RE: Dell BIOS issue reading Disk Extended data

[Limonciello, Mario]

> 
> Hello Dell folks, I'm Guilherme Piccoli from Canonical - first of all,
> apologies for the out-of-nowhere communication. We've been investigating
> an issue that seems to date long time ago, and eventually we could
> narrow it to what appears to be a Dell BIOS bug. Notice I'm also looping
> a kernel x86 ML and grub-devel, just for the purpose of archiving such
> discussion in public lists, to help others that may find such an issue
> in the future.
> 
> Since I don't have contacts of Dell representatives, I've just raised a
> list of people from Dell contributing to kernel in the last 2 years -
> maybe one of you could point me towards the path of a proper
> contact/channel to discuss such an issue. If not, I'm sorry for the noise.
> Let me detail the problem we're observing - notice all of this is about
> legacy BIOS mode, not UEFI.

Most of the guys you CC'ed from Dell work on client related things, not
servers.  So I'll move some of the client guys off of this thread into BCC.
@K, Narendra can you please raise this with the appropriate team?

> 
> After creating a HW RAID on a Dell PowerEdge R730 (RAID5, total of 8T),
> GRUB fails to load its modules, dropping to "rescue mode". After a lot
> of investigation, we narrowed the issue to a bad return from BIOS to
> service 48h, int 13h [0] - this is the way GRUB collects disk size
> information. To double-check that, I've booted Linux in 16-bit realmode
> and with that, I could observe that EDD module [1] gets the same wrong
> value as total sectors - both GRUB and kernel EDD returns 0xFFFFFFFF.
> The correct value would be 0x3A3600000 according to SCSI Read Capacity
> 16 command (tested through the sg_readcap tool). In the P.S. session
> below there are details of the outputs collected by GRUB
> instrumentation, kernel EDD and sg_readcap tool.
> 
> There are some workarounds to that, like having a smaller partition
> _before_ the rootfs in the disk topology, to hold grub modules and
> linux/initrd images - in that case it seems the BIOS responds the int
> 13h/48h service with proper values, but this issue dates from a while
> ago [3][4], so I'm hereby seeking a proper discussion with Dell firmware
> engineers to understand if that could be fixed or at least to understand
> the root cause of such limitation.
> Thanks in advance,
> 
> 
> Guilherme
> 
> 
> [0]
> https://en.wikipedia.org/wiki/INT_13H#INT_13h_AH=48h:_Extended_Read_Drive_Para
> meters
> 
> [1]
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x
> 86/boot/edd.c
> 
> [2] https://askubuntu.com/q/867047
> 
> [3] https://askubuntu.com/q/416418
> 
> 
> P.S. GRUB debug output [dump of struct grub_biosdisk_drp in
> grub_biosdisk_get_diskinfo_real() function]:
> 
> size=1e, flags=9
> cyl=0, heads=0, sec=0
> bytesp_s=200, total=ffffffff,
> 
> 
> kernel EDD output:
> [    0.741378] edd[0]->total_secs=ffffffff
> 
> 
> sg_readcap output:
> $ sg_readcap /dev/sdb
> READ CAPACITY (10) indicates device capacity too large
>   now trying 16 byte cdb variant
> Read Capacity results:
>    Protection: prot_en=0, p_type=0, p_i_exponent=0
>    Logical block provisioning: lbpme=0, lbprz=0
>    Last logical block address=15625879551 (0x3a35fffff), Number of
> logical blocks=15625879552
> [...]