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To allow these to be managed the same as normal pages >> introduce dax_insert_pfn_pmd. This will map the entire PMD-sized folio >> and take references as it would for a normally mapped page. >> >> This is distinct from the current mechanism, vmf_insert_pfn_pmd, which >> simply inserts a special devmap PMD entry into the page table without >> holding a reference to the page for the mapping. > > It would be useful to mention the rationale for the locking changes and > your understanding of the new "pgtable deposit" handling, because those > things make this not a trivial conversion. My intent was not to change the locking for the existing vmf_insert_pfn_pmd() but just to move it up a level in the stack so dax_insert_pfn_pmd() could do the metadata manipulation while holding the lock. Looks like I didn't get that quite right though, so I will review it for the next version. >> >> Signed-off-by: Alistair Popple >> --- >> include/linux/huge_mm.h | 1 +- >> mm/huge_memory.c | 57 ++++++++++++++++++++++++++++++++++-------- >> 2 files changed, 48 insertions(+), 10 deletions(-) >> >> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >> index d3a1872..eaf3f78 100644 >> --- a/include/linux/huge_mm.h >> +++ b/include/linux/huge_mm.h >> @@ -40,6 +40,7 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, >> >> vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write); >> vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write); >> +vm_fault_t dax_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write); >> vm_fault_t dax_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write); >> >> enum transparent_hugepage_flag { >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index e8985a4..790041e 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -1237,14 +1237,12 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, >> { >> struct mm_struct *mm = vma->vm_mm; >> pmd_t entry; >> - spinlock_t *ptl; >> >> - ptl = pmd_lock(mm, pmd); >> if (!pmd_none(*pmd)) { >> if (write) { >> if (pmd_pfn(*pmd) != pfn_t_to_pfn(pfn)) { >> WARN_ON_ONCE(!is_huge_zero_pmd(*pmd)); >> - goto out_unlock; >> + return; >> } >> entry = pmd_mkyoung(*pmd); >> entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); >> @@ -1252,7 +1250,7 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, >> update_mmu_cache_pmd(vma, addr, pmd); >> } >> >> - goto out_unlock; >> + return; >> } >> >> entry = pmd_mkhuge(pfn_t_pmd(pfn, prot)); >> @@ -1271,11 +1269,6 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, >> >> set_pmd_at(mm, addr, pmd, entry); >> update_mmu_cache_pmd(vma, addr, pmd); >> - >> -out_unlock: >> - spin_unlock(ptl); >> - if (pgtable) >> - pte_free(mm, pgtable); >> } >> >> /** >> @@ -1294,6 +1287,7 @@ vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write) >> struct vm_area_struct *vma = vmf->vma; >> pgprot_t pgprot = vma->vm_page_prot; >> pgtable_t pgtable = NULL; >> + spinlock_t *ptl; >> >> /* >> * If we had pmd_special, we could avoid all these restrictions, >> @@ -1316,12 +1310,55 @@ vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write) >> } >> >> track_pfn_insert(vma, &pgprot, pfn); >> - >> + ptl = pmd_lock(vma->vm_mm, vmf->pmd); >> insert_pfn_pmd(vma, addr, vmf->pmd, pfn, pgprot, write, pgtable); >> + spin_unlock(ptl); >> + if (pgtable) >> + pte_free(vma->vm_mm, pgtable); >> + >> return VM_FAULT_NOPAGE; >> } >> EXPORT_SYMBOL_GPL(vmf_insert_pfn_pmd); >> >> +vm_fault_t dax_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write) >> +{ >> + struct vm_area_struct *vma = vmf->vma; >> + unsigned long addr = vmf->address & PMD_MASK; >> + struct mm_struct *mm = vma->vm_mm; >> + spinlock_t *ptl; >> + pgtable_t pgtable = NULL; >> + struct folio *folio; >> + struct page *page; >> + >> + if (addr < vma->vm_start || addr >= vma->vm_end) >> + return VM_FAULT_SIGBUS; >> + >> + if (arch_needs_pgtable_deposit()) { >> + pgtable = pte_alloc_one(vma->vm_mm); >> + if (!pgtable) >> + return VM_FAULT_OOM; >> + } >> + >> + track_pfn_insert(vma, &vma->vm_page_prot, pfn); >> + >> + ptl = pmd_lock(mm, vmf->pmd); >> + if (pmd_none(*vmf->pmd)) { >> + page = pfn_t_to_page(pfn); >> + folio = page_folio(page); >> + folio_get(folio); >> + folio_add_file_rmap_pmd(folio, page, vma); >> + add_mm_counter(mm, mm_counter_file(folio), HPAGE_PMD_NR); >> + } >> + insert_pfn_pmd(vma, addr, vmf->pmd, pfn, vma->vm_page_prot, >> + write, pgtable); >> + spin_unlock(ptl); >> + if (pgtable) >> + pte_free(mm, pgtable); > > Are not the deposit rules that the extra page table stick around for the > lifetime of the inserted pte? So would that not require this incremental > change? Yeah, thanks for catching this. > --- > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index ea65c2db2bb1..5ef1e5d21a96 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1232,7 +1232,7 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf) > > static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, > pmd_t *pmd, unsigned long pfn, pgprot_t prot, > - bool write, pgtable_t pgtable) > + bool write, pgtable_t *pgtable) > { > struct mm_struct *mm = vma->vm_mm; > pmd_t entry; > @@ -1258,10 +1258,10 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, > entry = maybe_pmd_mkwrite(entry, vma); > } > > - if (pgtable) { > - pgtable_trans_huge_deposit(mm, pmd, pgtable); > + if (*pgtable) { > + pgtable_trans_huge_deposit(mm, pmd, *pgtable); > mm_inc_nr_ptes(mm); > - pgtable = NULL; > + *pgtable = NULL; > } > > set_pmd_at(mm, addr, pmd, entry); > @@ -1306,7 +1306,7 @@ vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, unsigned long pfn, bool writ > > track_pfn_insert(vma, &pgprot, pfn); > ptl = pmd_lock(vma->vm_mm, vmf->pmd); > - insert_pfn_pmd(vma, addr, vmf->pmd, pfn, pgprot, write, pgtable); > + insert_pfn_pmd(vma, addr, vmf->pmd, pfn, pgprot, write, &pgtable); > spin_unlock(ptl); > if (pgtable) > pte_free(vma->vm_mm, pgtable); > @@ -1344,8 +1344,8 @@ vm_fault_t dax_insert_pfn_pmd(struct vm_fault *vmf, unsigned long pfn, bool writ > folio_add_file_rmap_pmd(folio, page, vma); > add_mm_counter(mm, mm_counter_file(folio), HPAGE_PMD_NR); > } > - insert_pfn_pmd(vma, addr, vmf->pmd, pfn, vma->vm_page_prot, > - write, pgtable); > + insert_pfn_pmd(vma, addr, vmf->pmd, pfn, vma->vm_page_prot, write, > + &pgtable); > spin_unlock(ptl); > if (pgtable) > pte_free(mm, pgtable); > --- > > Along these lines it would be lovely if someone from the PowerPC side > could test these changes, or if someone has a canned qemu command line > to test radix vs hash with pmem+dax that they can share? Michael, Nick, do you know of a qemu command or anyone who might? >> + >> + return VM_FAULT_NOPAGE; >> +} >> +EXPORT_SYMBOL_GPL(dax_insert_pfn_pmd); > > Like I mentioned before, lets make the exported function > vmf_insert_folio() and move the pte, pmd, pud internal private / static > details of the implementation. The "dax_" specific aspect of this was > removed at the conversion of a dax_pfn to a folio. Ok, let me try that. Note that vmf_insert_pfn{_pmd|_pud} will have to stick around though.