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

[Luis Henriques <luis.henriques@canonical.com>]

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.
> >
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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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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,
--
Luís