On 02/22/2019 03:27 AM, Cornelia Huck wrote:
On Thu, 21 Feb 2019 20:09:16 +0100
Halil Pasic <pasic@xxxxxxxxxxxxx> wrote:
On Thu, 21 Feb 2019 12:10:32 -0500
Eric Farman <farman@xxxxxxxxxxxxx> wrote:
Well, taking the TIC-boundary logic from tic_target_chain_exists() and
stuffing it into ccwchain_calc_length() seems to do the trick for seeing
if we're sending a TIC back into our current chain, and makes the dasd
boot work again (the following is built on top of this patch, and is
surely whitespace damaged):
diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
index ba08fe137c2e..a4abe7519b7e 100644
--- a/drivers/s390/cio/vfio_ccw_cp.c
+++ b/drivers/s390/cio/vfio_ccw_cp.c
@@ -362,6 +362,7 @@ static int ccwchain_calc_length(u64 iova, struct
channel_program *cp)
{
struct ccw1 *ccw, *p;
int cnt;
+ u64 tail;
/*
* Copy current chain from guest to host kernel.
@@ -392,7 +393,9 @@ static int ccwchain_calc_length(u64 iova, struct
channel_program *cp)
return -EOPNOTSUPP;
}
- if (!ccw_is_chain(ccw))
+ tail = iova + (cnt - 1) * sizeof(struct ccw1);
+
+ if (!(ccw_is_chain(ccw) || (ccw_is_tic(ccw) && iova <=
ccw->cda && ccw->cda <= tail)))
After De Morgan this looks like
!ccw_is_chain(ccw)) && !(ccw_is_tic(ccw) && tic_points_in_this_chain())
which only differs form the state without the Farhan fix by not carrying
on for tic's that point outside of this chain.
Would certainly catch the problem you discovered.
Of course there is no guarantee that this covers all the theoretically
possible cases where we could skip over a ccw that would terminate a chain
(tic or not chaining) if there was no status modifier. If you like I can
construct an example where this heuristic fails (at least I think so).
If this is the direction we are going to take I think "vfio-ccw: Don't
assume there are more ccws after a TIC" should be superseded by this. And
we need a comment that explains the second part of the expression.
As that patch is already queued, I think we should do that change with
'fixes' on top.
There are probably more corner cases that we're missing, but this fixes
a problem that can be hit today (well, with some posted patches...), so
I'd go ahead and queue it and go through the code and maybe fix/rework
on top.
Sounds good. I will get that posted so we can look it over with fresh eyes.
Did any of you do any stress testing of that change yet?
I've been running fio since yesterday after my last email (and
subsequent lunch), and haven't seen any further errors. It's still
running today, and knock on wood it'll keep going nicely.
It just occurred to me that I was trying to run a different set of tests
when I bumped into this. I think they are a different set of disks, so
I should go back and try that while fio runs.
- Eric
