From mboxrd@z Thu Jan  1 00:00:00 1970
From: confucius <henanwxr@hotmail.com>
Subject: Manual differ from source code about Unrestricted Guest
Date: Tue, 7 Jun 2011 08:41:04 -0700 (PDT)
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As italics show:
Some processors allow guest software to run in unpaged protected mode or in
real-address
mode, such guest called =E2=80=9Cunrestricted guest=E2=80=9D.
If CR0.PG =3D 0, each linear address is passed directly to the EPT mechanis=
m
for translation to a physical address.=E2=80=9D
References to Intel=C2=AE 64 and IA-32 Architectures Software Developer=E2=
=80=99s Manual
Volume 3B:System Programming Guide, Part 2  22.8 UNRESTRICTED GUESTS

When we set CR0.PG=3D0 of a guest, I think it doesn=E2=80=99t need construc=
t a page
table for the unpaged guest, but I found it construct an identify_map table
for unpaged guest in the source codes of xen. As follow:=20
Xen-4.0/tools/libxc/xc_hvm_build.c=20
setup_guest()
{
=E2=80=A6=E2=80=A6=E2=80=A6=E2=80=A6=E2=80=A6=E2=80=A6=E2=80=A6
/*
     * Identity-map page table is required for running with CR0.PG=3D0 when
     * using Intel EPT. Create a 32-bit non-PAE page directory of
superpages.
     */
    if ( (ident_pt =3D xc_map_foreign_range(
              xc_handle, dom, PAGE_SIZE, PROT_READ | PROT_WRITE,
              special_pfn(SPECIALPAGE_IDENT_PT))) =3D=3D NULL )
        goto error_out;
    for ( i =3D 0; i < PAGE_SIZE / sizeof(*ident_pt); i++ )
        ident_pt[i] =3D ((i << 22) | _PAGE_PRESENT | _PAGE_RW | _PAGE_USER =
|
                       _PAGE_ACCESSED | _PAGE_DIRTY | _PAGE_PSE);
    munmap(ident_pt, PAGE_SIZE);
=E2=80=A6=E2=80=A6=E2=80=A6=E2=80=A6=E2=80=A6=E2=80=A6=E2=80=A6
}

Why construct such identity map table for unpaged guest?
In my opinion, guset_cr3 doesn=E2=80=99t function when set CR0.PG=3D0, can =
guest_cr3
of this unpaged guest point to identity map table?


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