linux-kernel - Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization

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Message-ID: <CAHTgTXVjOh_FyqZg6eC9idCTxs5cZavW+-dzkaiOw-Wt6CySuw@mail.gmail.com>
Date:	Mon, 8 Jun 2015 22:14:49 -0700
From:	Vinson Lee <vlee@...pensource.com>
To:	stable@...r.kernel.org
Cc:	Paolo Bonzini <pbonzini@...hat.com>,
	Edward Cree <ecree@...arflare.com>,
	Xiao Guangrong <guangrong.xiao@...ux.intel.com>,
	Bandan Das <bsd@...hat.com>, gleb@...nel.org,
	mtosatti@...hat.com, kvm@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization

On Tue, May 26, 2015 at 7:53 PM, Xiao Guangrong
<guangrong.xiao@...ux.intel.com> wrote:
>
>
> On 05/26/2015 10:48 PM, Paolo Bonzini wrote:
>>
>>
>>
>> On 26/05/2015 16:45, Edward Cree wrote:
>>>>>
>>>>> This breaks older compilers that can't initialize anon structures.
>>>>>
>>>>> How old ? Even gcc 3.1 says you can use unnamed struct/union fields and
>>>>> 3.2 is the minimum version required to compile the kernel as mentioned
>>>>> in the README.
>>>>>
>>>>> We could simply just name the structure, but I doubt this is the
>>>>> only place in the kernel code where it's being used this way :)
>>>
>>> This appears to be GCC bug #10676, see
>>> <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10676>
>>> Says it was fixed in 4.6, but I believe the kernel supports GCCs much
>>> older
>>> than that (back to 3.2).  I personally hit it on 4.4.7, the version
>>> shipped
>>> with RHEL6.6.
>>
>>
>> Yes, it will be fixed soon(ish).  Probably before you can get rid of the
>> obnoxious disclaimer... :)
>
>
> It has been fixed by Andrew:
>
> From: Andrew Morton <akpm@...ux-foundation.org>
> Subject: arch/x86/kvm/mmu.c: work around gcc-4.4.4 bug
>
> arch/x86/kvm/mmu.c: In function 'kvm_mmu_pte_write':
> arch/x86/kvm/mmu.c:4256: error: unknown field 'cr0_wp' specified in
> initializer
> arch/x86/kvm/mmu.c:4257: error: unknown field 'cr4_pae' specified in
> initializer
> arch/x86/kvm/mmu.c:4257: warning: excess elements in union initializer
> ...
>
> gcc-4.4.4 (at least) has issues when using anonymous unions in
> initializers.
>
> Fixes: edc90b7dc4ceef6 ("KVM: MMU: fix SMAP virtualization")
> Cc: Xiao Guangrong <guangrong.xiao@...ux.intel.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
>
> Should be found at -mm tree.
>
> --
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Hi.

Please backport "arch/x86/kvm/mmu.c: work around gcc-4.4.4 bug" to
stable trees that have backported "KVM: MMU: fix SMAP virtualization".

Currently, the Linux 4.0.5 build is broken with GCC 4.4.

"KVM: MMU: fix SMAP virtualization" is currently queued for 3.16.y-ckt
and 3.18.y.

Cheers,
Vinson
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