On Thu, 24 Aug 2017 11:05:08 -0400
Farhan Ali <al...@linux.vnet.ibm.com> wrote:
> Hi,
>
> There is an issue in QEMU bios which is exposed by commit
>
> commit 198c0d1f9df8c429502cb744fc26b6ba6e71db74
> Author: Halil Pasic <pa...@linux.vnet.ibm.com>
> 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 <pa...@linux.vnet.ibm.com>
> Message-Id: <20170727154842.23427-1-pa...@linux.vnet.ibm.com>
> Reviewed-by: Dong Jia Shi <bjsdj...@linux.vnet.ibm.com>
> Signed-off-by: Cornelia Huck <coh...@redhat.com>
>
>
> 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.
I have not seen this problem on any of the systems I tested on (well, I
would not have merged this if I did...) - RHEL 7 and F26. Do we need a
dynamic allocation to guarantee alignment?
