On 22.10.24 11:00, David Hildenbrand wrote:
From: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> Patch series "mm: don't install PMD mappings when THPs are disabled by the hw/process/vma". During testing, it was found that we can get PMD mappings in processes where THP (and more precisely, PMD mappings) are supposed to be disabled. While it works as expected for anon+shmem, the pagecache is the problematic bit. For s390 KVM this currently means that a VM backed by a file located on filesystem with large folio support can crash when KVM tries accessing the problematic page, because the readahead logic might decide to use a PMD-sized THP and faulting it into the page tables will install a PMD mapping, something that s390 KVM cannot tolerate. This might also be a problem with HW that does not support PMD mappings, but I did not try reproducing it. Fix it by respecting the ways to disable THPs when deciding whether we can install a PMD mapping. khugepaged should already be taking care of not collapsing if THPs are effectively disabled for the hw/process/vma. This patch (of 2): Add vma_thp_disabled() and thp_disabled_by_hw() helpers to be shared by shmem_allowable_huge_orders() and __thp_vma_allowable_orders(). [david@xxxxxxxxxx: rename to vma_thp_disabled(), split out thp_disabled_by_hw() ] Link: https://lkml.kernel.org/r/20241011102445.934409-2-david@xxxxxxxxxx Fixes: 793917d997df ("mm/readahead: Add large folio readahead") Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Reported-by: Leo Fu <bfu@xxxxxxxxxx> Tested-by: Thomas Huth <thuth@xxxxxxxxxx> Reviewed-by: Ryan Roberts <ryan.roberts@xxxxxxx> Cc: Boqiao Fu <bfu@xxxxxxxxxx> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx> Cc: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Janosch Frank <frankja@xxxxxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> (cherry picked from commit 963756aac1f011d904ddd9548ae82286d3a91f96) Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> --- Only contextual differences in shmem_allowable_huge_orders(). Note that this patch is required to backport the fix 2b0f922323ccfa76219bcaacd35cd50aeaa13592, which can be cleanly cherry picked on top.
ARG my backporting skills (or rather patch sending skills) are not strong today. This is the 6.11.y variant. Please ignore this mail ... :(
-- Cheers, David / dhildenb
