On Tue, Apr 22, 2025 at 03:17:17PM +0200, Juergen Gross wrote:
Recently _pgd_alloc() was switched from using __get_free_pages() to pagetable_alloc_noprof(), which might return a compound page in case the allocation order is larger than 0.
On x86 this will be the case if CONFIG_MITIGATION_PAGE_TABLE_ISOLATION is set, even if PTI has been disabled at runtime.
When running as a Xen PV guest (this will always disable PTI), using a compound page for a PGD will result in VM_BUG_ON_PGFLAGS being triggered when the Xen code tries to pin the PGD.
Fix the Xen issue together with the not needed 8k allocation for a PGD with PTI disabled by replacing PGD_ALLOCATION_ORDER with an inline helper returning the needed order for PGD allocations.
Reported-by: Petr Vaněk arkamar@atlas.cz Fixes: a9b3c355c2e6 ("asm-generic: pgalloc: provide generic __pgd_{alloc,free}") Cc: stable@vger.kernel.org Signed-off-by: Juergen Gross jgross@suse.com
V2:
- use pgd_allocation_order() instead of PGD_ALLOCATION_ORDER (Dave Hansen)
The patch fixes the reported issue. The following trailers can be appended to the commit message (as per [1]):
Closes: https://lore.kernel.org/lkml/202541612720-Z_-deOZTOztMXHBh-arkamar@atlas.cz/ Tested-by: Petr Vaněk arkamar@atlas.cz
Cheers, Petr
[1] https://docs.kernel.org/process/5.Posting.html#patch-formatting-and-changelo...