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[PATCH] mm/hmm: Do not fault in device private pages owned by the caller To: Francois Dugast Cc: airlied@gmail.com, akpm@linux-foundation.org, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, dakr@kernel.org, david@redhat.com, donettom@linux.ibm.com, jane.chu@oracle.com, jglisse@redhat.com, kherbst@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lyude@redhat.com, matthew.brost@intel.com, peterx@redhat.com, ryan.roberts@arm.com, shuah@kernel.org, simona@ffwll.ch, wangkefeng.wang@huawei.com, willy@infradead.org, ziy@nvidia.com References: <9ae3e014-c7d0-4d58-af0e-925bcd9e4cfd@nvidia.com> <20250722193445.1588348-1-francois.dugast@intel.com> Content-Language: en-US From: Balbir Singh In-Reply-To: <20250722193445.1588348-1-francois.dugast@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BY5PR17CA0038.namprd17.prod.outlook.com (2603:10b6:a03:167::15) To PH8PR12MB7277.namprd12.prod.outlook.com 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 rjp1QJ3c 13kSzhOpGinSMtCvxoPzNAYjRttZNn7NQ4Xfdiqzcp7tJ7UDSbG4xkYiiyzQWd/Ywnq2783swy21l4QV31ddLXU5QW+8KIRFaI7HYw1Wda83E9eBihXxUP46Eg4sIrN6w272ep1JT8R/4CdGp8g6KOhEChqXY8Ra2kwAvfvap6PODYr89ON1Q9saKkPZf3cY5d/MwxFHA1UOuHLTNtR4PLKchuX4NTCe/DXXC7ZLUa8iyMPOjwjgme6FUTy4+mRYqEfxLwhZxKaN9Zz9vPMOTfjf3fchKokl3JJCNbVJZEICRxGCifGFAS+EMf7knrbuN+JzDau3d63WuqgIaXB29Ny4y518j0OXydZ9YbxEWObab4GkF21Nje3lKpr872JvTV82SQjD2MWbMZ2VubeyILCkjA7efpa1WuYIHOYXOE4zmEGvAeBl5lqspx5yd+i/yjCWRVWlWwWhH0wdgUD8HUHjHlNrTsffb2BpQWPsIgAFmik/DRdxfxgDK8WHx95Ul3JVUiqLI3yO/rv8= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/23/25 05:34, Francois Dugast wrote: > When the PMD swap entry is device private and owned by the caller, > skip the range faulting and instead just set the correct HMM PFNs. > This is similar to the logic for PTEs in hmm_vma_handle_pte(). > > For now, each hmm_pfns[i] entry is populated as it is currently done > in hmm_vma_handle_pmd() but this might not be necessary. A follow-up > optimization could be to make use of the order and skip populating > subsequent PFNs. I think we should test and remove these now > > Signed-off-by: Francois Dugast > --- > mm/hmm.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/mm/hmm.c b/mm/hmm.c > index f2415b4b2cdd..63ec1b18a656 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -355,6 +355,31 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, > } > > if (!pmd_present(pmd)) { > + swp_entry_t entry = pmd_to_swp_entry(pmd); > + > + /* > + * Don't fault in device private pages owned by the caller, > + * just report the PFNs. > + */ > + if (is_device_private_entry(entry) && > + pfn_swap_entry_folio(entry)->pgmap->owner == > + range->dev_private_owner) { > + unsigned long cpu_flags = HMM_PFN_VALID | > + hmm_pfn_flags_order(PMD_SHIFT - PAGE_SHIFT); > + unsigned long pfn = swp_offset_pfn(entry); > + unsigned long i; > + > + if (is_writable_device_private_entry(entry)) > + cpu_flags |= HMM_PFN_WRITE; > + > + for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++) { > + hmm_pfns[i] &= HMM_PFN_INOUT_FLAGS; > + hmm_pfns[i] |= pfn | cpu_flags; > + } > + As discussed, can we remove these. > + return 0; > + } All of this be under CONFIG_ARCH_ENABLE_THP_MIGRATION > + > if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0)) > return -EFAULT; > return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR); Balbir Singh