Re: [PATCH] fsverity: add dependency on 64K or smaller pages

["Arnd Bergmann" <arnd@arndb.de>]

On Tue, Feb 24, 2026, at 14:55, David Sterba wrote:
> On Sat, Feb 21, 2026 at 12:45:25PM -0800, Eric Biggers wrote:
>> Currently, all filesystems that support fsverity (ext4, f2fs, and btrfs)
>> cache the Merkle tree in the pagecache at a 64K aligned offset after the
>> end of the file data.  This offset needs to be a multiple of the page
>> size, which is guaranteed only when the page size is 64K or smaller.
>> 
>> 64K was chosen to be the "largest reasonable page size".  But it isn't
>> the largest *possible* page size: the hexagon and powerpc ports of Linux
>> support 256K pages, though that configuration is rarely used.
>> 
>> For now, just disable support for FS_VERITY in these odd configurations
>> to ensure it isn't used in cases where it would have incorrect behavior.
>> 
>> Fixes: 671e67b47e9f ("fs-verity: add Kconfig and the helper functions for hashing")
>> Reported-by: Christoph Hellwig <hch@lst.de>
>> Closes: https://lore.kernel.org/r/20260119063349.GA643@lst.de
>> Signed-off-by: Eric Biggers <ebiggers@kernel.org>
>
> Makes sense to me, we have "depends on PAGE_SIZE_LESS_THAN_256KB" since
> somebody tried to use btrfs on the 256K system.

I wonder if we should just drop the configuration entirely. There
are very few users on either PowerPC44x (officially orphaned, but
I know users) and Hexagon (officially supported, but no hardware
available outside of Qualcomm). My impression is that this was
implemented purely because the hardware can do it, not because
anyone actually wants to use 256K pages.

I see that commit "e12401222f74 powerpc/44x: Support for 256KB
PAGE_SIZE" mentions how one has to patch the linker to support
larger than 64K pages, and I see that both powerpc and hexagon
linkers still hardcode the section alignment to 64K pages, for
obvious reasons.

      Arnd