From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH 2/4] kvm-unit-tests: VMX: Add test cases for CR0/4 shadowing
Date: Sun, 18 Aug 2013 16:07:47 +0200
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Cc: Jan Kiszka <jan.kiszka@web.de>, kvm <kvm@vger.kernel.org>,
	Gleb Natapov <gleb@redhat.com>
To: Arthur Chunqi Li <yzt356@gmail.com>
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Il 15/08/2013 09:59, Arthur Chunqi Li ha scritto:
>> > volatile u32 stage? And we have barrier() to avoid reordering.
> Reordering here is not a big deal here, though it is actually needed
> here. I occurred the following problem:
> 
> stage = 1;
> do something that causes vmexit;
> stage = 2;
> 
> Then the compiler will optimize "stage = 1" and "stage = 2" to one
> instruction "stage =2", since instructions between them don't use
> "stage". Can volatile solve this problem?

I'm not sure if volatile stores are reordered against non-volatile stores.

Better keep set_stage() but write it as

    barrier();
    stage = s;
    barrier();

Paolo