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mana vf: poll for shmem ownership before use #966

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mana vf: poll for shmem ownership before use #966

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81bbfaf
mana vf: wait for possession bit to clear before writing to shared me…
Feb 7, 2025
b312805
cargo fmt
Mar 5, 2025
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44 changes: 44 additions & 0 deletions vm/devices/net/mana_driver/src/gdma_driver.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -175,6 +175,29 @@ impl<T: DeviceBacking> Drop for GdmaDriver<T> {
return;
}

// Wait for ownership of the shared memory.
let max_wait_time =
std::time::Instant::now() + Duration::from_millis(HWC_POLL_TIMEOUT_IN_MS);
loop {
let data = self
.bar0
.mem
.read_u32(self.bar0.map.vf_gdma_sriov_shared_reg_start as usize + 28);
if data == u32::MAX {
tracing::error!("Device no longer present");
return;
}
let header = SmcProtoHdr::from(data);
if !header.owner_is_pf() {
break;
}
if std::time::Instant::now() > max_wait_time {
tracing::error!("MANA request timed out waiting for shared memory possession bit to clear; SMC_MSG_TYPE_DESTROY_HWC");
return;
}
std::hint::spin_loop();
}

let hdr = SmcProtoHdr::new()
.with_msg_type(SmcMessageType::SMC_MSG_TYPE_DESTROY_HWC.0)
.with_msg_version(SMC_MSG_TYPE_DESTROY_HWC_VERSION);
Expand Down Expand Up @@ -288,6 +311,27 @@ impl<T: DeviceBacking> GdmaDriver<T> {

let pages = dma_buffer.pfns();

// Wait for ownership of the shared memory.
let mut backoff = Backoff::new(driver);
let mut ctx =
mesh::CancelContext::new().with_timeout(Duration::from_millis(HWC_POLL_TIMEOUT_IN_MS));
let mut hw_failure = false;
loop {
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This is copy/paste. Can we make it a function?

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Yes, and will do. Each is slightly different as it was copied from the wait in each respective function where the response is waited on (one for establish hwc, one for destroy hwc, slightly different from each other though probably not for good reason). To be complete with making a function, we may want all four waits (establish/destroy before sending request, establish/destroy when waiting for response) to be commonized into a single function.

let header = SmcProtoHdr::from(
bar0_mapping.read_u32(map.vf_gdma_sriov_shared_reg_start as usize + 28),
);
if !header.owner_is_pf() {
break;
}
if hw_failure {
anyhow::bail!("MANA request timed out waiting for shared memory possession bit to clear; SMC_MSG_TYPE_ESTABLISH_HWC");
}
hw_failure = matches!(
ctx.until_cancelled(backoff.back_off()).await,
Err(mesh::CancelReason::DeadlineExceeded)
);
}

// Write the shared memory.
fn low(n: u64) -> [u8; 6] {
let n = n.to_ne_bytes();
Expand Down