Re: [RFC PATCH 4/5] mm/page_alloc: Keep pre-online poison out of the buddy allocator

[Richard Cheng <icheng@nvidia.com>]

On Sat, Oct 10, 2026 at 09:50:12PM +0800, Shaikh Kamaluddin wrote:
> The inherited-poison path checks initialized blocks before releasing
> them to the buddy allocator. CXL device poison discovered before
> hot-added memory is onlined is recorded separately in the pre-online
> poison registry.
> 
> Extend __free_pages_core() to send a block to free_poisoned_block() when
> it intersects either poison source. In free_poisoned_block(), withhold a
> page when its PFN is registered as pre-online poison or its physical
> address is present in the inherited-poison table.
> 
> Pages identified by either source continue through
> hwpoison_boot_page(), while clean pages are released through
> accept_and_free_block().
> 
> Signed-off-by: Shaikh Kamaluddin <shaikhkamal2012@gmail.com>
> ---
>  mm/page_alloc.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index cca67a2702a4..57843df01b2a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -33,6 +33,7 @@
>  #include <linux/cpuset.h>
>  #include <linux/folio_batch.h>
>  #include <linux/memory_hotplug.h>
> +#include <linux/memory-failure.h>
>  #include <linux/nodemask.h>
>  #include <linux/vmstat.h>
>  #include <linux/fault-inject.h>
> @@ -1601,12 +1602,14 @@ static void __meminit free_poisoned_block(struct page *page, unsigned int order,
>  					  enum meminit_context context)
>  {
>  	unsigned long i, nr_pages = 1UL << order;
> +	unsigned long pfn = page_to_pfn(page);
>  
>  	for (i = 0; i < nr_pages; i++) {
>  		struct page *p = page + i;
>  		phys_addr_t phys = page_to_phys(p);
>  
> -		if (range_contains_poisoned_memory(phys, PAGE_SIZE)) {
> +		if (range_contains_poisoned_memory(phys, PAGE_SIZE) ||
> +		    preonline_hwpoison_contains(pfn + i)) {
>  			hwpoison_boot_page(p, context);
>  			continue;
>  		}
> @@ -1652,7 +1655,8 @@ void __meminit __free_pages_core(struct page *page, unsigned int order,
>  
>  	/* First: a block parked by __free_unaccepted() never returns here. */
>  	if (range_contains_poisoned_memory(page_to_phys(page),
> -					   PAGE_SIZE << order)) {
> +					   PAGE_SIZE << order) ||
> +	    preonline_hwpoison_intersects(page_to_pfn(page), nr_pages)) {
>  		free_poisoned_block(page, order, context);
>  		return;
>  	}
> -- 
> 2.43.0
>

Hi Shaikh,

I think the idea of discovering device poison first is good, but the boundary
should be more strictly designed.

Now if I don't get it wrong, if we turn on memory_hotplug.memmap_on_memory,
we can have part of CXL memory to do the bookkeeping for itself, without
using the existing RAM.

What if that bookkeeping part is poisoned ? the check ignores this situation
right ?

What about draw a clear line between normal RAM and hot-add CXL memory, have
the latter gone through the thorough check and do the rest you want ?

Best regards,
Richard Cheng.