From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH 1/7] s390/cio: Update SCSW if it points to the end of the chain References: <20190503134912.39756-1-farman@linux.ibm.com> <20190503134912.39756-2-farman@linux.ibm.com> <20190506164710.5fe0b6c8.cohuck@redhat.com> From: Eric Farman Date: Mon, 6 May 2019 11:23:51 -0400 MIME-Version: 1.0 In-Reply-To: <20190506164710.5fe0b6c8.cohuck@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: Sender: kvm-owner@vger.kernel.org List-Archive: List-Post: To: Cornelia Huck Cc: Farhan Ali , Halil Pasic , Pierre Morel , linux-s390@vger.kernel.org, kvm@vger.kernel.org List-ID: On 5/6/19 10:47 AM, Cornelia Huck wrote: > 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? And deny future visitors the confusion? :) Good point; added. > >> /* >> * (cpa - ccw_head) is the offset value of the host >> * physical ccw to its chain head. >