vmem: Add stronger tlb invalidation barrier

Signed-off-by: Lucy Menon <168595099+syntactically@users.noreply.github.com>

Author: syntactically

src/hyperlight_guest_bin/src/arch/aarch64/paging.rs

@@ -138,6 +138,8 @@ pub fn phys_to_virt(gpa: vmem::PhysAddr) -> Option<*mut u8> {
 }
 
 pub mod barrier {
+    use hyperlight_common::vmem;
+
     /// # Architecture-specific (aarch64) notes
     ///
     /// I_WZCBG from [1]:
@@ -171,4 +173,16 @@ pub mod barrier {
             );
         }
     }
+
+    #[inline(always)]
+    pub fn downgrade_in_place(var: core::ops::Range<vmem::VirtAddr>) {
+        unsafe {
+            core::arch::asm!("dsb ish");
+            // todo: use TLBI RVAE1IS if FEAT_TLBIRANGE is available
+            for va in var.step_by(vmem::PAGE_SIZE) {
+                core::arch::asm!("tlbi vae1is, {}", in(reg) va >> 12);
+            }
+            core::arch::asm!("dsb ish\nisb");
+        }
+    }
 }

src/hyperlight_guest_bin/src/arch/amd64/paging.rs

@@ -153,6 +153,8 @@ pub fn phys_to_virt(gpa: vmem::PhysAddr) -> Option<*mut u8> {
 
 /// Barriers that other code may need to use when updating page tables
 pub mod barrier {
+    use hyperlight_common::vmem;
+
     /// Call this function when a virtual address has just been made
     /// valid for the first time after the last tlb invalidate that
     /// affected it, and it will be used for the first time in the
@@ -204,4 +206,13 @@ pub mod barrier {
             ", out("rax") _);
         }
     }
+
+    pub fn downgrade_in_place(var: core::ops::Range<vmem::VirtAddr>) {
+        unsafe {
+            // todo: use TLBI RVAE1IS if FEAT_TLBIRANGE is available
+            for va in var.step_by(vmem::PAGE_SIZE) {
+                core::arch::asm!("invlpg [{}]", in(reg) va, options(readonly, nostack, preserves_flags));
+            }
+        }
+    }
 }

src/hyperlight_guest_bin/src/paging.rs

@@ -8,6 +8,12 @@ mod arch;
 pub use arch::{map_region, modify_mapping, phys_to_virt, virt_to_phys};
 /// Barriers that other code may need to use when updating page tables
 pub mod barrier {
+    /// Call this function when a virtual address has had its
+    /// permissions changed in a way that makes previously-valid
+    /// accesses invalid.
+    ///
+    /// Range must be page-aligned.
+    pub use arch::downgrade_in_place;
     /// Call this function when a virtual address has just been made
     /// valid for the first time after the last tlb invalidate that
     /// affected it, and it will be used for the first time in the