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Fri, 16 Jan 2026 15:45:23 +0000 (GMT) Message-ID: <3d997b2645c80396c0f7c69f95fd8ec0d4784b20.camel@linux.ibm.com> Subject: Re: [PATCH] KVM: s390: vsie: retry SIE when unable to get vsie_page From: Eric Farman To: Claudio Imbrenda Cc: Janosch Frank , Christian Borntraeger , David Hildenbrand , Christoph Schlameuss , kvm@vger.kernel.org, linux-s390@vger.kernel.org Date: Fri, 16 Jan 2026 10:45:22 -0500 In-Reply-To: <23154a0c6b4b9e625daa2b1bbaadc349bf3a99ed.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> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.2 (3.58.2-1.fc43) Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: dDH18FFknHcJR0GCRpPV3nK2hie-m5J4 X-Proofpoint-ORIG-GUID: dDH18FFknHcJR0GCRpPV3nK2hie-m5J4 X-Authority-Analysis: v=2.4 cv=TrvrRTXh c=1 sm=1 tr=0 ts=696a5d16 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=vUbySO9Y5rIA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VnNF1IyMAAAA:8 a=R0r9cqHsO0Xgfa1iM50A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTE2MDEwOSBTYWx0ZWRfX+CLOBUBHEfVh W/pmCbNpapgeZBOYQw5FcyiNJbxrt8gD5yplIGjIgl7iY1zeDKt6sZE82GRiCgp79PBwF6UjqKI WTdY3r/lELOFlXUVZdG+zO4HY0Su+ZApE51UEkDr9A8pbohYqIWEcZwHyew9s727Bg+E8HD+PLI YRBcPwE61M5UvUzjJ/0jKqIMDKcaK684XEE034OWHv32EY89ZiD7N6WwOrMsg7HVNokTqI0epR5 5+JEk5uNDpmNPGzYhMiiaOfKpHH527oUM0FxowDsk9eSIbjJXl39uglbEh2r7oGpi7AqN2Re1Sq mjdSUmOSdj6qKv4yYIgC/SE+s5SrdE+uwCFTqUJ+5exx2lLiR8E+H+GEm6N7fEOnvCjuHIDnTZa ACIjE3azeni3JjZV+oDK9LTs1t7QWv5yyCwAmcmDv7mWWCRZTD/4C+CfWsJ9ho6Skwrr0UCcNyW uAiVdJ1N45pPj/PWujg== 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 spamscore=0 priorityscore=1501 lowpriorityscore=0 phishscore=0 clxscore=1015 bulkscore=0 impostorscore=0 malwarescore=0 suspectscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2512120000 definitions=main-2601160109 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: > >=20 > > > On Mon, 2026-01-05 at 13:41 +0100, Janosch Frank wrote: > > > > On 12/17/25 04:01, Eric Farman wrote: =20 > > > > > SIE may exit because of pending host work, such as handling an in= terrupt, > > > > > in which case VSIE rewinds the guest PSW such that it is transpar= ently > > > > > resumed (see Fixes tag). There is still one scenario where those = conditions > >=20 > > can you add a few words to (very briefly) explain what the scenario is? >=20 > Maybe if this paragraph were rewritten this way, instead? >=20 > --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=3D0, th= is > 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 th= e > 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=3D0, 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-- >=20 > @Janosch, if that ends up being okay, can you update the patch or do you = want me to send a v2? >=20 > >=20 > > > > > are not present, but that the VSIE processor returns with effecti= vely rc=3D0, > > > > > resulting in additional (and unnecessary) guest work to be perfor= med. > > > > >=20 > > > > > For this case, rewind the guest PSW as we do in the other non-err= or exits. > > > > >=20 > > > > > Fixes: 33a729a1770b ("KVM: s390: vsie: retry SIE instruction on h= ost intercepts") > > > > > Signed-off-by: Eric Farman =20 > > > >=20 > > > > This is purely cosmetic to have all instances look the same, right?= =20 > > >=20 > > > Nope, I can take this path with particularly high I/O loads on the sy= stem, which ends up > > > (incorrectly) sending the intercept to the guest. > >=20 > > this is a good candidate for the explanation I mentioned above :) > >=20 > >=20 > > (the patch itself looks fine)