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Re: [PATCH] efidisk: pass buffers with higher alignment
From: |
Stefan Agner |
Subject: |
Re: [PATCH] efidisk: pass buffers with higher alignment |
Date: |
Mon, 09 May 2022 20:55:21 +0200 |
User-agent: |
Roundcube Webmail/1.4.9 |
On 2022-05-05 17:42, Vladimir 'phcoder' Serbinenko wrote:
> Le jeu. 5 mai 2022, 15:55, Stefan Agner <stefan@agner.ch> a écrit :
>
>> Despite the UEFI specification saying "the requirement is that the
>> start address of a buffer must be evenly divisible by IoAlign with
>> no remainder.", it seems that a higher alignment requirement is
>> neecssary on some system (e.g. a Intel NUC system with NVMe SSD).
>> That particular system has IoAlign set to 2, and sometimes returns
>> status 7 when buffers with alignment of 2 are passed. Things seem
>> to work fine with buffers aligned to 4 bytes.
>>
>> It seems that IoAlign > 1 means 2 ^ IoAlign. There is also such a hint
>> in an example printed in the Driver Writer's Guide:
>> ScsiPassThruMode.IoAlign = 2; // Data must be alligned on 4-byte boundary
>>
>> Pass 2 ^ IoAlign aligned buffers to make sure GRUB2 works properly on
>> all systems.
>>
>> Note: The problem has only noticed with compressed squashfs. It seems
>> that ext4 (and presumably other file system drivers) pass buffers with
>> a higher alignment already.
>>
>> Signed-off-by: Stefan Agner <stefan@agner.ch>
>> ---
>> grub-core/disk/efi/efidisk.c | 12 ++++++++++--
>> 1 file changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/grub-core/disk/efi/efidisk.c b/grub-core/disk/efi/efidisk.c
>> index f077b5f55..0fc2f0826 100644
>> --- a/grub-core/disk/efi/efidisk.c
>> +++ b/grub-core/disk/efi/efidisk.c
>> @@ -553,8 +553,16 @@ grub_efidisk_readwrite (struct grub_disk *disk,
>> grub_disk_addr_t sector,
>> d = disk->data;
>> bio = d->block_io;
>>
>> - /* Set alignment to 1 if 0 specified */
>> - io_align = bio->media->io_align ? bio->media->io_align : 1;
>> + /*
>> + * If IoAlign is > 1, it means alignment by 2^IoAlign
>> + * Note: UEFI spec claims alignment by IoAlign. But there are systems
>> + * with IoAlign=2 which return status 7 if 2 bytes aligned buffers are
>> + * passed.
>> + */
>> + if (bio->media->io_align > 1)
>> + io_align = 1 << bio->media->io_align;
>> + else
>> + io_align = 1;
>
> May be it should be >=1 rather than > 1?
>
No, 1 is explicitly defined to mean no alignment, hence io_align needs
to be set to 1.
--
Stefan
>> num_bytes = size << disk->log_sector_size;
>>
>> if ((grub_addr_t) buf & (io_align - 1))
>> --
>> 2.36.0
>>
>> _______________________________________________
>> Grub-devel mailing list
>> Grub-devel@gnu.org
>> https://lists.gnu.org/mailman/listinfo/grub-devel
>
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