Re: [Qemu-devel] S390 bios breaks in qemu 2.10.rc3

[Christian Borntraeger]

Just to understand the urgency. Is the problem happening with the BIOS that is 
shipped in the
upstream git tree, or a self-built one?


On 08/24/2017 05:05 PM, Farhan Ali wrote:
> Hi,
> 
> There is an issue in QEMU bios which is exposed by commit
> 
> commit 198c0d1f9df8c429502cb744fc26b6ba6e71db74
> Author: Halil Pasic <address@hidden>
> Date:   Thu Jul 27 17:48:42 2017 +0200
> 
>     s390x/css: check ccw address validity
> 
>     According to the PoP channel command words (CCW) must be doubleword
>     aligned and 31 bit addressable for format 1 and 24 bit addressable for
>     format 0 CCWs.
> 
>     If the channel subsystem encounters a ccw address which does not satisfy
>     this alignment requirement a program-check condition is recognised.
> 
>     The situation with 31 bit addressable is a bit more complicated: both the
>     ORB and a format 1 CCW TIC hold the address of (the rest of) the channel
>     program, that is the address of the next CCW in a word, and the PoP
>     mandates that bit 0 of that word shall be zero -- or a program-check
>     condition is to be recognized -- and does not belong to the field holding
>     the ccw address.
> 
>     Since in code the corresponding fields span across the whole word (unlike
>     in PoP where these are defined as 31 bit wide) we can check this by
>     applying a mask. The 24 addressable case isn't affecting TIC because the
>     address is composed of a halfword and a byte portion (no additional zero
>     bit requirements) and just slightly complicates the ORB case where also
>     bits 1-7 need to be zero.
> 
>     The same requirements (especially n-bit addressability) apply to the
>     ccw addresses generated while chaining.
> 
>     Let's make our CSS implementation follow the AR more closely.
> 
>     Signed-off-by: Halil Pasic <address@hidden>
>     Message-Id: <address@hidden>
>     Reviewed-by: Dong Jia Shi <address@hidden>
>     Signed-off-by: Cornelia Huck <address@hidden>
> 
> 
> It looks like the bios does not create a double word aligned CCW. Looking at 
> the bios code we the CCW1 struct is not aligned
> 
> /* channel command word (type 1) */
> struct ccw1 {
>     __u8 cmd_code;
>     __u8 flags;
>     __u16 count;
>     __u32 cda;
> } __attribute__ ((packed));
> 
> and it looks like the compiler does not guarantee a doubleword alignment.
> 
> The weird thing about it is I see it break in one of my system and works fine 
> in another system. Trying a simple fix of aligning the struct also doesn't 
> seem to work all the time.
> 
> 
> Thanks
> Farhan
>