From 108e8f9dff2392f05f57e668c2a0ab4557f1d354 Mon Sep 17 00:00:00 2001
From: Wei Liu <liuwe@microsoft.com>
Date: Sat, 22 Feb 2025 01:53:09 +0000
Subject: [PATCH] hypervisor: mshv: handle cross-page access in emulator

Signed-off-by: Wei Liu <liuwe@microsoft.com>
---
 hypervisor/src/mshv/x86_64/emulator.rs | 76 +++++++++++++++++++++-----
 1 file changed, 63 insertions(+), 13 deletions(-)

diff --git a/hypervisor/src/mshv/x86_64/emulator.rs b/hypervisor/src/mshv/x86_64/emulator.rs
index e6b0a83ca..a8f38ba86 100644
--- a/hypervisor/src/mshv/x86_64/emulator.rs
+++ b/hypervisor/src/mshv/x86_64/emulator.rs
@@ -35,12 +35,7 @@ impl MshvEmulatorContext<'_> {
         }
     }
 
-    fn read_memory_flags(
-        &self,
-        gva: u64,
-        data: &mut [u8],
-        flags: u32,
-    ) -> Result<(), PlatformError> {
+    fn r(&self, gva: u64, data: &mut [u8], flags: u32) -> Result<(), PlatformError> {
         let gpa = self.translate(gva, flags)?;
         debug!(
             "mshv emulator: memory read {} bytes from [{:#x} -> {:#x}]",
@@ -59,17 +54,38 @@ impl MshvEmulatorContext<'_> {
 
         Ok(())
     }
-}
 
-/// Platform emulation for Hyper-V
-impl PlatformEmulator for MshvEmulatorContext<'_> {
-    type CpuState = EmulatorCpuState;
+    fn read_memory_flags(
+        &self,
+        gva: u64,
+        data: &mut [u8],
+        flags: u32,
+    ) -> Result<(), PlatformError> {
+        let mut len = data.len() as u64;
 
-    fn read_memory(&self, gva: u64, data: &mut [u8]) -> Result<(), PlatformError> {
-        self.read_memory_flags(gva, data, HV_TRANSLATE_GVA_VALIDATE_READ)
+        // Compare the page number of the first and last byte. If they are different, this is a
+        // cross-page access.
+        let pg1 = gva >> HV_HYP_PAGE_SHIFT;
+        let pg2 = (gva + len - 1) >> HV_HYP_PAGE_SHIFT;
+        let cross_page = pg1 != pg2;
+
+        if cross_page {
+            // We only handle one page cross-page access
+            assert!(pg1 + 1 == pg2);
+            let n = (gva + len) & HV_HYP_PAGE_MASK as u64;
+            len -= n;
+        }
+
+        self.r(gva, &mut data[..len as usize], flags)?;
+
+        if cross_page {
+            self.r(gva + len, &mut data[len as usize..], flags)?;
+        }
+
+        Ok(())
     }
 
-    fn write_memory(&mut self, gva: u64, data: &[u8]) -> Result<(), PlatformError> {
+    fn w(&mut self, gva: u64, data: &[u8]) -> Result<(), PlatformError> {
         let gpa = self.translate(gva, HV_TRANSLATE_GVA_VALIDATE_WRITE)?;
         debug!(
             "mshv emulator: memory write {} bytes at [{:#x} -> {:#x}]",
@@ -88,6 +104,40 @@ impl PlatformEmulator for MshvEmulatorContext<'_> {
 
         Ok(())
     }
+}
+
+/// Platform emulation for Hyper-V
+impl PlatformEmulator for MshvEmulatorContext<'_> {
+    type CpuState = EmulatorCpuState;
+
+    fn read_memory(&self, gva: u64, data: &mut [u8]) -> Result<(), PlatformError> {
+        self.read_memory_flags(gva, data, HV_TRANSLATE_GVA_VALIDATE_READ)
+    }
+
+    fn write_memory(&mut self, gva: u64, data: &[u8]) -> Result<(), PlatformError> {
+        let mut len = data.len() as u64;
+
+        // Compare the page number of the first and last byte. If they are different, this is a
+        // cross-page access.
+        let pg1 = gva >> HV_HYP_PAGE_SHIFT;
+        let pg2 = (gva + len - 1) >> HV_HYP_PAGE_SHIFT;
+        let cross_page = pg1 != pg2;
+
+        if cross_page {
+            // We only handle one page cross-page access
+            assert!(pg1 + 1 == pg2);
+            let n = (gva + len) & HV_HYP_PAGE_MASK as u64;
+            len -= n;
+        }
+
+        self.w(gva, &data[..len as usize])?;
+
+        if cross_page {
+            self.w(gva + len, &data[len as usize..])?;
+        }
+
+        Ok(())
+    }
 
     fn cpu_state(&self, cpu_id: usize) -> Result<Self::CpuState, PlatformError> {
         if cpu_id != self.vcpu.vp_index as usize {