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charset=utf-8 > On Mar 11, 2026, at 11:45=E2=80=AFAM, David Hildenbrand (Arm) = wrote: >=20 > The code in follow_fault_pfn() should likely be updated to handle more > than one attempt. That's also what GUP does. >=20 > Likely, follow_fault_pfn() was never taught about PFNMAP mappings that > can be faulted+zapped (in the past they were always static). >=20 > If you turn that into a (possibly) endless loop, does the problem go = away? Yep, was just trying that - with this change the problem goes away: --- a/drivers/vfio/vfio_iommu_type1.c +++ b/drivers/vfio/vfio_iommu_type1.c @@ -532,7 +532,7 @@ static int follow_fault_pfn(struct vm_area_struct = *vma, struct mm_struct *mm, ret =3D follow_pfnmap_start(&args); if (ret) - return ret; + return -EAGAIN; } if (write_fault && !args.writable) =E2=80=94 I=E2=80=99ll propose that with the VFIO folks when I get the patch for = mm/pagewalk.c ready and will refer to that patch, or would it be better to propose two commits under the = same cover letter? I can have a look at follow_fault_pfn but this problem is my first time = diving into linux mm so that will probably take a while (and some reading up on my end). >=20 > --=20 > Cheers, >=20 > David --Apple-Mail=_02321BE6-5527-464E-950B-8A59BC1BF43E Content-Disposition: attachment; filename="smime.p7s" Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCCcow ggShMIIESKADAgECAhMxAAAAIa0XYPGypwcKAAAAAAAhMAoGCCqGSM49BAMCMD8xITAfBgNVBAoT GEFrYW1haSBUZWNobm9sb2dpZXMgSW5jLjEaMBgGA1UEAxMRQWthbWFpQ29ycFJvb3QtRzEwHhcN MjQxMTIxMTgzNzUyWhcNMzQxMTIxMTg0NzUyWjA8MSEwHwYDVQQKExhBa2FtYWkgVGVjaG5vbG9n aWVzIEluYy4xFzAVBgNVBAMTDkFrYW1haUNsaWVudENBMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcD QgAEjkdeMHsSTytADJ7eJ+O+5mpBfm9hVC6Cg9Wf+ER8HXid3E68IHjcCTNFSiezqYclAnIalS1I cl6hRFZiacQkd6OCAyQwggMgMBIGCSsGAQQBgjcVAQQFAgMBAAEwIwYJKwYBBAGCNxUCBBYEFOa0 4dX2BYnqjkbEVEwLgf7BQJ7ZMB0GA1UdDgQWBBS2N+ieDVUAjPmykf1ahsljEXmtXDCBrwYDVR0g BIGnMIGkMIGhBgsqAwSPTgEJCQgBATCBkTBYBggrBgEFBQcCAjBMHkoAQQBrAGEAbQBhAGkAIABD AGUAcgB0AGkAZgBpAGMAYQB0AGUAIABQAHIAYQBjAHQAaQBjAGUAIABTAHQAYQB0AGUAbQBlAG4A dDA1BggrBgEFBQcCARYpaHR0cDovL2FrYW1haWNybC5ha2FtYWkuY29tL0FrYW1haUNQUy5wZGYw bAYDVR0lBGUwYwYIKwYBBQUHAwIGCCsGAQUFBwMEBgorBgEEAYI3FAICBgorBgEEAYI3CgMEBgor BgEEAYI3CgMMBggrBgEFBQcDBwYIKwYBBQUHAwkGCSsGAQQBgjcVBQYKKwYBBAGCNxQCATAZBgkr BgEEAYI3FAIEDB4KAFMAdQBiAEMAQTALBgNVHQ8EBAMCAYYwDwYDVR0TAQH/BAUwAwEB/zAfBgNV HSMEGDAWgBStAYfq3FmusRM5lU0PV6Akhot7vTCBgAYDVR0fBHkwdzB1oHOgcYYxaHR0cDovL2Fr YW1haWNybC5ha2FtYWkuY29tL0FrYW1haUNvcnBSb290LUcxLmNybIY8aHR0cDovL2FrYW1haWNy bC5kZncwMS5jb3JwLmFrYW1haS5jb20vQWthbWFpQ29ycFJvb3QtRzEuY3JsMIHIBggrBgEFBQcB AQSBuzCBuDA9BggrBgEFBQcwAoYxaHR0cDovL2FrYW1haWNybC5ha2FtYWkuY29tL0FrYW1haUNv cnBSb290LUcxLmNydDBIBggrBgEFBQcwAoY8aHR0cDovL2FrYW1haWNybC5kZncwMS5jb3JwLmFr YW1haS5jb20vQWthbWFpQ29ycFJvb3QtRzEuY3J0MC0GCCsGAQUFBzABhiFodHRwOi8vYWthbWFp b2NzcC5ha2FtYWkuY29tL29jc3AwCgYIKoZIzj0EAwIDRwAwRAIgaUoJ7eBk/qNcBVTJW5NC4NsO 6j4/6zQoKeKgOpeiXQUCIGkbSN83n1mMURZIK92KFRtn2X1nrZ7rcNuAQD5bvH1bMIIFITCCBMig AwIBAgITFwALOJfLRtbGzZc1dwABAAs4lzAKBggqhkjOPQQDAjA8MSEwHwYDVQQKExhBa2FtYWkg VGVjaG5vbG9naWVzIEluYy4xFzAVBgNVBAMTDkFrYW1haUNsaWVudENBMB4XDTI1MDgyODA3NTYy OVoXDTI3MDgyODA3NTYyOVowTjEZMBcGA1UECxMQTWFjQm9vayBQcm8tNDZZVDEPMA0GA1UEAxMG bWJvb25lMSAwHgYJKoZIhvcNAQkBFhFtYm9vbmVAYWthbWFpLmNvbTCCASIwDQYJKoZIhvcNAQEB BQADggEPADCCAQoCggEBAOX+npfSrX/rwhOySq6aejQMUVslPFpNvXdEnmMlnEjR95gq0Ygp+wQc Sde+JGBpGHsPMzHT1Nd3V1acm4cW1WB1aRqJOMfSLifg6SLkq2EM9WsftEiA1G4BT4UP0PFZY2Os 6TXvebAuVg6LwhB417rEJ2kuS/DKpiG8trAVDR6Uy9vbSMBp6iIewBc9r0CjW8l1zgRr+uQpXEUP mF2BV0l3Qo5r0nhPqTWR9oAX4/oTqnhbEhQ3tOFYTjzO1K9DdzX8mVggVSZz/M0v0gtkZVvO4B1t 3Sh+1lla5eMY4hlVHW1/FKqMe4EMXmDH7goTEuXPpelJiNRdBh7ud7xNNFUCAwEAAaOCAsowggLG MAsGA1UdDwQEAwIHgDApBgNVHSUEIjAgBggrBgEFBQcDAgYIKwYBBQUHAwQGCisGAQQBgjcKAwQw HQYDVR0OBBYEFO0y/xWMpkyOUMuNKmuzNtjXpdtRMEQGA1UdEQQ9MDugJgYKKwYBBAGCNxQCA6AY DBZtYm9vbmVAY29ycC5ha2FtYWkuY29tgRFtYm9vbmVAYWthbWFpLmNvbTAfBgNVHSMEGDAWgBS2 N+ieDVUAjPmykf1ahsljEXmtXDCBgAYDVR0fBHkwdzB1oHOgcYYxaHR0cDovL2FrYW1haWNybC5h a2FtYWkuY29tL0FrYW1haUNsaWVudENBKDEpLmNybIY8aHR0cDovL2FrYW1haWNybC5kZncwMS5j b3JwLmFrYW1haS5jb20vQWthbWFpQ2xpZW50Q0EoMSkuY3JsMIHIBggrBgEFBQcBAQSBuzCBuDA9 BggrBgEFBQcwAoYxaHR0cDovL2FrYW1haWNybC5ha2FtYWkuY29tL0FrYW1haUNsaWVudENBKDEp LmNydDBIBggrBgEFBQcwAoY8aHR0cDovL2FrYW1haWNybC5kZncwMS5jb3JwLmFrYW1haS5jb20v QWthbWFpQ2xpZW50Q0EoMSkuY3J0MC0GCCsGAQUFBzABhiFodHRwOi8vYWthbWFpb2NzcC5ha2Ft YWkuY29tL29jc3AwOwYJKwYBBAGCNxUHBC4wLAYkKwYBBAGCNxUIgs7lOoe41C2BhYsHouMhhtIP gUmFpcMQmtV/AgFkAgFTMDUGCSsGAQQBgjcVCgQoMCYwCgYIKwYBBQUHAwIwCgYIKwYBBQUHAwQw DAYKKwYBBAGCNwoDBDBEBgkqhkiG9w0BCQ8ENzA1MA4GCCqGSIb3DQMCAgIAgDAOBggqhkiG9w0D BAICAIAwBwYFKw4DAgcwCgYIKoZIhvcNAwcwCgYIKoZIzj0EAwIDRwAwRAIgD5UL4MI1RXeg64RR kifZAeItCnkZ4ecrqSEGpLcXV+ICIAdB9vZdM1WGxtag0rlqG0j0FBrCWixC0cdHNpFrqNx/MYIB 6TCCAeUCAQEwUzA8MSEwHwYDVQQKExhBa2FtYWkgVGVjaG5vbG9naWVzIEluYy4xFzAVBgNVBAMT DkFrYW1haUNsaWVudENBAhMXAAs4l8tG1sbNlzV3AAEACziXMA0GCWCGSAFlAwQCAQUAoGkwGAYJ KoZIhvcNAQkDMQsGCSqGSIb3DQEHATAcBgkqhkiG9w0BCQUxDxcNMjYwMzExMTExNDQyWjAvBgkq hkiG9w0BCQQxIgQgCs6OVTDg0SQYY71+hATZmIx5zV2be8G0VF6ckCOqjtgwDQYJKoZIhvcNAQEL BQAEggEAzkMinc3iWGeflxyrSOuKUAN7avikpVMkVm3VtBy63Q4hjSw9QzqZfcXZ5ZlrB1ZNnwu6 PHbITBpYWKCqsATE3LfLk9GyVjylCQScJT52IMSqmSeOGD8R9P9bdmvPrZHOWMpX1XBUFZBnO+gT tq9HxKTM4QkdwzSVLpanrPHS3fiAO9iUetMN1ieTOQHLu1LunaM87M/4Gnl/YcWHklAQ8S3CXebk 5D38K/URoyGOE2VvDv3UzWZtCZl2hVMSj2o6uJhBPfURsuqckyXb3/qEn3huVi+JOvDeGDeV6+3j UayTHtGxxRnprCPZESG3Z3B3L9PfsIDx8K63P/JXUcP5pQAAAAAAAA== --Apple-Mail=_02321BE6-5527-464E-950B-8A59BC1BF43E--