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X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: m44HcOscNG+VUFgW6frrQLVuVgqnfoKsDO0teCMMJnXuP3wG12DJlxDHCkeKIck4VFEbcnDS+bCYxUTyzMeG7w== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY8PR10MB6729 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.1.7,FMLib:17.12.80.40 definitions=2025-07-08_03,2025-07-07_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 bulkscore=0 malwarescore=0 mlxlogscore=999 spamscore=0 phishscore=0 mlxscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2505160000 definitions=main-2507080083 X-Proofpoint-GUID: LJqVrHZ0gJ731aVd5EgM6qv7qEFMbcWy X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNzA4MDA4MyBTYWx0ZWRfX72ZmWZKDFGnY Z8/5FXH9R7O4+4tIctKzjZat33ieeQCsGav1np9ZJUkIcmRlY6lVkNbyMv5ZfxfTT5IZjyglqRr +2W7S/BrU+MigabwRwxfB9BAm7aSvjNoLSLEtX8t6Ty5KMvvGMRX7GIxT9ZpQVnSWCzkSstZLqN +6zqQ2zut+5/hygFhcZ8IvlZnarTNTeiB2/B+TwuR1rIYWXm5gWDMzUlXbCHSi4EEIce7JOCFCz ueUG/fTKSO8qWxe8NoLlk/w4gaBKTwpl3gIPY/1K4lH58a2KVEqd92nu/GNXPQVdFx5iq8c7JfN yEJV17JKqDc1tRhoXWV4i+MH7QJ2VGsrzYYrbNDNIUBFHNXWF0dkNMcHE3bxQ5cMPoPvH8uRKSz Qu9AFl+Gt2mIV8uQ43nHd1aZ261QU40/3J5QAoW13KEfS+2Kp4w2SQLvwtGtP+OrcQVlDFZJ X-Authority-Analysis: v=2.4 cv=Lq2Symdc c=1 sm=1 tr=0 ts=686cee29 cx=c_pps a=XiAAW1AwiKB2Y8Wsi+sD2Q==:117 a=XiAAW1AwiKB2Y8Wsi+sD2Q==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=I5r0CxplrSDLCy34:21 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=Wb1JkmetP80A:10 a=GoEa3M9JfhUA:10 a=pfleYRJ_qRmfgFO1rC8A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: LJqVrHZ0gJ731aVd5EgM6qv7qEFMbcWy On 07/07/2025 15:18, Christoph Hellwig wrote: > Hi all, > > I'm a bit lost on what to do about the sad state of NVMe atomic writes. > > As a short reminder the main issues are: > > 1) there is no flag on a command to request atomic (aka non-torn) > behavior, instead writes adhering to the atomicy requirements will > never be torn, and writes not adhering them can be torn any time. > This differs from SCSI where atomic writes have to be be explicitly > requested and fail when they can't be satisfied > 2) the original way to indicate the main atomicy limit is the AWUPF > field, which is in Identify Controller, but specified in logical > blocks which only exist at a namespace layer. This a) lead to > various problems because the limit is a mess when namespace have > different logical block sizes, and it b) also causes additional > issues because NVMe allows it to be different for different > controllers in the same subsystem. > > Commit 8695f060a029 added some sanity checks to deal with issue 2b, > but we kept running into more issues with it. Partially because > the check wasn't quite correct, but also because we've gotten > reports of controllers that change the AWUPF value when reformatting > namespaces to deal with issue 2a. > > And I'm a bit lost on what to do here. > > We could: > > I. revert the check and the subsequent fixup. If you really want > to use the nvme atomics you already better pray a lot anyway > due to issue 1) > II. limit the check to multi-controller subsystems > III. don't allow atomics on controllers that only report AWUPF and > limit support to controllers that support that more sanely > defined NAWUPF This would help avoid the ambiguity in whether NABSPF is valid if nsfeat bit 1 is unset. However, it would be nice to have an idea of how many/percentage of products it would affect today. FWIW, I only have 1x SSD which supports atomics, and it does set that bit. I suppose we could quirk known "good" HW which relies on AWUPF (to enable atomics), but that is very far from a nice approach. > > I guess for 6.16 we are limited to I. to bring us back to the previous > state, but I have a really bad gut feeling about it given the really > bad spec language and a lot of low quality NVMe implementations we're > seeing these days. > not the