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charset=utf-8 > On Mar 18, 2026, at 1:55=E2=80=AFPM, Lorenzo Stoakes (Oracle) = wrote: >=20 >> [=E2=80=A6] >=20 > So IOW, the PUD entry is split, then refaulted back to a PUD leaf = entry > again? As far as I understand indeed, although the usage and faulting of huge pfnmaps does not feel intuitive to me yet. Empirically, yes, observing = this when follow_fault_pfn() in drivers/vfio/vfio_iommu_type1.c is running=20 concurrently with walk_pud_range(). I have another patch sent up to that list because this fix causes follow_fault_pfn() to return -EINVAL = [1]. >> [=E2=80=A6]=20 >=20 > I think it mirrors the retry logic in walk_pte_range() more closely = right? > Because there it's: >=20 > if (!pte) > walk->action =3D ACTION_AGAIN; > return err; >=20 > I.e. let the parent handle the PTE not being got by = pte_offset_map_lock(), > and you draw a comparison to this in the comment in walk_pmd_range(). I=E2=80=99d personally say that the main logic introduced is = walk_pud_range() retrying when walk_pmd_range() fails. We=E2=80=99re also splitting the PUD in = walk_pud_range() and=20 descending. But yeah, retry logic mirrors walk_pmd_range(), deciding = that we need to retry mirrors walk_pte_range(). >=20 >>=20 >> Fixes: a00cc7d9dd93 ("mm, x86: add support for PUD-sized transparent = hugepages") >=20 > Yikes, really? :) This is from 2017, I'm a little surprised we didn't = hit > this bug until now. >=20 > Has something changed more recently that made it more likely to hit? = Or is > it one of those 'needed people to have more RAM first' or bigger PCI = BAR's? Yeah, frankly, this is the first patch where I could find the splitting = being introduced. It might be more correct to refer to the introduction of 1G huge_pfnmaps? >=20 >> Cc: stable@vger.kernel.org >> Co-developed-by: David Hildenbrand (Arm) >> Signed-off-by: David Hildenbrand (Arm) >> Signed-off-by: Max Boone >=20 > Only nits here, the logic LGTM, so: I=E2=80=99ll write up a PATCH v2 later today. >=20 > [=E2=80=A6] --Apple-Mail=_B94DFD7E-C0EE-4800-BB88-4B5486579E43 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 KoZIhvcNAQkDMQsGCSqGSIb3DQEHATAcBgkqhkiG9w0BCQUxDxcNMjYwMzE4MTMwODIxWjAvBgkq hkiG9w0BCQQxIgQgC2sf1ds164KoW2XEGvA8X/UU1wcheHgI+RkqZKvr2hUwDQYJKoZIhvcNAQEL BQAEggEAEDHvutozO8JE+6lItYkKrMQf/77EGrtNZudgEuQXJmBZcgx5BTFAOYGInYRMlAh9JF+j QUCnOJ10/m1ldzEZvH4657ORwC7M7ff2yKYhKzoinJJIksCn95a1nxT+MXk8hIxgBizB6QyaFmRD QYNGI06Jl6X42P91l9NbzpTchQGl7MCcFzCZPIX3Uq1HlklUwDMdnyVPVtQonSd+jflOZN2aDlRy sQjAcDY84ktgytLVTyvzh9hIM0Ceq4d26rkfyraMrH3g7JdJhrSvukAW8/iPhfXqk1d/MHk5ny5O 6QXCLK/CH1PxMXOnRiybGu9/hOfBo0xghPtWz77JF0PWeQAAAAAAAA== --Apple-Mail=_B94DFD7E-C0EE-4800-BB88-4B5486579E43--