Re: [Xen-devel] [PATCH 2/9] x86/np2m: Have invept flush all np2m entries with the same base pointer

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 10/02/2017 10:40 AM, George Dunlap wrote:
> On 10/02/2017 10:37 AM, Sergey Dyasli wrote:
>> On Fri, 2017-09-29 at 16:01 +0100, George Dunlap wrote:
>>> nvmx_handle_invept() updates current's np2m just to flush it.  This is
>>> not only wasteful, but ineffective: if several L2 vcpus share the same
>>> np2m base pointer, they all need to be flushed (not only the current
>>> one).
>>
>> I don't follow this completely. L1 will use INVEPT on each vCPU that
>> shares the same np2m pointer. The main idea here was not to update
>> current's np2m just to flush it.
> 
> Hmm, yes the INVEPT thing is true.  But if that's the case, why do we
> need np2m_flush_base() to loop over the whole list and flush all np2ms
> with the same pointer?

Oh, nevermind -- you don't know which np2m is being used by this vcpu,
so you have to flush all of the np2ms that match that base pointer.

What about this changelog:

---
x86/np2m: Flush p2m rather than switching on nested invept

At the moment, nvmx_handle_invept() updates the current np2m just to
flush it.  Instead introduce a function, np2m_flush_base(), which will
look up the np2m base pointer and call p2m_flush_table() instead.

Unfortunately, since we don't know which p2m a given vcpu is using, we
must flush all p2ms that share that base pointer.

Convert p2m_flush_table() into p2m_flush_table_locked() in order not
to release the p2m_lock after np2m_base check.

Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
---

 -George

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