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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: [RESEND v7 17/29] mm/hmm: fault PMD swap entries on demand Date: Mon, 14 Sep 2026 05:28:07 -0700 Message-ID: <20260914122950.3283997-18-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260914122950.3283997-1-usama.arif@linux.dev> References: <20260914122950.3283997-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: AD1A310000D X-Stat-Signature: 6rk5x341ag1kd695qcq73s98ou4jurf3 X-HE-Tag: 1789389104-221084 X-HE-Meta: U2FsdGVkX1/ZjQONNCPU+jndjj1zKb2f54tKcnUMkwJ381sB5BePZ3oQ4L8wl43hRsPDDV3WyAr+EkIOQHKVCia1pU3XRbn2DPYs77Pxe04dlqAkieF/yrA0ISqwiFr0bw6a1LKVqIq82xA2ec+WLO4efF1ob8COySZE21suXiE8LsKq8a4edr1vx2BPrilUwp4vRLI9azI1bVWB/kOEUsUax8dbPFrtW+pkGRdEnv/cTdlUGnKwb6sfG9A9AK2h2Q0Uq6U2Y6/95mUg1Tk0NRQnJMPl5f9y1hyJnzF592iYMHxS5wJf3Zdxbu4q/nfCMsFW6UzB7OzN1xV9ykNzMFziwXnvTEjMNtl49htNBMRXNOGBETCZmVE6eS8rxsVsGh7KiR8ypxliNLtbOYBi/7Pan3I9h1+bbeMPYoeDE3Mcmld1pIVQl8iQL2Z3axnGKag5U6kw/f25dD9Mup4FD+s5xdZ1V7BMIm2Al7a5ywZcC+ytI0IAblNPKGwJS5r5HgWd1rKnCeBM3M6slOdgFNmeyTaUSh6IBu1mqYZMUE3iIzxa+i1029g6t3XmR0ex/9p3p/Y3Y9dozoPlhkB2+3w8Oqlw0B1r8txQ+WBeHEVL7kgH0JhAMhvvChTaMynXtMsdUnCuEk0NC9KnGnkQt3dcNtqrq7hd53iYzCOf1eptYtOIdHxqgf8h0QKH9x4TnA5McQqLtBl2bbVEmuRg/ItxFmmgkWB0+M8TwQ3AJbMIEHxasKOFpRdMilzEhiJ6Rt5Ukw0DWZ+uEQNcTGUSkDwdHbhpozl5k+Yw1I8KSPXotVaXmRHaqlPdTxsetVoUzTDfnhnYsnD4Ypowp+8mwDs9qO2V7CcBkj67+w45OtLVPfbE8LXAbo7xnORg3yz5hiRp/JIQg7i+Ih9iwOI2ho+ZruNdkijHeABXEK2L612iX+D7b5fmV7YDS+BgIIEwlug+GGtVnGvYr33O2ox 0qarepF4 DiFq5d8z/hPcAQdoL3JLlVTbI6e8tK+7rss0HuopWSOZbwRqr8hChAwtPNB1ohWQ/69xJS6BT2RHZY62LSUfTpZQWqRcOd5BcDzH363zDaHERaG2+pZheOeofJkz+Gdm4HzDBGSYNhc4UNCRw8SnYe783So4MCmecComgfFr6DTl++7F2wc7sL7RWXXwcXdI92P9dyMneHXEqXa4Ru6hw9mqbTzAnrJkguk6T 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