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Fri, 16 Jan 2026 17:01:06 +0000 (GMT) Date: Fri, 16 Jan 2026 18:01:05 +0100 From: Claudio Imbrenda To: Eric Farman Cc: Janosch Frank , Christian Borntraeger , David Hildenbrand , Christoph Schlameuss , kvm@vger.kernel.org, linux-s390@vger.kernel.org Subject: Re: [PATCH] KVM: s390: vsie: retry SIE when unable to get vsie_page Message-ID: <20260116180105.1e37f926@p-imbrenda> In-Reply-To: <3d997b2645c80396c0f7c69f95fd8ec0d4784b20.camel@linux.ibm.com> References: <20251217030107.1729776-1-farman@linux.ibm.com> <8334988f-2caa-4361-b0b9-50b9f41f6d8a@linux.ibm.com> <20260114105033.23d3c699@p-imbrenda> <23154a0c6b4b9e625daa2b1bbaadc349bf3a99ed.camel@linux.ibm.com> <3d997b2645c80396c0f7c69f95fd8ec0d4784b20.camel@linux.ibm.com> Organization: IBM X-Mailer: Claws Mail 4.3.1 (GTK 3.24.49; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=NvzcssdJ c=1 sm=1 tr=0 ts=696a6ed8 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=kj9zAlcOel0A:10 a=vUbySO9Y5rIA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VnNF1IyMAAAA:8 a=IMe1qbAPzq5oirr5G9MA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-GUID: Ne3EledXv7JRNhkh_8oFldStme23Sr2H X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTE2MDEyMiBTYWx0ZWRfX/XzZdWOwjaDg 84762B7q7lGcsWLvOjxyLAH11/hC/vir3JHUy5T8eoMcxDZQA1MztFqWu/zGhRSrSq7Skkyxu6G xgVUB5Rm48uVXw3vG9sf2uEHQ6+JEnlAu5VgYVUk3fCM/jf9Fet3PKKn2Y14GE98l0o/G9buNj7 Ec1wh7RQGpq5txZc4sxzOdOk96wrz9FV4ZcX+24BpWJg377tsoGHTLTOu78eha62PBa8tV0V/49 oeS9WASWQhKOnzXqCGNueVLJorEDeAN8k8edoRZDkM5uFGebjZH8cS71176FsVTD2gPW3V522By bHzdZD5cGJcnwXKcZ7OmSygXI2Ci0lNVQfONPy464766k3PRoPmEvxRKVgtAKbJ1ITbBEwEZARi sKbNtYgw9WId2woPFNHurUPTqx2xeRF2jlRMxJFYNnFSla4lJxS/iJsBX+zQk1AKz8MEYISUQt7 rzfZ+Gtjgt0qTav4tHQ== X-Proofpoint-ORIG-GUID: Ne3EledXv7JRNhkh_8oFldStme23Sr2H X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2026-01-16_06,2026-01-15_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 suspectscore=0 clxscore=1015 adultscore=0 priorityscore=1501 spamscore=0 impostorscore=0 bulkscore=0 phishscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2512120000 definitions=main-2601160122 On Fri, 16 Jan 2026 10:45:22 -0500 Eric Farman wrote: > On Thu, 2026-01-15 at 16:17 -0500, Eric Farman wrote: > > On Wed, 2026-01-14 at 10:50 +0100, Claudio Imbrenda wrote: > > > On Mon, 05 Jan 2026 10:46:53 -0500 > > > Eric Farman wrote: > > > > > > > On Mon, 2026-01-05 at 13:41 +0100, Janosch Frank wrote: > > > > > On 12/17/25 04:01, Eric Farman wrote: > > > > > > SIE may exit because of pending host work, such as handling an interrupt, > > > > > > in which case VSIE rewinds the guest PSW such that it is transparently > > > > > > resumed (see Fixes tag). There is still one scenario where those conditions > > > > > > can you add a few words to (very briefly) explain what the scenario is? > > > > Maybe if this paragraph were rewritten this way, instead? > > > > --8<-- > > SIE may exit because of pending host work, such as handling an interrupt, > > in which case VSIE rewinds the guest PSW such that it is transparently > > resumed (see Fixes tag). Unlike those other places that return rc=0, this > > return leaves the guest PSW in place, requiring the guest to handle an > > intercept that was meant to be serviced by the host. This showed up when > > testing heavy I/O workloads, when multiple vcpus attempted to dispatch the > > same SIE block and incurred failures inserting them into the radix tree. > > -->8-- > > Spoke to Claudio offline, and he suggested the following edit to the above: > > --8<-- > SIE may exit because of pending host work, such as handling an interrupt, > in which case VSIE rewinds the guest PSW such that it is transparently > resumed (see Fixes tag). Unlike those other places that return rc=0, this > return leaves the guest PSW in place, requiring the guest to handle a > spurious intercept. This showed up when testing heavy I/O workloads, > when multiple vcpus attempted to dispatch the same SIE block and incurred > failures inserting them into the radix tree. > -->8-- with the above text: Reviewed-by: Claudio Imbrenda > > > > > @Janosch, if that ends up being okay, can you update the patch or do you want me to send a v2? > > > > > > > > > > > are not present, but that the VSIE processor returns with effectively rc=0, > > > > > > resulting in additional (and unnecessary) guest work to be performed. > > > > > > > > > > > > For this case, rewind the guest PSW as we do in the other non-error exits. > > > > > > > > > > > > Fixes: 33a729a1770b ("KVM: s390: vsie: retry SIE instruction on host intercepts") > > > > > > Signed-off-by: Eric Farman > > > > > > > > > > This is purely cosmetic to have all instances look the same, right? > > > > > > > > Nope, I can take this path with particularly high I/O loads on the system, which ends up > > > > (incorrectly) sending the intercept to the guest. > > > > > > this is a good candidate for the explanation I mentioned above :) > > > > > > > > > (the patch itself looks fine)