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Howlett , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, yosry@kernel.org, qi.zheng@linux.dev, luizcap@redhat.com, kernel-team@meta.com, Usama Arif Subject: [PATCH v8 18/30] mm/hmm: fault PMD swap entries on demand Date: Fri, 2 Oct 2026 02:52:32 -0700 Message-ID: <20261002095503.3585565-19-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261002095503.3585565-1-usama.arif@linux.dev> References: <20261002095503.3585565-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: 386p8mod3kzm53pd4kbiyqzsagnpajow X-Rspamd-Queue-Id: 68E0DC0003 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1790935024-521312 X-HE-Meta: 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 1B4I9vWg dinETKVlDg6R4ejn0P/TYMgxoEOGOqR4ZDqupDjgDasHMgJhiGBGKQet5bicj2r39IEjDq5IJQy3ONfzZwzJQfUDc64DNqMZpPDsox1UifmCt8HdqbDFDJHwY4Iz8MfcFjW1zAs/tLClGv7Qp/sQsZw2UezYeopWJJCtrdOBc26gnIyii7zrQVGeRuipHjWACq5zlQcntoImt5EnIlsOxxMmcgIg0xiHGz6C/ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: hmm_vma_handle_absent_pmd() reports anything non-present that is not device-private as HMM_PFN_ERROR, so a swapped-out THP would look like a permanent failure rather than memory that needs paging in. Treat it like a PTE swap entry: record the fault when one was asked for, and otherwise report the range as non-resident with no flags, which is what hmm_vma_handle_pte() already does in snapshot mode. Signed-off-by: Usama Arif --- mm/hmm.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/mm/hmm.c b/mm/hmm.c index 2f1e98c6b6440..95575ac378888 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -377,12 +377,21 @@ static int hmm_vma_handle_absent_pmd(struct mm_walk *walk, unsigned long start, required_fault = hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0); if (required_fault) { - if (softleaf_is_device_private(entry)) + if (softleaf_is_device_private(entry) || + softleaf_is_swap(entry)) return hmm_record_fault(addr, end, required_fault, walk); else return -EFAULT; } + /* + * A swapped-out THP is not resident. Report it as not-valid, + * matching what hmm_vma_handle_pte() does for a PTE swap entry when + * no fault was requested. + */ + if (softleaf_is_swap(entry)) + return hmm_pfns_fill(start, end, range, 0); + return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR); } #else -- 2.53.0-Meta