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

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

[Vinson Lee]

On Tue, May 26, 2015 at 7:53 PM, Xiao Guangrong
<guangrong.xiao@linux.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@linux-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@linux.intel.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Andrew Morton <akpm@linux-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

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

[Luis Henriques]

On Mon, Jun 08, 2015 at 10:14:49PM -0700, Vinson Lee wrote:
> On Tue, May 26, 2015 at 7:53 PM, Xiao Guangrong
> <guangrong.xiao@linux.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@linux-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@linux.intel.com>
> > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> >
> > Should be found at -mm tree.
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/
> 
> 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
> --
> To unsubscribe from this list: send the line "unsubscribe stable" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

I believe you're referring to the following commit:

commit 5ec45a192fe6e287f0fc06d5ca4f3bd446d94803
Author: Andrew Morton <akpm@linux-foundation.org>
Date:   Wed Jun 10 11:15:02 2015 -0700

    arch/x86/kvm/mmu.c: work around gcc-4.4.4 bug

I am queuing it for the 3.16 kernel.  Thanks!

Cheers,
--
Lu�s