From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Mon, 6 May 2019 16:47:10 +0200 From: Cornelia Huck Subject: Re: [PATCH 1/7] s390/cio: Update SCSW if it points to the end of the chain Message-ID: <20190506164710.5fe0b6c8.cohuck@redhat.com> In-Reply-To: <20190503134912.39756-2-farman@linux.ibm.com> References: <20190503134912.39756-1-farman@linux.ibm.com> <20190503134912.39756-2-farman@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: kvm-owner@vger.kernel.org List-Archive: List-Post: To: Eric Farman Cc: Farhan Ali , Halil Pasic , Pierre Morel , linux-s390@vger.kernel.org, kvm@vger.kernel.org List-ID: On Fri, 3 May 2019 15:49:06 +0200 Eric Farman wrote: > Per the POPs [1], when processing an interrupt the SCSW.CPA field of an > IRB generally points to 8 bytes after the last CCW that was executed > (there are exceptions, but this is the most common behavior). > > In the case of an error, this points us to the first un-executed CCW > in the chain. But in the case of normal I/O, the address points beyond > the end of the chain. While the guest generally only cares about this > when possibly restarting a channel program after error recovery, we > should convert the address even in the good scenario so that we provide > a consistent, valid, response upon I/O completion. > > [1] Figure 16-6 in SA22-7832-11. The footnotes in that table also state > that this is true even if the resulting address is invalid or protected, > but moving to the end of the guest chain should not be a surprise. > > Signed-off-by: Eric Farman > --- > drivers/s390/cio/vfio_ccw_cp.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c > index 384b3987eeb4..f86da78eaeaa 100644 > --- a/drivers/s390/cio/vfio_ccw_cp.c > +++ b/drivers/s390/cio/vfio_ccw_cp.c > @@ -870,7 +870,7 @@ void cp_update_scsw(struct channel_program *cp, union scsw *scsw) > */ > list_for_each_entry(chain, &cp->ccwchain_list, next) { > ccw_head = (u32)(u64)chain->ch_ccw; > - if (is_cpa_within_range(cpa, ccw_head, chain->ch_len)) { > + if (is_cpa_within_range(cpa, ccw_head, chain->ch_len + 1)) { Maybe add a comment /* On successful execution, cpa points just beyond the end of the chain. */ or so, to avoid head-scratching and PoP-reading in the future? > /* > * (cpa - ccw_head) is the offset value of the host > * physical ccw to its chain head.