From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [RFC PATCH] kvm-unit-tests : Basic architecture of VMX nested
 test case
Date: Wed, 24 Jul 2013 08:48:25 +0200
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Cc: Gleb Natapov <gleb@redhat.com>, kvm <kvm@vger.kernel.org>,
	Jan Kiszka <jan.kiszka@web.de>
To: Arthur Chunqi Li <yzt356@gmail.com>
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Il 24/07/2013 08:46, Arthur Chunqi Li ha scritto:
> On Wed, Jul 24, 2013 at 2:40 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> Il 24/07/2013 08:11, Arthur Chunqi Li ha scritto:
>>>
>>> static int vmx_run()
>>> {
>>>     u32 eax;
>>>     bool ret;
>>>
>>>     vmcs_write(HOST_RSP, get_rsp());
>>>     ret = vmlaunch();
>>
>> The compiler can still change rsp between here...
>>
>>>     while (!ret) {
>>>         asm volatile(
>>>             "vmx_return:\n\t"
>>
>> ... and here.
>>
>> If you want to write it in C, the only thing that can be after
>> vmlaunch/vmresume is "exit()".  Else it has to be asm.
> Actually, you mean we need to write all the codes in asm to avoid
> changing to rsp, right?

Not necessarily all the code.  It is also ok to use setjmp/longjmp with
a small asm trampoline, because this method won't care about the exact
rsp values that are used.  But if you want to do as Gleb said, and put
vmx_return just after vmlaunch, it has to be all asm as in KVM's
arch/x86/kvm/vmx.c.

Paolo