[PATCH v3] KHO: Fix boot failure due to kmemleak access to non-PRESENT pages

[PATCH v3] KHO: Fix boot failure due to kmemleak access to non-PRESENT pages

[ranxiaokai627]

From: Ran Xiaokai <ran.xiaokai@zte.com.cn>

When booting with debug_pagealloc=on while having:
CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT=y
CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=n
the system fails to boot due to page faults during kmemleak scanning.

This occurs because:
With debug_pagealloc is enabled, __free_pages() invokes
debug_pagealloc_unmap_pages(), clearing the _PAGE_PRESENT bit for
freed pages in the kernel page table.
KHO scratch areas are allocated from memblock and noted by kmemleak. But
these areas don't remain reserved but released later to the page allocator
using init_cma_reserved_pageblock(). This causes subsequent kmemleak scans
access non-PRESENT pages, leading to fatal page faults.

Mark scratch areas with kmemleak_ignore_phys() after they are allocated
from memblock to exclude them from kmemleak scanning before they are
released to buddy allocator to fix this.

Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers")
Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 kernel/liveupdate/kexec_handover.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 224bdf5becb6..c729d455ee7b 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -11,6 +11,7 @@
 
 #include <linux/cleanup.h>
 #include <linux/cma.h>
+#include <linux/kmemleak.h>
 #include <linux/count_zeros.h>
 #include <linux/kexec.h>
 #include <linux/kexec_handover.h>
@@ -1369,6 +1370,7 @@ static __init int kho_init(void)
 		unsigned long count = kho_scratch[i].size >> PAGE_SHIFT;
 		unsigned long pfn;
 
+		kmemleak_ignore_phys(kho_scratch[i].addr);
 		for (pfn = base_pfn; pfn < base_pfn + count;
 		     pfn += pageblock_nr_pages)
 			init_cma_reserved_pageblock(pfn_to_page(pfn));
-- 
2.25.1

Re: [PATCH v3] KHO: Fix boot failure due to kmemleak access to non-PRESENT pages

[Pratyush Yadav]

On Mon, Nov 24 2025, ranxiaokai627@163.com wrote:

> From: Ran Xiaokai <ran.xiaokai@zte.com.cn>
>
> When booting with debug_pagealloc=on while having:
> CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT=y
> CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=n
> the system fails to boot due to page faults during kmemleak scanning.
>
> This occurs because:
> With debug_pagealloc is enabled, __free_pages() invokes
> debug_pagealloc_unmap_pages(), clearing the _PAGE_PRESENT bit for
> freed pages in the kernel page table.
> KHO scratch areas are allocated from memblock and noted by kmemleak. But
> these areas don't remain reserved but released later to the page allocator
> using init_cma_reserved_pageblock(). This causes subsequent kmemleak scans
> access non-PRESENT pages, leading to fatal page faults.
>
> Mark scratch areas with kmemleak_ignore_phys() after they are allocated
> from memblock to exclude them from kmemleak scanning before they are
> released to buddy allocator to fix this.
>
> Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers")
> Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
> Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
>  kernel/liveupdate/kexec_handover.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> index 224bdf5becb6..c729d455ee7b 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -11,6 +11,7 @@
>  
>  #include <linux/cleanup.h>
>  #include <linux/cma.h>
> +#include <linux/kmemleak.h>
>  #include <linux/count_zeros.h>
>  #include <linux/kexec.h>
>  #include <linux/kexec_handover.h>
> @@ -1369,6 +1370,7 @@ static __init int kho_init(void)
>  		unsigned long count = kho_scratch[i].size >> PAGE_SHIFT;
>  		unsigned long pfn;
>  
> +		kmemleak_ignore_phys(kho_scratch[i].addr);

Can you please put the explanation you gave in [0] for why this is not
necessary in KHO boot as a comment here?

After that,

Reviewed-by: Pratyush Yadav <pratyush@kernel.org>

[0] https://lore.kernel.org/all/20251122175735.92578-1-ranxiaokai627@163.com/

>  		for (pfn = base_pfn; pfn < base_pfn + count;
>  		     pfn += pageblock_nr_pages)
>  			init_cma_reserved_pageblock(pfn_to_page(pfn));

-- 
Regards,
Pratyush Yadav

Re: [PATCH v3] KHO: Fix boot failure due to kmemleak access to non-PRESENT pages

[Pratyush Yadav]

On Mon, Nov 24 2025, Pratyush Yadav wrote:

> On Mon, Nov 24 2025, ranxiaokai627@163.com wrote:
>
>> From: Ran Xiaokai <ran.xiaokai@zte.com.cn>
>>
>> When booting with debug_pagealloc=on while having:
>> CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT=y
>> CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=n
>> the system fails to boot due to page faults during kmemleak scanning.
>>
>> This occurs because:
>> With debug_pagealloc is enabled, __free_pages() invokes
>> debug_pagealloc_unmap_pages(), clearing the _PAGE_PRESENT bit for
>> freed pages in the kernel page table.
>> KHO scratch areas are allocated from memblock and noted by kmemleak. But
>> these areas don't remain reserved but released later to the page allocator
>> using init_cma_reserved_pageblock(). This causes subsequent kmemleak scans
>> access non-PRESENT pages, leading to fatal page faults.
>>
>> Mark scratch areas with kmemleak_ignore_phys() after they are allocated
>> from memblock to exclude them from kmemleak scanning before they are
>> released to buddy allocator to fix this.
>>
>> Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers")
>> Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
>> Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
>> ---
>>  kernel/liveupdate/kexec_handover.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
>> index 224bdf5becb6..c729d455ee7b 100644
>> --- a/kernel/liveupdate/kexec_handover.c
>> +++ b/kernel/liveupdate/kexec_handover.c
>> @@ -11,6 +11,7 @@
>>  
>>  #include <linux/cleanup.h>
>>  #include <linux/cma.h>
>> +#include <linux/kmemleak.h>
>>  #include <linux/count_zeros.h>
>>  #include <linux/kexec.h>
>>  #include <linux/kexec_handover.h>
>> @@ -1369,6 +1370,7 @@ static __init int kho_init(void)
>>  		unsigned long count = kho_scratch[i].size >> PAGE_SHIFT;
>>  		unsigned long pfn;
>>  
>> +		kmemleak_ignore_phys(kho_scratch[i].addr);
>
> Can you please put the explanation you gave in [0] for why this is not
> necessary in KHO boot as a comment here?

And also an explanation of why this is necessary in the first place. You
do explain that in the commit message, but a shorter version as a
comment will make this a lot easier to understand instead of having to
dig through git history.

[...]

-- 
Regards,
Pratyush Yadav