* How to share a page between dom0 and Hypervisror
@ 2011-06-06 13:28 veerasena reddy
2011-06-06 13:53 ` Ian Campbell
0 siblings, 1 reply; 3+ messages in thread
From: veerasena reddy @ 2011-06-06 13:28 UTC (permalink / raw)
To: xen-devel
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Hi,
In one of experiments, I need to map a page allocated in dom0 to hypervisor
and access/modify the page contents in hypervisor.
I tried this by adding a new hypercall, and pass the GPA of the page to its
handler in hypervisor which does the following:
==================== Hypercall handler ================
DO(my_rd_wr)(int cmd, XEN_GUEST_HANDLE(void) arg)
{
unsigned long dom0_gpa;
unsigned long gmfn;
unsigned long mfn;
void *my_rd_wr_page;
struct domain *d = current->domain;
printk(XENLOG_G_DEBUG "%s:L%u: Entered\n", __FUNCTION__, __LINE__);
switch( cmd )
{
case 0x1:
if ( copy_from_guest(&dom0_gpa, arg, 1) )
return -EFAULT;
printk(XENLOG_G_DEBUG "%s:L%u: GPA read 0x%lx\n",
__FUNCTION__, __LINE__,
dom0_gpa);
gmfn = dom0_gpa >> 12;
mfn = gmfn_to_mfn(d, gmfn);
if ( !mfn_valid(mfn) ||
!get_page_and_type(mfn_to_page(mfn), d,
PGT_writable_page) )
{
printk(XENLOG_G_WARNING
"Bad GMFN %lx (MFN %lx)\n", gmfn,
mfn);
return 0;
}
my_rd_wr_page = map_domain_page(mfn);
/* Do your initialization of the page here; just
write '2' in all bytes */
memset(my_rd_wr_page, 2, 1<<12);
unmap_domain_page(my_rd_wr_page);
put_page_and_type(mfn_to_page(mfn));
break;
default:
printk(XENLOG_G_DEBUG "%s:L%u: unhandled\n",
__FUNCTION__, __LINE__);
break;
}
return 0;
}
============================
I have allocated a page from a sample dom0 kernel module (using vmalloc()),
and passed the physical address of it to hypercall.
void my_rd_wr_page_setup(void)
{
unsigned long my_gpa;
int err;
char *my_rd_wr_page = NULL;
my_rd_wr_page = __vmalloc(
1 * PAGE_SIZE,
GFP_KERNEL | __GFP_HIGHMEM,
__pgprot(__PAGE_KERNEL & ~_PAGE_NX));
my_gpa = vmalloc_to_pfn((char *)&my_rd_wr_page) << PAGE_SHIFT;
printk("%s: Before Hypercall; my_rd_wr_page=%p my_gpa=%lx\n",
__FUNCTION__, my_rd_wr_page, my_gpa);
memset(my_rd_wr_page, 0, PAGE_SIZE);
err = _hypercall2(int, my_rd_wr, 0x1, (void *)&my_gpa);
printk("%s: Hypercall returned; errno-%d\n", __FUNCTION__, err);
}
When I loaded the module, the following error has been observed:
=============== On dom0 ===========
xen_features[0].writable_page_tables = 0
xen_features[0].writable_descriptor_tables = 0
xen_features[0].auto_translated_physmap = 0
xen_features[0].supervisor_mode_kernel = 0
xen_features[0].pae_pgdir_above_4gb = 1
my_rd_wr_page_setup: Before Hypercall; my_rd_wr_page=ffffc90010f7e000
my_gpa=d7cf000
my_rd_wr_page_setup: Hypercall returned; errno-0
=====================================
On hypervisor:
(XEN) do_my_rd_wr:L178: GPA read 0xd7cf000
(XEN) mm.c:2037:d0 Error pfn d7cf: rd=ffff8300773c0000, od=0000000000000000,
caf=180000000000000, taf=0000000000000000
(XEN) Bad GMFN d7cf (MFN d7cf)
====================================
>From the dom0 messages (where i read the features), it looks like
writable_page_tables is not set. Is it causing the issue in my case.
Could you please advice if i did something wrong here.
You are most welcome if you have completely different approach which works;
Thanks a lot in advance
Regards,
VSR.
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^ permalink raw reply [flat|nested] 3+ messages in thread* Re: How to share a page between dom0 and Hypervisror
2011-06-06 13:28 How to share a page between dom0 and Hypervisror veerasena reddy
@ 2011-06-06 13:53 ` Ian Campbell
2011-06-06 14:18 ` veerasena reddy
0 siblings, 1 reply; 3+ messages in thread
From: Ian Campbell @ 2011-06-06 13:53 UTC (permalink / raw)
To: veerasena reddy; +Cc: xen-devel@lists.xensource.com
On Mon, 2011-06-06 at 14:28 +0100, veerasena reddy wrote:
> Hi,
>
> In one of experiments, I need to map a page allocated in dom0 to
> hypervisor and access/modify the page contents in hypervisor.
> I tried this by adding a new hypercall, and pass the GPA of the page
> to its handler in hypervisor which does the following:
>
> ==================== Hypercall handler ================
> DO(my_rd_wr)(int cmd, XEN_GUEST_HANDLE(void) arg)
> {
> unsigned long dom0_gpa;
> unsigned long gmfn;
> unsigned long mfn;
> void *my_rd_wr_page;
> struct domain *d = current->domain;
>
> printk(XENLOG_G_DEBUG "%s:L%u: Entered\n", __FUNCTION__, __LINE__);
> switch( cmd )
> {
> case 0x1:
> if ( copy_from_guest(&dom0_gpa, arg, 1) )
> return -EFAULT;
> printk(XENLOG_G_DEBUG "%s:L%u: GPA read 0x%lx\n",
> __FUNCTION__, __LINE__, dom0_gpa);
>
> gmfn = dom0_gpa >> 12;
> mfn = gmfn_to_mfn(d, gmfn);
> if ( !mfn_valid(mfn) ||
> !get_page_and_type(mfn_to_page(mfn), d, PGT_writable_page) )
> {
> printk(XENLOG_G_WARNING
> "Bad GMFN %lx (MFN %lx)\n", gmfn, mfn);
> return 0;
> }
>
> my_rd_wr_page = map_domain_page(mfn);
>
> /* Do your initialization of the page here; just write '2' in all bytes */
> memset(my_rd_wr_page, 2, 1<<12);
>
> unmap_domain_page(my_rd_wr_page);
> put_page_and_type(mfn_to_page(mfn));
> break;
>
> default:
> printk(XENLOG_G_DEBUG "%s:L%u: unhandled\n",
> __FUNCTION__, __LINE__);
> break;
> }
>
> return 0;
> }
> ============================
>
> I have allocated a page from a sample dom0 kernel module (using vmalloc()), and passed the physical address of it to hypercall.
>
> void my_rd_wr_page_setup(void)
> {
> unsigned long my_gpa;
> int err;
> char *my_rd_wr_page = NULL;
>
> my_rd_wr_page = __vmalloc(
> 1 * PAGE_SIZE,
> GFP_KERNEL | __GFP_HIGHMEM,
> __pgprot(__PAGE_KERNEL & ~_PAGE_NX));
>
> my_gpa = vmalloc_to_pfn((char *)&my_rd_wr_page) << PAGE_SHIFT;
&my_rd_wr_page is the address of the variable (i.e. probably a pointer
into the current stack) and not the address of the page you are trying
to reference.
Secondly vmalloc_to_pfn will return you a guest physical address, while
hypercalls from PV guests always take an MFN.
On the hypercall side your call to gmfn_to_mfn is normally an identity
function for a PV guest which map_domain_page takes a machine address.
So I think you need to launder the address through the p2m in the kernel
before passing it to the hypercall.
> printk("%s: Before Hypercall; my_rd_wr_page=%p my_gpa=%lx\n", __FUNCTION__, my_rd_wr_page, my_gpa);
> memset(my_rd_wr_page, 0, PAGE_SIZE);
> err = _hypercall2(int, my_rd_wr, 0x1, (void *)&my_gpa);
> printk("%s: Hypercall returned; errno-%d\n", __FUNCTION__, err);
> }
>
>
> When I loaded the module, the following error has been observed:
>
> =============== On dom0 ===========
> xen_features[0].writable_page_tables = 0
> xen_features[0].writable_descriptor_tables = 0
> xen_features[0].auto_translated_physmap = 0
> xen_features[0].supervisor_mode_kernel = 0
> xen_features[0].pae_pgdir_above_4gb = 1
> my_rd_wr_page_setup: Before Hypercall; my_rd_wr_page=ffffc90010f7e000 my_gpa=d7cf000
> my_rd_wr_page_setup: Hypercall returned; errno-0
> =====================================
> On hypervisor:
> (XEN) do_my_rd_wr:L178: GPA read 0xd7cf000
> (XEN) mm.c:2037:d0 Error pfn d7cf: rd=ffff8300773c0000, od=0000000000000000, caf=180000000000000, taf=0000000000000000
> (XEN) Bad GMFN d7cf (MFN d7cf)
> ====================================
>
> From the dom0 messages (where i read the features), it looks like writable_page_tables is not set. Is it causing the issue in my case.
Writable page tables is something else, it relates to how a _guest_ can
update it's own page tables, not how Xen creates mappings of things.
>
> Could you please advice if i did something wrong here.
> You are most welcome if you have completely different approach which works;
>
> Thanks a lot in advance
>
> Regards,
> VSR.
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: How to share a page between dom0 and Hypervisror
2011-06-06 13:53 ` Ian Campbell
@ 2011-06-06 14:18 ` veerasena reddy
0 siblings, 0 replies; 3+ messages in thread
From: veerasena reddy @ 2011-06-06 14:18 UTC (permalink / raw)
To: Ian Campbell; +Cc: xen-devel@lists.xensource.com
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Hi Ian,
Thanks a lot for the detailed explanation.
You were correct, I had to use "my_rd_wr_page" not "&my_rd_wr_page". I also
had to change my code to translate the PFN to MFN (pfn_to_mfn()) on dom0
kernel itself before passing it to hypercall.
Now it works.
Thanks & Regards,
VSR.
On Mon, Jun 6, 2011 at 7:23 PM, Ian Campbell <Ian.Campbell@citrix.com>wrote:
> On Mon, 2011-06-06 at 14:28 +0100, veerasena reddy wrote:
> > Hi,
> >
> > In one of experiments, I need to map a page allocated in dom0 to
> > hypervisor and access/modify the page contents in hypervisor.
> > I tried this by adding a new hypercall, and pass the GPA of the page
> > to its handler in hypervisor which does the following:
> >
> > ==================== Hypercall handler ================
> > DO(my_rd_wr)(int cmd, XEN_GUEST_HANDLE(void) arg)
> > {
> > unsigned long dom0_gpa;
> > unsigned long gmfn;
> > unsigned long mfn;
> > void *my_rd_wr_page;
> > struct domain *d = current->domain;
> >
> > printk(XENLOG_G_DEBUG "%s:L%u: Entered\n", __FUNCTION__,
> __LINE__);
> > switch( cmd )
> > {
> > case 0x1:
> > if ( copy_from_guest(&dom0_gpa, arg, 1) )
> > return -EFAULT;
> > printk(XENLOG_G_DEBUG "%s:L%u: GPA read 0x%lx\n",
> > __FUNCTION__, __LINE__,
> dom0_gpa);
> >
> > gmfn = dom0_gpa >> 12;
> > mfn = gmfn_to_mfn(d, gmfn);
> > if ( !mfn_valid(mfn) ||
> > !get_page_and_type(mfn_to_page(mfn), d,
> PGT_writable_page) )
> > {
> > printk(XENLOG_G_WARNING
> > "Bad GMFN %lx (MFN %lx)\n", gmfn,
> mfn);
> > return 0;
> > }
> >
> > my_rd_wr_page = map_domain_page(mfn);
> >
> > /* Do your initialization of the page here; just
> write '2' in all bytes */
> > memset(my_rd_wr_page, 2, 1<<12);
> >
> > unmap_domain_page(my_rd_wr_page);
> > put_page_and_type(mfn_to_page(mfn));
> > break;
> >
> > default:
> > printk(XENLOG_G_DEBUG "%s:L%u: unhandled\n",
> > __FUNCTION__, __LINE__);
> > break;
> > }
> >
> > return 0;
> > }
> > ============================
> >
> > I have allocated a page from a sample dom0 kernel module (using
> vmalloc()), and passed the physical address of it to hypercall.
> >
> > void my_rd_wr_page_setup(void)
> > {
> > unsigned long my_gpa;
> > int err;
> > char *my_rd_wr_page = NULL;
> >
> > my_rd_wr_page = __vmalloc(
> > 1 * PAGE_SIZE,
> > GFP_KERNEL | __GFP_HIGHMEM,
> > __pgprot(__PAGE_KERNEL & ~_PAGE_NX));
> >
> > my_gpa = vmalloc_to_pfn((char *)&my_rd_wr_page) << PAGE_SHIFT;
>
> &my_rd_wr_page is the address of the variable (i.e. probably a pointer
> into the current stack) and not the address of the page you are trying
> to reference.
>
> Secondly vmalloc_to_pfn will return you a guest physical address, while
> hypercalls from PV guests always take an MFN.
>
> On the hypercall side your call to gmfn_to_mfn is normally an identity
> function for a PV guest which map_domain_page takes a machine address.
>
> So I think you need to launder the address through the p2m in the kernel
> before passing it to the hypercall.
>
> > printk("%s: Before Hypercall; my_rd_wr_page=%p my_gpa=%lx\n",
> __FUNCTION__, my_rd_wr_page, my_gpa);
> > memset(my_rd_wr_page, 0, PAGE_SIZE);
> > err = _hypercall2(int, my_rd_wr, 0x1, (void *)&my_gpa);
> > printk("%s: Hypercall returned; errno-%d\n", __FUNCTION__, err);
> > }
> >
> >
> > When I loaded the module, the following error has been observed:
> >
> > =============== On dom0 ===========
> > xen_features[0].writable_page_tables = 0
> > xen_features[0].writable_descriptor_tables = 0
> > xen_features[0].auto_translated_physmap = 0
> > xen_features[0].supervisor_mode_kernel = 0
> > xen_features[0].pae_pgdir_above_4gb = 1
> > my_rd_wr_page_setup: Before Hypercall; my_rd_wr_page=ffffc90010f7e000
> my_gpa=d7cf000
> > my_rd_wr_page_setup: Hypercall returned; errno-0
> > =====================================
> > On hypervisor:
> > (XEN) do_my_rd_wr:L178: GPA read 0xd7cf000
> > (XEN) mm.c:2037:d0 Error pfn d7cf: rd=ffff8300773c0000,
> od=0000000000000000, caf=180000000000000, taf=0000000000000000
> > (XEN) Bad GMFN d7cf (MFN d7cf)
> > ====================================
> >
> > From the dom0 messages (where i read the features), it looks like
> writable_page_tables is not set. Is it causing the issue in my case.
>
> Writable page tables is something else, it relates to how a _guest_ can
> update it's own page tables, not how Xen creates mappings of things.
>
> >
> > Could you please advice if i did something wrong here.
> > You are most welcome if you have completely different approach which
> works;
> >
> > Thanks a lot in advance
> >
> > Regards,
> > VSR.
>
>
>
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2011-06-06 13:28 How to share a page between dom0 and Hypervisror veerasena reddy
2011-06-06 13:53 ` Ian Campbell
2011-06-06 14:18 ` veerasena reddy
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