I took your suggestion and passed in from
Windows code the PFN (indirectly) to be associated with the MFN found in the
grant table entry referenced.
I modified create_grant_host_mapping()
in mm.c to have an additional IF statement based on a new flag I added:
// RRC: new code.
if ( flags &
GNTMAP_contains_physaddr )
return create_pfn_to_mfn_mapping(addr, frame, current);
The new routine does something similar to
the XENMEM_add_to_physmap code. This code appear to do what I wanted,
which is to replace the mapping from GPFN to MFN. When I run it, it does
appear to change the mapping correctly as you can see from my debug statements:
// RRC: new routine to use with grant
table map ref.
static int create_pfn_to_mfn_mapping(
uint64_t addr, mfn_t
mfn, struct vcpu *v)
{
unsigned long prev_mfn,
gpfn;
struct domain *d =
v->domain;
// This call is only
valid for translated domains.
// The MFN specified
must not be 0.
if (
!shadow_mode_translate(d) || (mfn == 0) )
{
return -EINVAL;
}
// Get the frame
number.
gpfn = (unsigned
long)(addr >> PAGE_SHIFT);
LOCK_BIGLOCK(d);
/* Remove previously
mapped page if it was present. */
prev_mfn =
gmfn_to_mfn(d, gpfn);
// RRC: debug
gdprintk(XENLOG_WARNING, "create_pfn_to_mfn_mapping: pfn:%"PRIx64"
prev MFN:0x%x\n",
(u64)gpfn, (u32)prev_mfn);
if ( mfn_valid(prev_mfn)
)
{
if ( IS_XEN_HEAP_FRAME(mfn_to_page(prev_mfn)) )
{
gdprintk(XENLOG_WARNING, "removing xen heap frame\n");
/* Xen heap frames are simply unhooked from this phys slot. */
guest_physmap_remove_page(d, gpfn, prev_mfn);
}
else
{
gdprintk(XENLOG_WARNING, "removing normal domain frame\n");
/* Normal domain memory is freed, to avoid
leaking memory. */
guest_remove_page(d, gpfn);
}
}
/* Map at new location.
*/
guest_physmap_add_page(d, gpfn, mfn);
UNLOCK_BIGLOCK(d);
return 0;
}
XEN) mm.c:2643:d3 grant host mapping: pa:1697000
frame:0x14f0d4
(XEN) mm.c:2608:d3
create_pfn_to_mfn_mapping: pfn:1697 prev MFN:0x7e5f0
(XEN) mm.c:2621:d3 removing normal domain
frame
(XEN) memory.c:164:d3 guest_remove_page
GMFN:0x1697, MFN:0x7e5f0
(XEN) memory.c:181:d3 guest_remove_page
type_info:0xe8000001, count_info:0x80000004
(XEN) memory.c:192:d3 guest_remove_page
page_is_removable:0x0
(XEN) common.c:2194:d3
sh_remove_all_mappings gmfn:0x7e5f0
(XEN) common.c:3098:d3
sh_p2m_remove_page removing gfn=0x1697 mfn=0x7e5f0
(XEN) common.c:2194:d3
sh_remove_all_mappings gmfn:0x7e5f0
(XEN) common.c:3137:d3
shadow_guest_physmap_add_page: gfn 0x1697, mfn 0x14f0d4
(XEN) common.c:3147:d3
shadow_guest_physmap_add_page: gfn 0x1697, omfn 0xffffffff
(XEN) common.c:3172:d3
shadow_guest_physmap_add_page: sh_mfn_to_gfn ogfn 0x1697, mfn 0x14f0d4
(XEN) common.c:3204:d3
shadow_guest_physmap_add_page: shadow_set_p2m_entry gfn=0x1697 -> mfn
0x14f0d4
(XEN) common.c:3209:d3
shadow_guest_physmap_add_page: set_gpfn_from_mfn gfn=0x1697 -> mfn 0x14f0d4
I then attempt to read the newly re-mapped
page from Windows and I get an error message from get_page_from_l1e() in mm.c
/* Foreign mappings
into guests in shadow external mode don't
* contribute to
writeable mapping refcounts. (This allows the
* qemu-dm helper
process in dom0 to map the domain's memory without
* messing up the
count of "real" writable mappings.) */
okay =
(((l1e_get_flags(l1e) & _PAGE_RW) &&
!(unlikely(shadow_mode_external(d) && (d != current->domain))))
? get_page_and_type(page, d, PGT_writable_page)
: get_page(page, d));
if ( !okay )
{
MEM_LOG("Error getting mfn %lx (pfn %lx) from L1 entry %" PRIpte
" for dom%d",
mfn, get_gpfn_from_mfn(mfn),
l1e_get_intpte(l1e), d->domain_id);
}
It looks like get_page_and_type is returning
0.
(XEN) mm.c:633:d3 l1e_get_flags(l1e)
=0x63, shadow_mode_external(d)= 0x4000,
current->domain=0x3,get_page_and_type=0x0, get_page(page, d)=0x0
(XEN) mm.c:639:d3 Error getting mfn 14f0d4
(pfn 1697) from L1 entry 000000014f0d4063 for dom3
Domain 2 is the grantor and Domain 3 is
the grantee in this example. It appears to me that it is failing because
dom3 is not the owner of the shared page
if ( unlikely((x & PGC_count_mask) == 0) || /* Not allocated? */
unlikely((nx & PGC_count_mask) == 0) || /* Count overflow? */
unlikely(d != _domain)
)
/* Wrong owner? */
Any suggestions?
From: Keir Fraser
[mailto:keir@xxxxxxxxxxxxx]
Sent: Tuesday, July 03, 2007 5:04
AM
To: Roger Cruz;
xen-devel@xxxxxxxxxxxxxxxxxxx
Cc: Tim Deegan
Subject: Re: [Xen-devel] Walking
an HVM's shadow page tables and other memory management questions.
You are barking up the wrong tree
by attempting to poke the mapping into a guest pte. After all, what would you
poke? Guest PTEs address the guest-pseudo-physical space, in which the foreign
page is not present.
You actually want to follow ia64’s lead here. When running in
‘auto-translate’ mode (i.e., on shadow page tables) then the guest
address for a host mapping should not be interpreted as a virtual address but
instead as a pseudo-physical address.
So you will be mapping a grant reference into the pseudo-physical space and
then a guest PTE can map the appropriate pseudo-physical frame number in the
usual way. The slightly tricky bit is working out how to encode a grant-mapping
in the p2m table. My advice would be to use a page-not-present encoding (p2m
table entries are the same format as page-table entries) as this then lets you
define special encodings of your choice with most of the remaining bits.
Tim Deegan may be able to give more advice.
-- Keir
On 2/7/07 21:25, "Roger Cruz" <rcruz@xxxxxxxxxxxxxxxxxxxxxxxx>
wrote:
Hello,
I’m new to Xen and especially to the hypervisor code. I’m
working off a 3.0.4.1 base and have the following questions regarding the
memory management code for an x86, 32-bit platform (capable of supporting PAE).
I’m doing some research into providing grant table hypercall
support from a Windows 2003 HVM. I have made all the necessary changes to
allow the hypercall to make it into the hypervisor and execute the correct
grant table ops.
I’m now testing the GNTTABOP_map_grant_ref with the GNTMAP_host_map and
it correctly obtains the MFN from the grantor domain. It then attempts to
take the HVM host VA address (a windows kernel VA from the non-paged pool) and
walk the guest’s page table to obtain the PFN. I am building the
hypervisor by simply typing “make xen” without any other
configuration changes from a default source installation.
The first problem I encountered is that it appears the code assumes the guest
to be in PAE mode. In particular, guest_walk_tables() in
xen/arch/x86/mm/shadow/multi.c, line 252 has this code snippet:
#else /* PAE only... */
/* Get l3e from the cache of the guest's top level
table */
gw->l3e = (guest_l3e_t
*)&v->arch.shadow.gl3e[guest_l3_table_offset(va)];
#endif /* PAE or 64... */
Which accesses the L3 entries fro the shadow page tables. When I
instrument this code, I get l3e to be 0 as shown below (the line #s won’t
match because of the instrumentation).
(XEN) multi.c:236:d1 guest_walk_tables: va: 0x81699000.
(XEN) multi.c:257:d1 guest_walk_tables: get l3e from cache: 0xff1a6ed0.
(XEN) multi.c:263:d1 guest_walk_tables: l3e not present: 0x0.
(XEN) multi.c:574:d1 sh_guest_map_l1e: va:81699000
If I add the /PAE switch to the boot.ini file, then I can get past this
problem. Hence my statement that it appears the hypervisor is assuming
guests are running with at least PAE mode enable, which may not be the case.
Could someone please guide me here?
The 2nd problem I encountered also has to do with walking the shadow page
tables to obtain the MFN of the underlying Windows VA address.
sh_guest_map_l1e(), Line 520 in the same file, has this code executed after it
walks the guest page tables to obtain the walk_t gw variable.
if ( gw.l2e &&
(guest_l2e_get_flags(*gw.l2e)
& _PAGE_PRESENT) &&
!(guest_supports_superpages(v)
&& (guest_l2e_get_flags(*gw.l2e) & _PAGE_PSE)) )
(XEN) mm.c:2573:d1 grant host mapping: va:81696000 frame:0x15f140
(XEN) mm.c:2507:d1 grant va mapping: va:81696000
(XEN) multi.c:236:d1 guest_walk_tables: va: 0x81696000.
(XEN) multi.c:257:d1 guest_walk_tables: get l3e from cache: 0xff1a6ed0.
(XEN) multi.c:270:d1 guest_walk_tables: l3e flags: 0x1, pfn:0xe9a
(XEN) , mfn:0x9e13d<G><1>multi.c:285:d1 hypervisor l2e mapped
address 0xfec8b058
(XEN) multi.c:315:d1 large pages. 0x1e3
(XEN) multi.c:574:d1 sh_guest_map_l1e: va:81696000
(XEN) multi.c:579:d1 sh_guest_map_l1e: gw.l2e flags:0x1e3, supports large 1
(XEN) multi.c:596:d1 pl1e :0x0,
(XEN) mm.c:2512:d1 Could not find L1 PTE for address 81696000
It looks like it specifically avoids mapping a superpage found in Windows PDE
into the hypervisor’s virtual space, which I assume are 4KB-pages.
What puzzles me is that for a hypercall to read the arguments from the
caller’s guest space, it uses __hvm_copy which calls shadow_gva_to_gfn()
to walk the guest’s shadow page tables to get to the underlying MFN.
Couldn’t this code here also do the same?
Thanks in advance for any insight into this area.
Roger Cruz
Principal SW Engineer
Marathon Technologies Corp.
978-489-1153
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