Apache removes Authorization header

Question

Can there be a case in a cache employing a MESI protocol (has l1 and l2 inclusivity employed) where l2 can send an invalid instruction to an already invalid line in l1.

Solution 1

It turned out the the reason was a buggy client implementation.

Solution 2

From the mod_proxy_http docs:

proxy-chain-auth:

If the proxy requires authentication, it will read and consume the proxy authentication credentials sent by the client. With proxy-chain-auth it will also forward the credentials to the next proxy in the chain. This may be necessary if you have a chain of proxies that share authentication information. Security Warning: Do not set this unless you know you need it, as it forwards sensitive information!

Is this what you are looking for?

Comments

[Isuru H]

Good catch on scenario one, missed it. Just wondering if this is part of maintaining inclusive property.

[Peter Cordes]

@IsuruH: Inclusivity is a one-way property. The larger cache is inclusive of the inner cache, but also holds lines the inner cache doesn't. It has to be tag-inclusive so it always knows what the inner cache has, even if the inner cache has M state and thus outer has I. But the inner cache should be able to drop a line any time it wants. (Normally, e.g. after running clflush or an NT store instruction on x86, I think it would also send invalidates to outer caches, but that takes time and to preserve inclusivity L1D has to drop the line before it sends a request asking L2 to do so.)