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

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Date:	Wed, 27 May 2015 10:53:01 +0800
From:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	Edward Cree <ecree@...arflare.com>, Bandan Das <bsd@...hat.com>
CC:	gleb@...nel.org, mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization



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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