On Mon, Nov 14, 2011, Avi Kivity wrote about "Re: [PATCH 02/10] nEPT: MMU
context for nested EPT":
> > >> +#if PTTYPE == EPT
> > >> + real_gfn = mmu->translate_gpa(vcpu,
> > >> gfn_to_gpa(table_gfn),
> > >> + EPT_WRITABLE_MASK);
> > >> +#else
> > >> real_gfn = mmu->translate_gpa(vcpu,
> > >> gfn_to_gpa(table_gfn),
> > >>
> > >> PFERR_USER_MASK|PFERR_WRITE_MASK);
> > >> +#endif
> > >> +
> > >
> > > Unneeded, I think.
> >
> > Is it because translate_nested_gpa always set USER_MASK ?
>
> Yes... maybe that function needs to do something like
>
> access |= mmu->default_access;
Unless I'm misunderstanding something, translate_nested_gpa, and
gva_to_gpa, take as their "access" parameter a bitmask of PFERR_*,
so it's fine for PFERR_USER_MASK to be enabled in translate_nested_gpa;
It just shouldn't cause PT_USER_MASK to be used. The only additional
problem I can find is in walk_addr_generic which
does
if (!check_write_user_access(vcpu, write_fault, user_fault,
pte))
eperm = true;
and that checks pte & PT_USER_MASK, which it shouldn't if
PTTYPE==PTTYPE_EPT.
It's really confusing that we now have in mmu.c no less than 4 (!)
access bit schemes, similar in many ways but different in many others:
1. page fault error codes (PFERR_*_MASK)
2. x86 page tables acess bits (PT_*_MASK)
3. KVM private access bits (ACC_*_MASK)
4. EPT access bits (VMX_EPT_*_MASK).
I just have to try hard not to confuse them.
--
Nadav Har'El | Thursday, Dec 8 2011,
n...@math.technion.ac.il |-----------------------------------------
Phone +972-523-790466, ICQ 13349191 |Sorry, but my karma just ran over your
http://nadav.harel.org.il |dogma.
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