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0CRPkrt+fFN1Hrd+AOozAFeN6nCFsLkJniQ1Oiagb6KM0yfRPdjnuFTcXkO8YeiAsIEPJBQ/zQYjGewjepLVJftWN+18RNm/ta/WRNUQ/oZv8B+UP7aJ7WuiDZT57v+nkGVQO13TLezRfUtI5QGr37EauFbYBABAVMgSvf3wdK5AIoKC9uVkape0ThIdLJ+g+rG9AH65oRjSdo+VIOuLHoCeQrk3Y3ZUAd0ctXVxvcsNBQH5j+3zduflpjLnwBUVPNTb+mo4zpujP4T2fVNfQmYRJ5rIml41Ey0z29eWUYRb+2XbYXnlf8JA7XMOHugv3sTnfMaRVXWkdFUZS9KLprk0ZWu76c/v2Ai4NRb8CwxhUGmaP/cuR0xeeMQiiauRwF/i/ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000173, 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 Tue, Oct 15, 2024 at 01:13:22PM +0200, Thomas Hellström wrote: > Introduce a way for hmm_range_fault() and migrate_vma_setup() to identify > foreign devices with fast interconnect and thereby allow > both direct access over the interconnect and p2p migration. > > The need for a callback arises because without it, the p2p ability would > need to be static and determined at dev_pagemap creation time. With > a callback it can be determined dynamically, and in the migrate case > the callback could separate out local device pages. > +static bool hmm_allow_devmem(struct hmm_range *range, struct page *page) > +{ > + if (likely(page->pgmap->owner == range->dev_private_owner)) > + return true; > + if (likely(!range->p2p)) > + return false; > + return range->p2p->ops->p2p_allow(range->p2p, page); > +} > + > static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr, > unsigned long end, pmd_t *pmdp, pte_t *ptep, > unsigned long *hmm_pfn) > @@ -248,8 +258,7 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr, > * just report the PFN. > */ > if (is_device_private_entry(entry) && > - pfn_swap_entry_to_page(entry)->pgmap->owner == > - range->dev_private_owner) { > + hmm_allow_devmem(range, pfn_swap_entry_to_page(entry))) { > cpu_flags = HMM_PFN_VALID; > if (is_writable_device_private_entry(entry)) > cpu_flags |= HMM_PFN_WRITE; This is really misnamed and took me a while to get it. It has nothing to do with kernel P2P, you are just allowing more selective filtering of dev_private_owner. You should focus on that in the naming, not p2p. ie allow_dev_private() P2P is stuff that is dealing with MEMORY_DEVICE_PCI_P2PDMA. This is just allowing more instances of the same driver to co-ordinate their device private memory handle, for whatever purpose. Otherwise I don't see a particular problem, though we have talked about widening the matching for device_private more broadly using some kind of grouping tag or something like that instead of a callback. You may consider that as an alternative I would also probably try to have less indirection, you can embedd the hmm_range struct inside a caller private data struct and use that instead if inventing a whole new struct and pointer. Jason