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Subject: Re: [tip:x86/platform] x86/hyper-v: Use hypercall for remote TLB
 flush
To: Peter Zijlstra <peterz@infradead.org>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
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From: Juergen Gross <jgross@suse.com>
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Date: Fri, 11 Aug 2017 15:07:29 +0200
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On 11/08/17 14:54, Peter Zijlstra wrote:
> On Fri, Aug 11, 2017 at 02:46:41PM +0200, Juergen Gross wrote:
>> Aah, okay. Now I understand the problem. The TLB isn't the issue but the
>> IPI is serving two purposes here: TLB flushing (which is allowed to
>> happen at any time) and serialization regarding access to critical pages
>> (which seems to be broken in the Xen case as you suggest).
> 
> Indeed, and now hyper-v as well.

Is it possible to distinguish between non-critical calls of
flush_tlb_others() (which should be the majority IMHO) and critical ones
regarding above problem? I guess the only problem is the case when a
page table can be freed because its last valid entry is gone, right?

We might want to add a serialization flag to indicate flushing _and_
serialization via IPI should be performed.


Juergen