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zNZzGuV4mGAnOh+xl3taRqnkfcRPcYYlahkJDVAlf1d+bAQEAwQ/wzLqYuS0tNtZ2cvbGzc5w7K rD1MKAO2+FPw9hzPTyK2svLONQXiQAkcdICq9CuuSwu1t8s0W6lK1J9pfkt98L0xbZccAVEqrfT 7OSkFEGt0K3hWeZTLmuhICqIjCxME8aMvdAfMVoLUItUzg6c90LM7OupBLCRv/NijLYJzBtXduL +6+c2hUjb+pKl6Hw0k0jX9HPveOpoGSe7KQp+fEGjnEJhzMIB1QKhakk0Ns1zMJpO+k5jSQiAIw AUGM1mDrrplZwwAD3Dw3ML2I1oAfISIt3C6t3ci2/hpDksCfZbT7Ul4TyWICPEkFeKkwr6mv X-Proofpoint-ORIG-GUID: 4JO8bM7QVfueqJxqahwNab5QEO-XhEGM X-Authority-Analysis: v=2.4 cv=d731yQjE c=1 sm=1 tr=0 ts=684c2f15 b=1 cx=c_pps a=qoll8+KPOyaMroiJ2sR5sw==:117 a=qoll8+KPOyaMroiJ2sR5sw==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=kj9zAlcOel0A:10 a=6IFa9wvqVegA:10 a=GoEa3M9JfhUA:10 a=Ikd4Dj_1AAAA:8 a=yPCof4ZbAAAA:8 a=QyXUC8HyAAAA:8 a=20KFwNOVAAAA:8 a=JQGE8yVYJrqDanC0N8YA:9 a=CjuIK1q_8ugA:10 cc=ntf awl=host:13207 On Fri, Jun 13, 2025 at 03:53:58PM +0200, David Hildenbrand wrote: > On 13.06.25 15:49, Oscar Salvador wrote: > > On Fri, Jun 13, 2025 at 11:27:01AM +0200, David Hildenbrand wrote: > > > Marking PMDs that map a "normal" refcounted folios as special is > > > against our rules documented for vm_normal_page(): normal (refcounted) > > > folios shall never have the page table mapping marked as special. > > > > > > Fortunately, there are not that many pmd_special() check that can be > > > mislead, and most vm_normal_page_pmd()/vm_normal_folio_pmd() users that > > > would get this wrong right now are rather harmless: e.g., none so far > > > bases decisions whether to grab a folio reference on that decision. > > > > > > Well, and GUP-fast will fallback to GUP-slow. All in all, so far no big > > > implications as it seems. > > > > > > Getting this right will get more important as we use > > > folio_normal_page_pmd() in more places. > > > > > > Fix it by teaching insert_pfn_pmd() to properly handle folios and > > > pfns -- moving refcount/mapcount/etc handling in there, renaming it to > > > insert_pmd(), and distinguishing between both cases using a new simple > > > "struct folio_or_pfn" structure. > > > > > > Use folio_mk_pmd() to create a pmd for a folio cleanly. > > > > > > Fixes: 6c88f72691f8 ("mm/huge_memory: add vmf_insert_folio_pmd()") > > > Reviewed-by: Jason Gunthorpe > > > Reviewed-by: Lorenzo Stoakes > > > Reviewed-by: Dan Williams > > > Tested-by: Dan Williams > > > Signed-off-by: David Hildenbrand > > > > Altough we have it quite well explained here in the changelog, maybe > > having a little comment in insert_pmd() noting why pmds mapping normal > > folios cannot be marked special would be nice. > > Well, I don't think we should be replicating that all over the place. The > big comment above vm_normal_page() is currently our source of truth (which I > will teak soon further). Suggestion: "Kinda self-explanatory (special means don't touch) unless you use museum piece hardware OR IF YOU ARE XEN!" ;) > > Thanks! > > -- > Cheers, > > David / dhildenb >