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example(uffd): handle EAGAIN from UFFDIO_ZEROPAGE #5224

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merged 1 commit into from
May 27, 2025
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example(uffd): handle EAGAIN from UFFDIO_ZEROPAGE #5224

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27 changes: 12 additions & 15 deletions src/firecracker/examples/uffd/uffd_utils.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -144,13 +144,12 @@ impl UffdHandler {
let fault_pfn = fault_page_addr / self.page_size as u64;

if self.removed_pages.contains(&fault_pfn) {
self.zero_out(fault_page_addr);
return true;
} else {
for region in self.mem_regions.iter() {
if region.contains(fault_page_addr) {
return self.populate_from_file(region, fault_page_addr, len);
}
return self.zero_out(fault_page_addr);
}

for region in self.mem_regions.iter() {
if region.contains(fault_page_addr) {
return self.populate_from_file(region, fault_page_addr, len);
}
}

Expand Down Expand Up @@ -190,14 +189,12 @@ impl UffdHandler {
true
}

fn zero_out(&mut self, addr: u64) {
let ret = unsafe {
self.uffd
.zeropage(addr as *mut _, self.page_size, true)
.expect("Uffd zeropage failed")
};
// Make sure the UFFD zeroed out some bytes.
assert!(ret > 0);
fn zero_out(&mut self, addr: u64) -> bool {
match unsafe { self.uffd.zeropage(addr as *mut _, self.page_size, true) } {
Ok(r) if r >= 0 => true,
Err(Error::ZeropageFailed(error)) if error as i32 == libc::EAGAIN => false,
r => panic!("Unexpected zeropage result: {:?}", r),
}
}
}

Expand Down