commit 02c6f56baf3193658de13ae5bb118a1e78fc7569
author Pierre-Clément Tosi <ptosi@google.com> Fri Dec 06 19:12:24 2024 +0000
committer Pierre-Clément Tosi <ptosi@google.com> Fri Dec 06 19:18:23 2024 +0000
tree 78783bcc2c04f86ac3738655004ac52822b4584a
parent 4edfdadf57137c663e61910a453b5cff3cd87736

vmbase: Add map_data_noflush()

Support use-cases where clients want to map pages R/W and know that they
won't rely on the cache flushing of deactivate_dynamic_page_tables(),
such as pvmfw mapping the kernel payload R/W when booted in EFI mode.

At a low-level, map_data_noflush() doesn't need to create page-level
mappings for accurate dirty state tracking, unlike map_data(), which
reduces the total number of page tables, limiting heap pressure.

Test: m pvmfw_bin
Change-Id: I4e9e7d49e353c5d2f81834054e2a669cc4ce46c8

libs/libvmbase/src/memory.rs

diff --git a/libs/libvmbase/src/memory.rs b/libs/libvmbase/src/memory.rs
index fd4706f..9153706 100644
--- a/libs/libvmbase/src/memory.rs
+++ b/libs/libvmbase/src/memory.rs
@@ -26,9 +26,9 @@
 pub use page_table::PageTable;
 pub use shared::MemoryRange;
 pub use tracker::{
-    deactivate_dynamic_page_tables, init_shared_pool, map_data, map_device, map_image_footer,
-    map_rodata, map_rodata_outside_main_memory, resize_available_memory, unshare_all_memory,
-    unshare_all_mmio_except_uart, unshare_uart,
+    deactivate_dynamic_page_tables, init_shared_pool, map_data, map_data_noflush, map_device,
+    map_image_footer, map_rodata, map_rodata_outside_main_memory, resize_available_memory,
+    unshare_all_memory, unshare_all_mmio_except_uart, unshare_uart,
 };
 pub use util::{
     flush, flushed_zeroize, page_4kb_of, PAGE_SIZE, SIZE_128KB, SIZE_16KB, SIZE_2MB, SIZE_4KB,

libs/libvmbase/src/memory/tracker.rs

diff --git a/libs/libvmbase/src/memory/tracker.rs b/libs/libvmbase/src/memory/tracker.rs
index f15c4db..bbff254 100644
--- a/libs/libvmbase/src/memory/tracker.rs
+++ b/libs/libvmbase/src/memory/tracker.rs
@@ -132,6 +132,18 @@
     Ok(())
 }
 
+/// Map the provided range as normal memory, with R/W permissions.
+///
+/// Unlike `map_data()`, `deactivate_dynamic_page_tables()` will not flush caches for the range.
+///
+/// This fails if the range has already been (partially) mapped.
+pub fn map_data_noflush(addr: usize, size: NonZeroUsize) -> Result<()> {
+    let mut locked_tracker = try_lock_memory_tracker()?;
+    let tracker = locked_tracker.as_mut().ok_or(MemoryTrackerError::Unavailable)?;
+    let _ = tracker.alloc_mut_noflush(addr, size)?;
+    Ok(())
+}
+
 /// Map the region potentially holding data appended to the image, with read-write permissions.
 ///
 /// This fails if the footer has already been mapped.
@@ -294,6 +306,16 @@
         self.add(region)
     }
 
+    fn alloc_range_mut_noflush(&mut self, range: &MemoryRange) -> Result<MemoryRange> {
+        let region = MemoryRegion { range: range.clone(), mem_type: MemoryType::ReadWrite };
+        self.check_allocatable(&region)?;
+        self.page_table.map_data(&get_va_range(range)).map_err(|e| {
+            error!("Error during non-flushed mutable range allocation: {e}");
+            MemoryTrackerError::FailedToMap
+        })?;
+        self.add(region)
+    }
+
     /// Maps the image footer, with read-write permissions.
     fn map_image_footer(&mut self) -> Result<MemoryRange> {
         if self.image_footer_mapped {
@@ -318,6 +340,10 @@
         self.alloc_range_mut(&(base..(base + size.get())))
     }
 
+    fn alloc_mut_noflush(&mut self, base: usize, size: NonZeroUsize) -> Result<MemoryRange> {
+        self.alloc_range_mut_noflush(&(base..(base + size.get())))
+    }
+
     /// Checks that the given range of addresses is within the MMIO region, and then maps it
     /// appropriately.
     fn map_mmio_range(&mut self, range: MemoryRange) -> Result<()> {