linux-kernel - Re: [PATCH v2 22/24] ext4: support verifying data from large folios with fs-verity

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Message-ID: <1360a439-8c95-41e4-840c-163685751110@huawei.com>
Date: Mon, 10 Nov 2025 20:08:59 +0800
From: Baokun Li <libaokun1@...wei.com>
To: Jan Kara <jack@...e.cz>, <libaokun@...weicloud.com>
CC: <linux-ext4@...r.kernel.org>, <tytso@....edu>, <adilger.kernel@...ger.ca>,
	<linux-kernel@...r.kernel.org>, <kernel@...kajraghav.com>,
	<mcgrof@...nel.org>, <ebiggers@...nel.org>, <willy@...radead.org>,
	<yi.zhang@...wei.com>, <yangerkun@...wei.com>, <chengzhihao1@...wei.com>
Subject: Re: [PATCH v2 22/24] ext4: support verifying data from large folios
 with fs-verity

On 2025-11-10 17:54, Jan Kara wrote:
> On Fri 07-11-25 22:42:47, libaokun@...weicloud.com wrote:
>> From: Baokun Li <libaokun1@...wei.com>
>>
>> Eric Biggers already added support for verifying data from large folios
>> several years ago in commit 5d0f0e57ed90 ("fsverity: support verifying
>> data from large folios").
>>
>> With ext4 now supporting large block sizes, the fs-verity tests
>> `kvm-xfstests -c ext4/64k -g verity -x encrypt` pass without issues.
>>
>> Therefore, remove the restriction and allow LBS to be enabled together
>> with fs-verity.
>>
>> Cc: Eric Biggers <ebiggers@...nel.org>
>> Signed-off-by: Baokun Li <libaokun1@...wei.com>
> Nice!
>
>> @@ -5175,7 +5173,8 @@ void ext4_set_inode_mapping_order(struct inode *inode)
>>  		return;
>>  
>>  	if (test_opt(inode->i_sb, DATA_FLAGS) == EXT4_MOUNT_JOURNAL_DATA ||
>> -	    ext4_test_inode_flag(inode, EXT4_INODE_JOURNAL_DATA))
>> +	    ext4_test_inode_flag(inode, EXT4_INODE_JOURNAL_DATA) ||
>> +	    ext4_has_feature_verity(inode->i_sb))
>>  		max_order = EXT4_SB(inode->i_sb)->s_min_folio_order;
>>  	else
>>  		max_order = EXT4_MAX_PAGECACHE_ORDER(inode);
> Is there a reason why fsverity needs the folio order to match the block
> size? I didn't find any by a quick glance. If yes, please state it in
> the changelog. If no, then I'd just use EXT4_MAX_PAGECACHE_ORDER() because
> it will give us some performance e.g. for mmapped executables protected by
> fsverify...
>
> 								Honza
>
There is no real limitation that prevents verity from using
EXT4_MAX_PAGECACHE_ORDER(). The reason I did not enable it by default
is that none of the filesystems supporting fs-verity had large folios
support at the time, and thus fs-verity with large folios has not yet
been tested in practice. For this reason, I only enabled it when LBS
is turned on.

As you pointed out, turning it on gives some performance gains. And
it also lets fs-verity get more testing. I’ll switch to
EXT4_MAX_PAGECACHE_ORDER(inode) in the next version.

Thank you for your review!


Cheers,
Baokun