Subject: fix huge spte write protection

From: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>

    KVM: MMU: fix conflict access permissions in direct sp

    In no-direct mapping, we mark sp is 'direct' when we mapping the
    guest's larger page, but its access is encoded form upper page-struct
    entire not include the last mapping, it will cause access conflict.

    For example, have this mapping:
            [W]
          / PDE1 -> |---|
      P[W]          |   | LPA
          \ PDE2 -> |---|
            [R]

    P have two children, PDE1 and PDE2, both PDE1 and PDE2 mapping the
    same lage page(LPA). The P's access is WR, PDE1's access is WR,
    PDE2's access is RO(just consider read-write permissions here)

    When guest access PDE1, we will create a direct sp for LPA, the sp's
    access is from P, is W, then we will mark the ptes is W in this sp.

    Then, guest access PDE2, we will find LPA's shadow page, is the same as
    PDE's, and mark the ptes is RO.

    So, if guest access PDE1, the incorrect #PF is occured.

    Fixed by encode the last mapping access into direct shadow page

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -338,6 +338,8 @@ static u64 *FNAME(fetch)(struct kvm_vcpu
 			direct = 1;
 			if (!is_dirty_gpte(gw->ptes[level - delta]))
 				access &= ~ACC_WRITE_MASK;
+			access &= gw->pte_access;
+
 			table_gfn = gpte_to_gfn(gw->ptes[level - delta]);
 			/* advance table_gfn when emulating 1gb pages with 4k */
 			if (delta == 0)