Re: [PATCH v2] mm/swap: fix SWP_PFN_BITS with CONFIG_PHYS_ADDR_T_64BIT on 32bit

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 07.12.22 23:40, Yang Shi wrote:
On Tue, Dec 6, 2022 at 2:57 AM David Hildenbrand <david@xxxxxxxxxx> wrote:

We use "unsigned long" to store a PFN in the kernel and phys_addr_t to
store a physical address.

On a 64bit system, both are 64bit wide. However, on a 32bit system, the
latter might be 64bit wide. This is, for example, the case on x86 with
PAE: phys_addr_t and PTEs are 64bit wide, while "unsigned long" only
spans 32bit.

The current definition of SWP_PFN_BITS without MAX_PHYSMEM_BITS misses
that case, and assumes that the maximum PFN is limited by an 32bit
phys_addr_t. This implies, that SWP_PFN_BITS will currently only be able to
cover 4 GiB - 1 on any 32bit system with 4k page size, which is wrong.

Thanks for debugging this. IIUC this means even swap is actually
broken on x86_32 + PAE?

I saw all different kinds of issues while testing debugging without this patch, but they might just be a fallout from previous page migration/THP splitting issues.

I think swap should be fine, because SWP_PFN_BITS only affects swp_offset_pfn(): only used when is_pfn_swap_entry()==true.

Thanks!

--
Thanks,

David / dhildenb





[Index of Archives]     [Linux ARM Kernel]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [IETF Annouce]     [Bugtraq]     [Linux OMAP]     [Linux MIPS]     [eCos]     [Asterisk Internet PBX]     [Linux API]

  Powered by Linux