; 7],
+    _reserved: [u8; 3],
+
+    /// The amount of space that must be reserved at the base of the kernel
+    /// memory region (e.g. for VMSA contents).
+    pub kernel_reserved_size: u32,
 
     /// The number of bytes in the kernel memory region.
     pub kernel_size: u32,

src/igvm_params.rs

@@ -61,6 +61,13 @@ impl IgvmParams<'_> {
         Ok(MemoryRegion::<PhysAddr>::new(kernel_base, kernel_size))
     }
 
+    pub fn reserved_kernel_area_size(&self) -> usize {
+        self.igvm_param_block
+            .kernel_reserved_size
+            .try_into()
+            .unwrap()
+    }
+
     pub fn page_state_change_required(&self) -> bool {
         self.igvm_param_page.default_shared_pages != 0
     }

src/stage2.rs

@@ -197,6 +197,9 @@ pub extern "C" fn stage2_main(launch_info: &Stage1LaunchInfo) {
     // IGVM parameters.  Otherwise, it will be the base of the kernel
     // region.
     let mut loaded_kernel_phys_end = kernel_region_phys_start;
+    if let SvsmConfig::IgvmConfig(ref igvm_params) = config {
+        loaded_kernel_phys_end = loaded_kernel_phys_end + igvm_params.reserved_kernel_area_size();
+    }
 
     // Map, validate and populate the SVSM kernel ELF's PT_LOAD segments. The
     // segments' virtual address range might not necessarily be contiguous,

src/svsm_paging.rs

@@ -18,14 +18,35 @@ use crate::sev::ghcb::PageStateChangeOp;
 use crate::sev::{pvalidate, PvalidateOp};
 use crate::types::{PageSize, PAGE_SIZE};
 
+struct IgvmParamInfo<'a> {
+    virt_addr: VirtAddr,
+    igvm_params: Option<IgvmParams<'a>>,
+}
+
 pub fn init_page_table(launch_info: &KernelLaunchInfo, kernel_elf: &elf::Elf64File) {
     let vaddr = mm::alloc::allocate_zeroed_page().expect("Failed to allocate root page-table");
     let mut pgtable = PageTableRef::new(unsafe { &mut *vaddr.as_mut_ptr::<PageTable>() });
+    let igvm_param_info = if launch_info.igvm_params_virt_addr != 0 {
+        let addr = VirtAddr::from(launch_info.igvm_params_virt_addr);
+        IgvmParamInfo {
+            virt_addr: addr,
+            igvm_params: Some(IgvmParams::new(addr)),
+        }
+    } else {
+        IgvmParamInfo {
+            virt_addr: VirtAddr::null(),
+            igvm_params: None,
+        }
+    };
 
     // Install mappings for the kernel's ELF segments each.
     // The memory backing the kernel ELF segments gets allocated back to back
     // from the physical memory region by the Stage2 loader.
     let mut phys = PhysAddr::from(launch_info.kernel_region_phys_start);
+    if let Some(ref igvm_params) = igvm_param_info.igvm_params {
+        phys = phys + igvm_params.reserved_kernel_area_size();
+    }
+
     for segment in kernel_elf.image_load_segment_iter(launch_info.kernel_region_virt_start) {
         let vaddr_start = VirtAddr::from(segment.vaddr_range.vaddr_begin);
         let vaddr_end = VirtAddr::from(segment.vaddr_range.vaddr_end);
@@ -47,14 +68,11 @@ pub fn init_page_table(launch_info: &KernelLaunchInfo, kernel_elf: &elf::Elf64Fi
     }
 
     // Map the IGVM parameters if present.
-    if launch_info.igvm_params_virt_addr != 0 {
-        let igvm_params_virt_addr = VirtAddr::from(launch_info.igvm_params_virt_addr);
-        let igvm_params = IgvmParams::new(igvm_params_virt_addr);
-
+    if let Some(ref igvm_params) = igvm_param_info.igvm_params {
         pgtable
             .map_region(
-                igvm_params_virt_addr,
-                igvm_params_virt_addr + igvm_params.size(),
+                igvm_param_info.virt_addr,
+                igvm_param_info.virt_addr + igvm_params.size(),
                 PhysAddr::from(launch_info.igvm_params_phys_addr),
                 PTEntryFlags::data(),
             )