Date: Fri, 21 Nov 2014 17:33:09 -0500
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Steven Rostedt <rostedt@goodmis.org>, Tejun Heo <tj@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Don Zickus <dzickus@redhat.com>, Dave Jones <davej@redhat.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        xen-devel@lists.xenproject.org
Subject: Re: frequent lockups in 3.18rc4
Message-ID: <20141121223309.GC19283@laptop.dumpdata.com>
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On Fri, Nov 21, 2014 at 08:51:43PM +0100, Thomas Gleixner wrote:
> On Fri, 21 Nov 2014, Linus Torvalds wrote:
> > Here's the simplified end result. Again, this is TOTALLY UNTESTED. I
> > compiled it and verified that the code generation looks like what I'd
> > have expected, but that's literally it.
> > 
> >   static noinline int vmalloc_fault(unsigned long address)
> >   {
> >         pgd_t *pgd_dst;
> >         pgdval_t pgd_entry;
> >         unsigned index = pgd_index(address);
> > 
> >         if (index < KERNEL_PGD_BOUNDARY)
> >                 return -1;
> > 
> >         pgd_entry = init_mm.pgd[index].pgd;
> >         if (!pgd_entry)
> >                 return -1;
> > 
> >         pgd_dst = __va(PAGE_MASK & read_cr3());
> >         pgd_dst += index;
> > 
> >         if (pgd_dst->pgd)
> >                 return -1;
> > 
> >         ACCESS_ONCE(pgd_dst->pgd) = pgd_entry;
> 
> This will break paravirt. set_pgd/set_pmd are paravirt functions.
> 
> But I'm fine with breaking it, then you just need to change
> CONFIG_PARAVIRT to 'def_bool n'

That is not very nice.
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