On 19.07.22 17:55, Dmytro Firsov wrote:
Hello Dmytro
First of all, thanks for fixing this issue.
Patch looks good, just a nit below.
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
Changes in v2:
- Reword commit message to be more clear with purpose of the patch
- Change BUG() helper to panic() and add error messages
- Add struct zeroing during initialization
- Fix typo in comment
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;
I think the explicit field's zeroing could be dropped now.
[snip]