From 6dc0189e432add7a5acea9f5615bc8c31461e6e2 Mon Sep 17 00:00:00 2001
From: Ruihan Li <lrh2000@pku.edu.cn>
Date: Tue, 27 May 2025 11:08:47 +0800
Subject: [PATCH] Remove unnecssary overflow checks

---
 ostd/src/mm/dma/dma_coherent.rs | 15 +++++++++------
 ostd/src/mm/dma/dma_stream.rs   | 12 ++++++------
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/ostd/src/mm/dma/dma_coherent.rs b/ostd/src/mm/dma/dma_coherent.rs
index 937bdd24..1ae52bb3 100644
--- a/ostd/src/mm/dma/dma_coherent.rs
+++ b/ostd/src/mm/dma/dma_coherent.rs
@@ -54,13 +54,13 @@ impl DmaCoherent {
     /// The method fails if any part of the given `segment`
     /// already belongs to a DMA mapping.
     pub fn map(segment: USegment, is_cache_coherent: bool) -> core::result::Result<Self, DmaError> {
-        let frame_count = segment.size() / PAGE_SIZE;
         let start_paddr = segment.start_paddr();
+        let frame_count = segment.size() / PAGE_SIZE;
+
         if !check_and_insert_dma_mapping(start_paddr, frame_count) {
             return Err(DmaError::AlreadyMapped);
         }
-        // Ensure that the addresses used later will not overflow
-        start_paddr.checked_add(frame_count * PAGE_SIZE).unwrap();
+
         if !is_cache_coherent {
             let page_table = KERNEL_PAGE_TABLE.get().unwrap();
             let vaddr = paddr_to_vaddr(start_paddr);
@@ -72,6 +72,7 @@ impl DmaCoherent {
                     .unwrap();
             }
         }
+
         let start_daddr = match dma_type() {
             DmaType::Direct => {
                 #[cfg(target_arch = "x86_64")]
@@ -100,6 +101,7 @@ impl DmaCoherent {
                 start_paddr as Daddr
             }
         };
+
         Ok(Self {
             inner: Arc::new(DmaCoherentInner {
                 segment,
@@ -130,10 +132,9 @@ impl Deref for DmaCoherent {
 
 impl Drop for DmaCoherentInner {
     fn drop(&mut self) {
-        let frame_count = self.segment.size() / PAGE_SIZE;
         let start_paddr = self.segment.start_paddr();
-        // Ensure that the addresses used later will not overflow
-        start_paddr.checked_add(frame_count * PAGE_SIZE).unwrap();
+        let frame_count = self.segment.size() / PAGE_SIZE;
+
         match dma_type() {
             DmaType::Direct => {
                 #[cfg(target_arch = "x86_64")]
@@ -157,6 +158,7 @@ impl Drop for DmaCoherentInner {
                 }
             }
         }
+
         if !self.is_cache_coherent {
             let page_table = KERNEL_PAGE_TABLE.get().unwrap();
             let vaddr = paddr_to_vaddr(start_paddr);
@@ -168,6 +170,7 @@ impl Drop for DmaCoherentInner {
                     .unwrap();
             }
         }
+
         remove_dma_mapping(start_paddr, frame_count);
     }
 }
diff --git a/ostd/src/mm/dma/dma_stream.rs b/ostd/src/mm/dma/dma_stream.rs
index e959b680..e0f3035b 100644
--- a/ostd/src/mm/dma/dma_stream.rs
+++ b/ostd/src/mm/dma/dma_stream.rs
@@ -54,13 +54,13 @@ impl DmaStream {
         direction: DmaDirection,
         is_cache_coherent: bool,
     ) -> Result<Self, DmaError> {
-        let frame_count = segment.size() / PAGE_SIZE;
         let start_paddr = segment.start_paddr();
+        let frame_count = segment.size() / PAGE_SIZE;
+
         if !check_and_insert_dma_mapping(start_paddr, frame_count) {
             return Err(DmaError::AlreadyMapped);
         }
-        // Ensure that the addresses used later will not overflow
-        start_paddr.checked_add(frame_count * PAGE_SIZE).unwrap();
+
         let start_daddr = match dma_type() {
             DmaType::Direct => {
                 #[cfg(target_arch = "x86_64")]
@@ -170,10 +170,9 @@ impl HasDaddr for DmaStream {
 
 impl Drop for DmaStreamInner {
     fn drop(&mut self) {
-        let frame_count = self.segment.size() / PAGE_SIZE;
         let start_paddr = self.segment.start_paddr();
-        // Ensure that the addresses used later will not overflow
-        start_paddr.checked_add(frame_count * PAGE_SIZE).unwrap();
+        let frame_count = self.segment.size() / PAGE_SIZE;
+
         match dma_type() {
             DmaType::Direct => {
                 #[cfg(target_arch = "x86_64")]
@@ -198,6 +197,7 @@ impl Drop for DmaStreamInner {
                 }
             }
         }
+
         remove_dma_mapping(start_paddr, frame_count);
     }
 }