From 0001a964b840a62c66da42a89a10a2656831aa4b Mon Sep 17 00:00:00 2001
From: Dmytro Firsov <Dmytro_Firsov@epam.com>
Date: Tue, 19 Jul 2022 14:55:28 +0000
Subject: [PATCH] drivers: xen: unmap Enlighten page before jumping to Linux
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>
---
drivers/xen/hypervisor.c | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)
diff --git a/drivers/xen/hypervisor.c b/drivers/xen/hypervisor.c
index 2560894832..16c7c96c94 100644
--- a/drivers/xen/hypervisor.c
+++ b/drivers/xen/hypervisor.c
@@ -144,6 +144,36 @@ struct shared_info *map_shared_info(void *p)
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)
{
unsigned long l1, l2, l1i, l2i;
@@ -251,4 +281,5 @@ void xen_fini(void)
fini_gnttab();
fini_xenbus();
fini_events();
+ unmap_shared_info();
}
--
2.39.5