arm64: mm: Correct the update of max_pfn

[PATCH] arm64: mm: Correct the update of max_pfn

Posted by Zhenhua Huang 10 months, 3 weeks ago

Hotplugged memory can be smaller than the original memory. For example,
on my target:

root@genericarmv8:~# cat /sys/kernel/debug/memblock/memory
   0: 0x0000000064005000..0x0000000064023fff    0 NOMAP
   1: 0x0000000064400000..0x00000000647fffff    0 NOMAP
   2: 0x0000000068000000..0x000000006fffffff    0 DRV_MNG
   3: 0x0000000088800000..0x0000000094ffefff    0 NONE
   4: 0x0000000094fff000..0x0000000094ffffff    0 NOMAP
max_pfn will affect read_page_owner. Therefore, it should first compare and
then select the larger value for max_pfn.

Fixes: 8fac67ca236b ("arm64: mm: update max_pfn after memory hotplug")
Signed-off-by: Zhenhua Huang <quic_zhenhuah@quicinc.com>
---
 arch/arm64/mm/mmu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 1dfe1a8efdbe..310ff75891ef 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1361,7 +1361,8 @@ int arch_add_memory(int nid, u64 start, u64 size,
 		__remove_pgd_mapping(swapper_pg_dir,
 				     __phys_to_virt(start), size);
 	else {
-		max_pfn = PFN_UP(start + size);
+		/* Address of hotplugged memory can be smaller */
+		max_pfn = max(max_pfn, PFN_UP(start + size));
 		max_low_pfn = max_pfn;
 	}
 
-- 
2.25.1

Re: [PATCH] arm64: mm: Correct the update of max_pfn

Posted by Catalin Marinas 10 months, 2 weeks ago

On Fri, 21 Mar 2025 15:00:19 +0800, Zhenhua Huang wrote:
> Hotplugged memory can be smaller than the original memory. For example,
> on my target:
> 
> root@genericarmv8:~# cat /sys/kernel/debug/memblock/memory
>    0: 0x0000000064005000..0x0000000064023fff    0 NOMAP
>    1: 0x0000000064400000..0x00000000647fffff    0 NOMAP
>    2: 0x0000000068000000..0x000000006fffffff    0 DRV_MNG
>    3: 0x0000000088800000..0x0000000094ffefff    0 NONE
>    4: 0x0000000094fff000..0x0000000094ffffff    0 NOMAP
> max_pfn will affect read_page_owner. Therefore, it should first compare and
> then select the larger value for max_pfn.
> 
> [...]

Applied to arm64 (for-next/core), thanks!

[1/1] arm64: mm: Correct the update of max_pfn
      https://git.kernel.org/arm64/c/89f43e1ce6f6

-- 
Catalin

Re: [PATCH] arm64: mm: Correct the update of max_pfn

Posted by David Hildenbrand 10 months, 2 weeks ago

On 21.03.25 08:00, Zhenhua Huang wrote:
> Hotplugged memory can be smaller than the original memory. For example,
> on my target:
> 
> root@genericarmv8:~# cat /sys/kernel/debug/memblock/memory
>     0: 0x0000000064005000..0x0000000064023fff    0 NOMAP
>     1: 0x0000000064400000..0x00000000647fffff    0 NOMAP
>     2: 0x0000000068000000..0x000000006fffffff    0 DRV_MNG
>     3: 0x0000000088800000..0x0000000094ffefff    0 NONE
>     4: 0x0000000094fff000..0x0000000094ffffff    0 NOMAP
> max_pfn will affect read_page_owner. Therefore, it should first compare and
> then select the larger value for max_pfn.
> 
> Fixes: 8fac67ca236b ("arm64: mm: update max_pfn after memory hotplug")
> Signed-off-by: Zhenhua Huang <quic_zhenhuah@quicinc.com>
> ---
>   arch/arm64/mm/mmu.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 1dfe1a8efdbe..310ff75891ef 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1361,7 +1361,8 @@ int arch_add_memory(int nid, u64 start, u64 size,
>   		__remove_pgd_mapping(swapper_pg_dir,
>   				     __phys_to_virt(start), size);
>   	else {
> -		max_pfn = PFN_UP(start + size);
> +		/* Address of hotplugged memory can be smaller */
> +		max_pfn = max(max_pfn, PFN_UP(start + size));
>   		max_low_pfn = max_pfn;
>   	}
>   

Yes, that's the right thing to do. (I always wonder if these values 
should be atomically updated ...)

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb

Re: [PATCH] arm64: mm: Correct the update of max_pfn

Posted by Anshuman Khandual 10 months, 3 weeks ago

On 3/21/25 12:30, Zhenhua Huang wrote:
> Hotplugged memory can be smaller than the original memory. For example,
> on my target:
> 
> root@genericarmv8:~# cat /sys/kernel/debug/memblock/memory
>    0: 0x0000000064005000..0x0000000064023fff    0 NOMAP
>    1: 0x0000000064400000..0x00000000647fffff    0 NOMAP
>    2: 0x0000000068000000..0x000000006fffffff    0 DRV_MNG
>    3: 0x0000000088800000..0x0000000094ffefff    0 NONE
>    4: 0x0000000094fff000..0x0000000094ffffff    0 NOMAP
> max_pfn will affect read_page_owner. Therefore, it should first compare and
> then select the larger value for max_pfn.
> 
> Fixes: 8fac67ca236b ("arm64: mm: update max_pfn after memory hotplug")
> Signed-off-by: Zhenhua Huang <quic_zhenhuah@quicinc.com>
> ---
>  arch/arm64/mm/mmu.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 1dfe1a8efdbe..310ff75891ef 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1361,7 +1361,8 @@ int arch_add_memory(int nid, u64 start, u64 size,
>  		__remove_pgd_mapping(swapper_pg_dir,
>  				     __phys_to_virt(start), size);
>  	else {
> -		max_pfn = PFN_UP(start + size);
> +		/* Address of hotplugged memory can be smaller */
> +		max_pfn = max(max_pfn, PFN_UP(start + size));
>  		max_low_pfn = max_pfn;
>  	}
>  

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>

Re: [PATCH] arm64: mm: Correct the update of max_pfn

Posted by David Hildenbrand 10 months, 3 weeks ago

On 21.03.25 08:00, Zhenhua Huang wrote:
> Hotplugged memory can be smaller than the original memory. For example,
> on my target:
> 
> root@genericarmv8:~# cat /sys/kernel/debug/memblock/memory
>     0: 0x0000000064005000..0x0000000064023fff    0 NOMAP
>     1: 0x0000000064400000..0x00000000647fffff    0 NOMAP
>     2: 0x0000000068000000..0x000000006fffffff    0 DRV_MNG
>     3: 0x0000000088800000..0x0000000094ffefff    0 NONE
>     4: 0x0000000094fff000..0x0000000094ffffff    0 NOMAP
> max_pfn will affect read_page_owner. Therefore, it should first compare and
> then select the larger value for max_pfn.
> 
> Fixes: 8fac67ca236b ("arm64: mm: update max_pfn after memory hotplug")
> Signed-off-by: Zhenhua Huang <quic_zhenhuah@quicinc.com>
> ---
>   arch/arm64/mm/mmu.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 1dfe1a8efdbe..310ff75891ef 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1361,7 +1361,8 @@ int arch_add_memory(int nid, u64 start, u64 size,
>   		__remove_pgd_mapping(swapper_pg_dir,
>   				     __phys_to_virt(start), size);
>   	else {
> -		max_pfn = PFN_UP(start + size);
> +		/* Address of hotplugged memory can be smaller */
> +		max_pfn = max(max_pfn, PFN_UP(start + size));
>   		max_low_pfn = max_pfn;
>   	}
>   

Acked-by: David Hildenbrand <david@redhat.com>


-- 
Cheers,

David / dhildenb

Re: [PATCH] arm64: mm: Correct the update of max_pfn

Posted by Catalin Marinas 10 months, 3 weeks ago

On Fri, Mar 21, 2025 at 03:00:19PM +0800, Zhenhua Huang wrote:
> Hotplugged memory can be smaller than the original memory. For example,
> on my target:
> 
> root@genericarmv8:~# cat /sys/kernel/debug/memblock/memory
>    0: 0x0000000064005000..0x0000000064023fff    0 NOMAP
>    1: 0x0000000064400000..0x00000000647fffff    0 NOMAP
>    2: 0x0000000068000000..0x000000006fffffff    0 DRV_MNG
>    3: 0x0000000088800000..0x0000000094ffefff    0 NONE
>    4: 0x0000000094fff000..0x0000000094ffffff    0 NOMAP
> max_pfn will affect read_page_owner. Therefore, it should first compare and
> then select the larger value for max_pfn.
> 
> Fixes: 8fac67ca236b ("arm64: mm: update max_pfn after memory hotplug")
> Signed-off-by: Zhenhua Huang <quic_zhenhuah@quicinc.com>
> ---
>  arch/arm64/mm/mmu.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 1dfe1a8efdbe..310ff75891ef 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1361,7 +1361,8 @@ int arch_add_memory(int nid, u64 start, u64 size,
>  		__remove_pgd_mapping(swapper_pg_dir,
>  				     __phys_to_virt(start), size);
>  	else {
> -		max_pfn = PFN_UP(start + size);
> +		/* Address of hotplugged memory can be smaller */
> +		max_pfn = max(max_pfn, PFN_UP(start + size));
>  		max_low_pfn = max_pfn;
>  	}

I think this makes sense and also matches what x86 does. I'll queue it
at -rc1 as a fix.

Thanks.

-- 
Catalin