veerasena reddy
2011-Jun-06 13:28 UTC
[Xen-devel] How to share a page between dom0 and Hypervisror
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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Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel
Ian Campbell
2011-Jun-06 13:53 UTC
Re: [Xen-devel] How to share a page between dom0 and Hypervisror
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._______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
veerasena reddy
2011-Jun-06 14:18 UTC
Re: [Xen-devel] How to share a page between dom0 and Hypervisror
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. > > >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel