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.