From fd8e162f25d228e0cfc0c4278f797b61a7f45577 Mon Sep 17 00:00:00 2001
From: David Gibson <david@gibson.dropbear.id.au>
Date: Thu, 24 Feb 2022 12:53:49 +1100
Subject: [PATCH] agent: Verify that we allocated as many hugepages as we need

allocate_hugepages() writes to the kernel sysfs file to allocate hugepages
in the Kata VM.  However, even if the write succeeds, it's not certain that
the kernel will actually be able to allocate as many hugepages as we
requested.

This patch reads back the file after writing it to check if we were able to
allocate all the required hugepages.

fixes #3816

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 src/agent/src/mount.rs | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/src/agent/src/mount.rs b/src/agent/src/mount.rs
index e788e18dff..f4b50af6ec 100644
--- a/src/agent/src/mount.rs
+++ b/src/agent/src/mount.rs
@@ -337,6 +337,23 @@ fn allocate_hugepages(logger: &Logger, options: &[String]) -> Result<()> {
     file.write_all(numpages.as_bytes())
         .context(format!("write nr_hugepages failed: {:?}", &path))?;
 
+    // Even if the write succeeds, the kernel isn't guaranteed to be
+    // able to allocate all the pages we requested.  Verify that it
+    // did.
+    let verify = fs::read_to_string(&path).context(format!("reading {:?}", &path))?;
+    let allocated = verify
+        .trim_end()
+        .parse::<u64>()
+        .map_err(|_| anyhow!("Unexpected text {:?} in {:?}", &verify, &path))?;
+    if allocated != size / pagesize {
+        return Err(anyhow!(
+            "Only allocated {} of {} hugepages of size {}",
+            allocated,
+            numpages,
+            pagesize
+        ));
+    }
+
     Ok(())
 }