linux-kernel - Re: [PATCH] KVM: nVMX: Fix IRQs inject to L2 which belong to L1 since race

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Date:	Fri, 04 Jul 2014 13:28:34 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Bandan Das <bsd@...hat.com>
CC:	Gleb Natapov <gleb@...nel.org>, Hu Robert <robert.hu@...el.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: nVMX: Fix IRQs inject to L2 which belong to L1 since
 race

Il 04/07/2014 13:07, Jan Kiszka ha scritto:
> On 2014-07-04 12:52, Jan Kiszka wrote:
>> On 2014-07-04 11:38, Paolo Bonzini wrote:
>>> Il 04/07/2014 11:33, Jan Kiszka ha scritto:
>>>>
>>>> The compiler is not aware of the fact that push/pop exists in this
>>>> function and, thus, places the vmcs parameter on the stack without
>>>> reserving the space. So the pushfq will overwrite the vmcs pointer and
>>>> let the function fail.
>>>
>>> Is that just a missing "memory" clobber?  push/pop clobbers memory.
>>
>> Nope, we would needs some clobber like "stack". I wonder what is
>> required to use push in inline assembly safely?
>
> My colleague just found the answer: -mno-red-zone is required for 64-bit
> in order to play freely with the stack (or you need to stay off that
> zone, apparently some 128 bytes below the stack pointer). The kernel
> sets that switch, our unit tests do not.

Are you posting a patch?  (Also, what compiler is that?)

Paolo

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