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drivers: xen: unmap Enlighten page before jumping to Linux

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This commit fixes issue with usage of Xen hypervisor shared info page.
Previously U-boot did not unmap it at the end of OS boot process. Xen
did not prevent guest from this. So, it worked, but caused wierd
issues - one memory page, that was returned by memalign in U-boot
for Enlighten mapping was not unmaped by Xen (shared_info values was
not removed from there) and returned to allocator. During the Linux
boot, it uses shared_info page as regular RAM page, which leads to
hypervisor shared info corruption.

So, to fix this issue, as discussed on the xen-devel mailing list, the
code should:
   1) Unmap the page
   2) Populate the area with memory using XENMEM_populate_physmap

This patch adds page unmapping via XENMEM_remove_from_physmap, fills
hole in address space where page was mapped via XENMEM_populate_physmap
and return this address to memory allocator for freeing.

Signed-off-by: Dmytro Firsov <dmytro_firsov@epam.com>
Reviewed-by: Anastasiia Lukianenko <vicooodin@gmail.com>
This commit is contained in:
Dmytro Firsov 2022-07-19 14:55:28 +00:00 committed by Tom Rini
parent 032c9b045c
commit 0001a964b8
1 changed files with 31 additions and 0 deletions
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31
drivers/xen/hypervisor.c
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@ -144,6 +144,36 @@ struct shared_info *map_shared_info(void *p)
return HYPERVISOR_shared_info; return HYPERVISOR_shared_info;
} }
void unmap_shared_info(void)
{
xen_pfn_t shared_info_pfn = virt_to_pfn(HYPERVISOR_shared_info);
struct xen_remove_from_physmap xrfp = {0};
struct xen_memory_reservation reservation = {0};
xen_ulong_t nr_exts = 1;
xrfp.domid = DOMID_SELF;
xrfp.gpfn = shared_info_pfn;
if (HYPERVISOR_memory_op(XENMEM_remove_from_physmap, &xrfp) != 0)
panic("Failed to unmap HYPERVISOR_shared_info\n");
/*
* After removing from physmap there will be a hole in address space on
* HYPERVISOR_shared_info address, so to free memory allocated with
* memalign and prevent exceptions during access to this page we need to
* fill this 4KB hole with XENMEM_populate_physmap before jumping to Linux.
*/
reservation.domid = DOMID_SELF;
reservation.extent_order = 0;
reservation.address_bits = 0;
set_xen_guest_handle(reservation.extent_start, &shared_info_pfn);
reservation.nr_extents = nr_exts;
if (HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation) != nr_exts)
panic("Failed to populate memory on HYPERVISOR_shared_info addr\n");
/* Now we can return this to memory allocator */
free(HYPERVISOR_shared_info);
}
void do_hypervisor_callback(struct pt_regs *regs) void do_hypervisor_callback(struct pt_regs *regs)
{ {
unsigned long l1, l2, l1i, l2i; unsigned long l1, l2, l1i, l2i;
@ -251,4 +281,5 @@ void xen_fini(void)
fini_gnttab(); fini_gnttab();
fini_xenbus(); fini_xenbus();
fini_events(); fini_events();
unmap_shared_info();
} }