Hi All,
I'm studing the memory management of Xen, I noticed the Domain0 kernel(Linux) declared
its features in the .section
__xen_guest, just like this:
/*linux-2.6-xen-sparse/arch/i386/kernel/head-xen.S*/
.ascii
",FEATURES=writable_page_tables"
.ascii
"|writable_descriptor_tables"
.ascii
"|auto_translated_physmap"
.ascii
"|pae_pgdir_above_4gb"
.ascii
"|supervisor_mode_kernel"
All these features information
will be parsed by xen before the domain0 kernel image was loaded, and I noticed
when the hypervisor responded to the HYPERVISOR_xen_version(XENVER_get_features, &fi) hypercall of domain0, it will check the PG_translate and PG_SH_enable flags of d->arch.paging.mode of the calling
domain to determine how to fill the output parameter fi, just like this:
/*xen/common/kernel.c*/
if ( shadow_mode_translate(current->domain)
)
fi.submap |=
(1U << XENFEAT_writable_page_tables) |
(1U << XENFEAT_auto_translated_physmap);
and domain0 kernel will use this information to determine how to set its own
feature flags, and whether to do the p2m and m2p translation between pfn and
mfn, the following is an example:
/*linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/maddr.h
*/
static inline
unsigned long pfn_to_mfn(unsigned long pfn)
{
if
(xen_feature(XENFEAT_auto_translated_physmap))
return
pfn;
BUG_ON(max_mapnr
&& pfn >= max_mapnr);
return
phys_to_machine_mapping[pfn] & ~FOREIGN_FRAME_BIT;
}
What I want to know
is whether there are some relationship between the auto_translated_physmap
feature and the shadow_mode_translate
mode of domain, do they have the same meaning? I think this feature will
work(Guest kernel do the p2m and m2p translation) only when the shadow mode of
domain is enabled, but this is not true for domain0 because it's a
paravirtualized domain, why did it still declare this feature? I am looking
forward to your response, thank you very much.
Regards,
HUYanyan
