[PATCH] efidisk: pass buffers with higher alignment

[Stefan Agner]

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;
   num_bytes = size << disk->log_sector_size;
 
   if ((grub_addr_t) buf & (io_align - 1))
-- 
2.36.0