From mboxrd@z Thu Jan 1 00:00:00 1970 MIME-Version: 1.0 References: <01998876-7e1e-2b84-cc65-8cda310083f2@siemens.com> <87mtvgwcq9.fsf@xenomai.org> In-Reply-To: From: Greg Gallagher Date: Mon, 8 Mar 2021 02:02:03 -0500 Message-ID: Subject: Re: [PATCH 4.19] ipipe: mm: Restore unCOW support for copy_pte_range Content-Type: text/plain; charset="UTF-8" List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: Philippe Gerum , Xenomai On Sun, Mar 7, 2021 at 8:09 AM Greg Gallagher wrote: > > > On Sun, Mar 7, 2021 at 7:56 AM Jan Kiszka wrote: > >> On 06.03.21 15:58, Philippe Gerum wrote: >> > >> > Jan Kiszka writes: >> > >> >> On 05.03.21 12:38, Jan Kiszka via Xenomai wrote: >> >>> From: Jan Kiszka >> >>> >> >>> This is still needed to avoid that a real-time parent seems minor >> faults >> >>> after forking for shared pages until they are finally unshared. >> >>> >> >>> This missing support became visible in Xenomai when running the >> complete >> >>> smokey test suite on certain architectures/config combinations. >> >>> >> >>> Fixes: 0f0b6099c45f ("ipipe: mm: Drop un-COW from copy_pte_range") >> >>> Signed-off-by: Jan Kiszka >> >>> --- >> >>> >> >>> For discussion. If there is a better pattern in reach, I'm happy to >> go >> >>> that path as well. >> >>> >> >>> Otherwise, this should go into our 4.19 branches (Greg, your arm64 >> isn't >> >>> in sync with noarch, you will need manual merging). Possibly, it >> already >> >>> applies to 5.4 as well, didn't check yet. >> >>> >> >>> mm/memory.c | 76 >> ++++++++++++++++++++++++++++++++++++++++++++++++----- >> >>> 1 file changed, 69 insertions(+), 7 deletions(-) >> >>> >> >>> diff --git a/mm/memory.c b/mm/memory.c >> >>> index 4cc7c72a0b7e..f102f4de2213 100644 >> >>> --- a/mm/memory.c >> >>> +++ b/mm/memory.c >> >>> @@ -141,6 +141,9 @@ EXPORT_SYMBOL(zero_pfn); >> >>> >> >>> unsigned long highest_memmap_pfn __read_mostly; >> >>> >> >>> +static bool cow_user_page(struct page *dst, struct page *src, >> >>> + struct vm_fault *vmf); >> >>> + >> >>> /* >> >>> * CONFIG_MMU architectures set up ZERO_PAGE in their paging_init() >> >>> */ >> >>> @@ -957,8 +960,9 @@ struct page *vm_normal_page_pmd(struct >> vm_area_struct *vma, unsigned long addr, >> >>> >> >>> static inline unsigned long >> >>> copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, >> >>> - pte_t *dst_pte, pte_t *src_pte, struct vm_area_struct >> *vma, >> >>> - unsigned long addr, int *rss) >> >>> + pte_t *dst_pte, pte_t *src_pte, struct vm_area_struct *vma, >> >>> + unsigned long addr, int *rss, pmd_t *src_pmd, >> >>> + struct page *uncow_page) >> >>> { >> >>> unsigned long vm_flags = vma->vm_flags; >> >>> pte_t pte = *src_pte; >> >>> @@ -1036,6 +1040,33 @@ copy_one_pte(struct mm_struct *dst_mm, struct >> mm_struct *src_mm, >> >>> * in the parent and the child >> >>> */ >> >>> if (is_cow_mapping(vm_flags) && pte_write(pte)) { >> >>> +#ifdef CONFIG_IPIPE >> >>> + if (uncow_page) { >> >>> + struct page *old_page = vm_normal_page(vma, addr, >> pte); >> >>> + struct vm_fault vmf; >> >>> + >> >>> + vmf.vma = vma; >> >>> + vmf.address = addr; >> >>> + vmf.orig_pte = pte; >> >>> + vmf.pmd = src_pmd; >> >>> + >> >>> + if (cow_user_page(uncow_page, old_page, &vmf)) { >> >>> + pte = mk_pte(uncow_page, >> vma->vm_page_prot); >> >>> + >> >>> + if (vm_flags & VM_SHARED) >> >>> + pte = pte_mkclean(pte); >> >>> + pte = pte_mkold(pte); >> >>> + >> >>> + page_add_new_anon_rmap(uncow_page, vma, >> addr, >> > >> >>> + false); >> >>> + rss[!!PageAnon(uncow_page)]++; >> >>> + goto out_set_pte; >> >>> + } else { >> >>> + /* unexpected: source page no longer >> present */ >> >>> + WARN_ON_ONCE(1); >> >>> + } >> >>> + } >> >>> +#endif /* CONFIG_IPIPE */ >> >>> ptep_set_wrprotect(src_mm, addr, src_pte); >> >>> pte = pte_wrprotect(pte); >> >>> } >> >>> @@ -1083,13 +1114,27 @@ static int copy_pte_range(struct mm_struct >> *dst_mm, struct mm_struct *src_mm, >> >>> int progress = 0; >> >>> int rss[NR_MM_COUNTERS]; >> >>> swp_entry_t entry = (swp_entry_t){0}; >> >>> - >> >>> + struct page *uncow_page = NULL; >> >>> +#ifdef CONFIG_IPIPE >> >>> + int do_cow_break = 0; >> >>> +again: >> >>> + if (do_cow_break) { >> >>> + uncow_page = alloc_page_vma(GFP_HIGHUSER, vma, addr); >> >>> + if (uncow_page == NULL) >> >>> + return -ENOMEM; >> >>> + do_cow_break = 0; >> >>> + } >> >>> +#else >> >>> again: >> >>> +#endif >> >>> init_rss_vec(rss); >> >>> >> >>> dst_pte = pte_alloc_map_lock(dst_mm, dst_pmd, addr, &dst_ptl); >> >>> - if (!dst_pte) >> >>> + if (!dst_pte) { >> >>> + if (uncow_page) >> >>> + put_page(uncow_page); >> >>> return -ENOMEM; >> >>> + } >> >>> src_pte = pte_offset_map(src_pmd, addr); >> >>> src_ptl = pte_lockptr(src_mm, src_pmd); >> >>> spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); >> >>> @@ -1112,8 +1157,25 @@ static int copy_pte_range(struct mm_struct >> *dst_mm, struct mm_struct *src_mm, >> >>> progress++; >> >>> continue; >> >>> } >> >>> +#ifdef CONFIG_IPIPE >> >>> + if (likely(uncow_page == NULL) && >> likely(pte_present(*src_pte))) { >> >>> + if (is_cow_mapping(vma->vm_flags) && >> >>> + test_bit(MMF_VM_PINNED, &src_mm->flags) && >> >>> + ((vma->vm_flags|src_mm->def_flags) & >> VM_LOCKED)) { >> >>> + arch_leave_lazy_mmu_mode(); >> >>> + spin_unlock(src_ptl); >> >>> + pte_unmap(src_pte); >> >>> + add_mm_rss_vec(dst_mm, rss); >> >>> + pte_unmap_unlock(dst_pte, dst_ptl); >> >>> + cond_resched(); >> >>> + do_cow_break = 1; >> >>> + goto again; >> >>> + } >> >>> + } >> >>> +#endif >> >>> entry.val = copy_one_pte(dst_mm, src_mm, dst_pte, src_pte, >> >>> - vma, addr, rss); >> >>> + vma, addr, rss, src_pmd, >> uncow_page); >> >>> + uncow_page = NULL; >> >>> if (entry.val) >> >>> break; >> >>> progress += 8; >> >>> @@ -2348,8 +2410,8 @@ static inline int pte_unmap_same(struct >> mm_struct *mm, pmd_t *pmd, >> >>> return same; >> >>> } >> >>> >> >>> -static inline bool cow_user_page(struct page *dst, struct page *src, >> >>> - struct vm_fault *vmf) >> >>> +static bool cow_user_page(struct page *dst, struct page *src, >> >>> + struct vm_fault *vmf) >> >>> { >> >>> bool ret; >> >>> void *kaddr; >> >>> >> >> >> >> With this applied to ipipe-4.19 and 5.4 queues, related issues are >> gone, see >> >> >> >> https://source.denx.de/Xenomai/xenomai-images/-/pipelines/6670 >> >> >> >> I'm inclined to take this for now so that we can move forward with >> other >> >> topics. Any comments? >> >> >> > >> > Fine with me. This code can be simplified, working on it. I'll channel >> > this through Dovetail. >> > >> >> OK, applied. >> >> Greg, you can find updated no-arch branches for 4.19 and 5.4. > > >> Did this commit go into the no-arch tree? I'll have new arm/arm64 5.4 and 4.19 releases this week (aiming for Wednesday). Thanks Greg