On 7/13/24 03:38, Maxim Levitsky wrote:
1. Getting rid of the segment cache. I am not sure how much it helps
these days - this code is very old.
2. Using a read/write lock - IMHO the cleanest solution but might
also affect performance.
A read/write lock would cause a deadlock between the writer and the
sched_out callback, since they run on the same CPU.
I think the root cause of the issue is that clearing the cache should be
done _after_ the writes (and should have a barrier() at the beginning,
if only for cleanliness). So your patch 1 should leave the clearing of
vmx->segment_cache.bitmask where it was.
However, that would still leave an assumption: that it's okay that a
sched_out during vmx_vcpu_reset() (or other functions that write segment
data in the VMCS) accesses stale data, as long as the stale data is not
used after vmx_vcpu_reset() returns. Your patch is a safer approach,
but maybe wrap preempt_disable()/preempt_enable() with
vmx_invalidate_segment_cache_start() {
preempt_disable();
}
vmx_invalidate_segment_cache_end() {
vmx->segment_cache.bitmask = 0;
preempt_enable();
}
Paolo
