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Thu, 15 Jan 2026 21:17:23 +0000 (GMT) Message-ID: <23154a0c6b4b9e625daa2b1bbaadc349bf3a99ed.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: Thu, 15 Jan 2026 16:17:23 -0500 In-Reply-To: <20260114105033.23d3c699@p-imbrenda> References: <20251217030107.1729776-1-farman@linux.ibm.com> <8334988f-2caa-4361-b0b9-50b9f41f6d8a@linux.ibm.com> <20260114105033.23d3c699@p-imbrenda> 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-Spam-Details-Enc: AW1haW4tMjYwMTE1MDE2MyBTYWx0ZWRfX49NOTknypqdW xYwy9zqF2mfb0GnrFK7Vz+XCabo9evcuRYPCY5qN3Mb7K+rVi32BTBI9Vb1LUKXwd8xdtLdpiUt TbJFYBYi/Y6wPj6ZOI0/8NBmJMT6aTKr6Lh5YfocJnD+v084xmGBj0YX7BJ8YVrNwPYVOEid/0f ZkOMciMVZNFFjnBlHGiSvWzqgx/oQfY8yUXXSrRFvZSiSOURk/ETj4uEhwNnZzmSMWB5XT4GoDz BeGxdiZQm1IweiU7cYZ2ler5MMlTsFWTx43PkMSrmcHPY0gezIAtUi4e2mBMNfqzEvmd0Aq3Y09 bYoR+Dkg/wmYWYlcRfuq3y0cWtaD81SLZ2L13ankL3OuReMRVorDQnwMO6K7u/DBXT1hR/ztYvl KwpwfOCoJgQwgfRfaXwYC8HYtFO3xOSRZkR2uiragU6s0VjTlelp7ev97Ne/cLyupGaEQnhrQlp 1l/kDMEM4P7cR3JHyLA== X-Proofpoint-ORIG-GUID: FKUeb_6zItlZh6Jis7u3sCjhi9KrFiDj X-Proofpoint-GUID: FKUeb_6zItlZh6Jis7u3sCjhi9KrFiDj X-Authority-Analysis: v=2.4 cv=U4afzOru c=1 sm=1 tr=0 ts=69695967 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=vUbySO9Y5rIA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VnNF1IyMAAAA:8 a=8mLeQlhjTlvVVX_YL8kA:9 a=NqO74GWdXPXpGKcKHaDJD/ajO6k=:19 a=QEXdDO2ut3YA:10 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=2026-01-15_06,2026-01-15_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 clxscore=1015 priorityscore=1501 lowpriorityscore=0 adultscore=0 malwarescore=0 bulkscore=0 phishscore=0 suspectscore=0 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2512120000 definitions=main-2601150163 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 inte= rrupt, > > > > in which case VSIE rewinds the guest PSW such that it is transparen= tly > > > > resumed (see Fixes tag). There is still one scenario where those co= nditions >=20 > 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=3D0, 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-- @Janosch, if that ends up being okay, can you update the patch or do you wa= nt me to send a v2? >=20 > > > > are not present, but that the VSIE processor returns with effective= ly rc=3D0, > > > > resulting in additional (and unnecessary) guest work to be performe= d. > > > >=20 > > > > For this case, rewind the guest PSW as we do in the other non-error= exits. > > > >=20 > > > > Fixes: 33a729a1770b ("KVM: s390: vsie: retry SIE instruction on hos= t 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 syst= em, 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)