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_fir...@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] -- Regards, Oleksandr Tyshchenko
