On Sat, Oct 18, 2025 at 01:17:56PM -0400, Pasha Tatashin wrote:
> KHO allocates metadata for its preserved memory map using the slab
> allocator via kzalloc(). This metadata is temporary and is used by the
> next kernel during early boot to find preserved memory.
>
> A problem arises when KFENCE is enabled. kzalloc() calls can be
> randomly intercepted by kfence_alloc(), which services the allocation
> from a dedicated KFENCE memory pool. This pool is allocated early in
> boot via memblock.
>
> When booting via KHO, the memblock allocator is restricted to a "scratch
> area", forcing the KFENCE pool to be allocated within it. This creates a
> conflict, as the scratch area is expected to be ephemeral and
> overwriteable by a subsequent kexec. If KHO metadata is placed in this
> KFENCE pool, it leads to memory corruption when the next kernel is
> loaded.
>
> To fix this, modify KHO to allocate its metadata directly from the buddy
> allocator instead of slab.
>
> Fixes: fc33e4b44b27 ("kexec: enable KHO support for memory preservation")
> Signed-off-by: Pasha Tatashin <[email protected]>
> Reviewed-by: Pratyush Yadav <[email protected]>
> ---
> kernel/liveupdate/kexec_handover.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/liveupdate/kexec_handover.c
> b/kernel/liveupdate/kexec_handover.c
> index 7c8e89a6b953..92662739a3a2 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -132,6 +132,8 @@ static struct kho_out kho_out = {
> .finalized = false,
> };
>
> +DEFINE_FREE(kho_free_page, void *, free_page((unsigned long)_T))
> +
Just drop kho_ prefix and stick it into include/linux/gfp.h:
DEFINE_FREE(free_page, void *, if (_T) free_page((unsigned long)_T))
> static void *xa_load_or_alloc(struct xarray *xa, unsigned long index)
> {
> void *res = xa_load(xa, index);
> @@ -139,7 +141,7 @@ static void *xa_load_or_alloc(struct xarray *xa, unsigned
> long index)
> if (res)
> return res;
>
> - void *elm __free(kfree) = kzalloc(PAGE_SIZE, GFP_KERNEL);
> + void *elm __free(kho_free_page) = (void *)get_zeroed_page(GFP_KERNEL);
>
> if (!elm)
> return ERR_PTR(-ENOMEM);
> @@ -352,9 +354,9 @@ static_assert(sizeof(struct khoser_mem_chunk) ==
> PAGE_SIZE);
> static struct khoser_mem_chunk *new_chunk(struct khoser_mem_chunk *cur_chunk,
> unsigned long order)
> {
> - struct khoser_mem_chunk *chunk __free(kfree) = NULL;
> + struct khoser_mem_chunk *chunk __free(kho_free_page) = NULL;
>
> - chunk = kzalloc(PAGE_SIZE, GFP_KERNEL);
> + chunk = (void *)get_zeroed_page(GFP_KERNEL);
> if (!chunk)
> return ERR_PTR(-ENOMEM);
>
> --
> 2.51.0.915.g61a8936c21-goog
>
--
Sincerely yours,
Mike.
