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

["David Hildenbrand (Arm)" <david@kernel.org>]

On 10/10/26 18:20, 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)) {

That looks rather hacky as well.

I really don't want us to have various source of poison information that the
page allocator + core-mm has to mess with. It's just very bad design.

I made that clear in the last kexec attempt to do something similar.

This likely belongs into memory onlining, which could online only the relevant,
un-poisoned pageblocks.

Not sure how it would best retrieve that information, but we should definitely
not add more shaky hwpoison sources to random pieces of core kernel code.

-- 
Cheers,

David