Re: [Xen-devel] [PATCH 25/34] x86/mm/shadow: make it build with !CONFIG_HVM

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.08.18 at 13:04, <wei.liu2@xxxxxxxxxx> wrote:
> On Tue, Aug 21, 2018 at 02:27:40AM -0600, Jan Beulich wrote:
>> 
>> > --- a/xen/arch/x86/mm/shadow/multi.c
>> > +++ b/xen/arch/x86/mm/shadow/multi.c
>> > @@ -2926,18 +2926,25 @@ static int sh_page_fault(struct vcpu *v,
>> >              }
>> >              else
>> >              {
>> > +#if CONFIG_HVM
>> >                  /* Magic MMIO marker: extract gfn for MMIO address */
>> >                  ASSERT(sh_l1e_is_mmio(sl1e));
>> > +                ASSERT(is_hvm_vcpu(v));
>> >                  gpa = (((paddr_t)(gfn_x(sh_l1e_mmio_get_gfn(sl1e))))
>> >                         << PAGE_SHIFT)
>> >                      | (va & ~PAGE_MASK);
>> > +                perfc_incr(shadow_fault_fast_mmio);
>> > +                SHADOW_PRINTK("fast path mmio %#"PRIpaddr"\n", gpa);
>> > +                sh_reset_early_unshadow(v);
>> > +                trace_shadow_gen(TRC_SHADOW_FAST_MMIO, va);
>> > +                return handle_mmio_with_translation(va, gpa >> PAGE_SHIFT,
>> > +                                                    access)
>> > +                    ? EXCRET_fault_fixed : 0;
>> > +#else
>> > +                /* When HVM is not enabled, there shouldn't be MMIO 
>> > marker */
>> > +                BUG();
>> 
>> At the example of this, while I agree we shouldn't reach here for PV,
>> can this nevertheless be the less impactful domain_crash() please?
>> 
> 
> Do you only want this BUG() to be replaced?
> 
> I think the two in shadonw_*_emulation should stay because you will only
> ever get NULL pointer deref if you allow the code to continue.

Did you perhaps remove too much context? From what's left I can't
judge which others you refer to, or what NULL deref you talk about.
Looking back at the full patch - I think I had already suggested that
the two shadow_*_emulation() should altogether go inside #ifdef
CONFIG_HVM, not just their bodies.

Jan



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