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boundary="Apple-Mail=_2835EB76-12D0-4946-979A-7D70876143CA"; protocol="application/pkcs7-signature"; micalg=sha-256 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-OriginatorOrg: akamai.com X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-19_01,2026-03-17_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 mlxscore=0 malwarescore=0 adultscore=0 lowpriorityscore=0 mlxlogscore=999 suspectscore=0 spamscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2603050001 definitions=main-2603190067 X-Authority-Analysis: v=2.4 cv=Q+LiJY2a c=1 sm=1 tr=0 ts=69bbb5aa cx=c_pps a=WPLAOKU3JHlOa4eSsQmUFQ==:117 a=WPLAOKU3JHlOa4eSsQmUFQ==:17 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=xqWC_Br6kY4A:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=Ifg-1AOnLHOf1gn6spyb:22 a=d4nn1RXdvEacMIURMw2s:22 a=r1p2_3pzAAAA:8 a=Tf3fbeekh0F0YBeSp_AA:9 a=QEXdDO2ut3YA:10 a=aUQEjLJJORIxqg3IqZUA:9 a=ZVk8-NSrHBgA:10 a=30ssDGKg3p0A:10 a=r_pkcD-q9-ctt7trBg_g:22 X-Proofpoint-GUID: Z2kp2isFyYPxrle51zwN_HmiHN7XDDi7 X-Proofpoint-ORIG-GUID: Z2kp2isFyYPxrle51zwN_HmiHN7XDDi7 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzE5MDA2NyBTYWx0ZWRfX1/sBO1K4o1K+ jv/pRxw/6uKFSsOzEO/IoMWknxXYYzPqcXvOtbB+lR4U6iGuzltQvX+TzUYzkiLHXX/Ycgb2dbI uNOyfJu9nR3gP2frHk5Jsvv1AMYl3gEFfNrOjl3dBFYG67GlT2cT8b3BDetcE5PhSZbZRXkjMgs +vA9tzPbAISW1rRopeC5LH5FKxliqbhR7TXpPaYWmFfkK2/Pqp1aWHzmtEhaSuOyp8jltqKdNfW h2eLANuZPN3/AMytvWAkdoOogf/hOXbP8XVhsKLE4O+aDeO+cR7WAiQQz0fbAZM+g1EADQ5De8G TPe0H+KabmeEWxNEzzMAK+gzCUG7mY9xQVHdLhpScuCkFoTF/tu3G1ZKCB2Noy0CI0YkFM6k4HV PVonogRpywD3szyLsGs6NDQYByUJnNPDnof3vFwzO14ZmgT4avHNtkNXSXDEjoXZC1uoqTh/+44 ScJGDMVpyZQABWo1FVg== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-19_01,2026-03-17_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 suspectscore=0 impostorscore=0 spamscore=0 adultscore=0 clxscore=1011 phishscore=0 lowpriorityscore=0 bulkscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603130000 definitions=main-2603190067 --Apple-Mail=_2835EB76-12D0-4946-979A-7D70876143CA Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 > On Mar 18, 2026, at 10:22=E2=80=AFPM, Alex Williamson = wrote: >=20 > [=E2=80=A6] >=20 >> + /* >> + * follow_pfnmap_start() returns -EINVAL for >> + * invalid parameters and non-present entries. >> + * If that happens here after a successful >> + * fixup_user_fault(), it is likely that the >> + * pfnmap has been zapped. Retry instead of >> + * failing. >> + */ >=20 > It's a little stronger than that, right? We're betting that the only > remaining non-zero return is due to a race and we can introduce what > appears to be potential for an infinite loop here because -EAGAIN will > get kicked out to redo the vma_lookup() and fixup_user_fault() should > return a genuine error if we're completely in the weeds. Should we > make this a little stronger and more specific? Thanks, I=E2=80=99d say that the best case would be to have = follow_pfnmap_start() return -EINVAL or -ENOENT w.r.t. which of the two return values it is. But then again, we could theoretically run into an infinite loop I guess - as the = zap and faulting could run in lockstep (the race window is extremely small though). We could make the retry above bounded, and bubble up a -EBUSY such that users of the ioctl can decide to retry instead of fail? David, you mentioned that gup already has retry logic that we don=E2=80=99= t have with follow_fault_pfn() -> follow_pfnmap_start(). Would we potentially = run into an infinite loop with this change? I see that the same pattern also appears in: - virt/kvm/kvm_main.c:hva_to_pfn_remapped() - s390/pci/pci_mmio.c:s390_pci_mmio_write() And other users of the function are: - drivers/virt/acrn/mm.c:acrn_vm_ram_map() - mm/memory.c:generic_access_phys() Maybe I can better draft in this patch with adding an -ENOENT return to follow_pfnmap_start() and in the same patchset add retrying logic where necessary (on first sight, kvm and vfio)? >=20 > Alex >=20 >> ret =3D follow_pfnmap_start(&args); >> if (ret) >> - return ret; >> + return -EAGAIN; >> } >>=20 >> if (write_fault && !args.writable) { >>=20 >> --- >> base-commit: 96ca4caf9066f5ebd35b561a521af588a8eb0215 >> change-id: 20260317-retry-pin-on-reclaimed-pud-dfb9e26eb8cf >>=20 >> Best regards, >=20 --Apple-Mail=_2835EB76-12D0-4946-979A-7D70876143CA Content-Disposition: attachment; filename="smime.p7s" Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 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