From: Will Deacon <will@kernel.org> To: Linus Torvalds <torvalds@linux-foundation.org> Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>, Linux ARM <linux-arm-kernel@lists.infradead.org>, Catalin Marinas <catalin.marinas@arm.com>, Jan Kara <jack@suse.cz>, Minchan Kim <minchan@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, Vinayak Menon <vinmenon@codeaurora.org>, Android Kernel Team <kernel-team@android.com> Subject: Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting Date: Wed, 9 Dec 2020 18:40:50 +0000 [thread overview] Message-ID: <20201209184049.GA8778@willie-the-truck> (raw) In-Reply-To: <CAHk-=wgos=vgteG52=J=rVSeq6-Y2g2+Kn1=xV=wYjVzM6O9UQ@mail.gmail.com> On Wed, Dec 09, 2020 at 09:58:12AM -0800, Linus Torvalds wrote: > On Wed, Dec 9, 2020 at 8:40 AM Will Deacon <will@kernel.org> wrote: > > > > @@ -3978,8 +3994,17 @@ static vm_fault_t do_fault_around(struct vm_fault *vmf) > > > > /* check if the page fault is solved */ > > vmf->pte -= (vmf->address >> PAGE_SHIFT) - (address >> PAGE_SHIFT); > > - if (!pte_none(*vmf->pte)) > > - ret = VM_FAULT_NOPAGE; > > + if (pte_none(*vmf->pte)) > > + goto out_unlock; > > + > > + if (vmf->flags & FAULT_FLAG_PREFAULT_OLD) { > > + pte_t pte = pte_mkyoung(*vmf->pte); > > + if (ptep_set_access_flags(vmf->vma, address, vmf->pte, pte, 0)) > > + update_mmu_cache(vmf->vma, address, vmf->pte); > > + } > > Oh, please dear God no. > > First you incorrectly set it old, and then you conditionally make it > young again and as a result force an atomic rwm update and another TLB > flush for no good reason. There shouldn't be a TLB flush here, but I agree that it would have to go and nobble the hash for PowerPC if they wanted to enable this. > Just make sure that the FAULT_FLAG_PREFAULT_OLD never sets the > *actual* address to old. > > And yes, that probably means that you need to change "alloc_set_pte()" > to actually pass in the real address, and leave "vmf->address" alone - > so that it can know which ones are prefaulted and which one is real, > but that sounds like a good idea anyway. Right, I deliberately avoided that based on the feedback from Jan on an older version [1], but I can certainly look at it again. > Then you can just make alloc_set_pte() do the right thing in the first > place, instead of doing this nasty "lets do it wrong and fix it up > later" horror. I'll have a crack at this in v2. Cheers, Will [1] https://patchwork.kernel.org/project/linux-arm-kernel/patch/1511845670-12133-1-git-send-email-vinmenon@codeaurora.org/
WARNING: multiple messages have this Message-ID (diff)
From: Will Deacon <will@kernel.org> To: Linus Torvalds <torvalds@linux-foundation.org> Cc: Jan Kara <jack@suse.cz>, Minchan Kim <minchan@kernel.org>, Catalin Marinas <catalin.marinas@arm.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>, Vinayak Menon <vinmenon@codeaurora.org>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, Andrew Morton <akpm@linux-foundation.org>, Android Kernel Team <kernel-team@android.com>, Linux ARM <linux-arm-kernel@lists.infradead.org> Subject: Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting Date: Wed, 9 Dec 2020 18:40:50 +0000 [thread overview] Message-ID: <20201209184049.GA8778@willie-the-truck> (raw) In-Reply-To: <CAHk-=wgos=vgteG52=J=rVSeq6-Y2g2+Kn1=xV=wYjVzM6O9UQ@mail.gmail.com> On Wed, Dec 09, 2020 at 09:58:12AM -0800, Linus Torvalds wrote: > On Wed, Dec 9, 2020 at 8:40 AM Will Deacon <will@kernel.org> wrote: > > > > @@ -3978,8 +3994,17 @@ static vm_fault_t do_fault_around(struct vm_fault *vmf) > > > > /* check if the page fault is solved */ > > vmf->pte -= (vmf->address >> PAGE_SHIFT) - (address >> PAGE_SHIFT); > > - if (!pte_none(*vmf->pte)) > > - ret = VM_FAULT_NOPAGE; > > + if (pte_none(*vmf->pte)) > > + goto out_unlock; > > + > > + if (vmf->flags & FAULT_FLAG_PREFAULT_OLD) { > > + pte_t pte = pte_mkyoung(*vmf->pte); > > + if (ptep_set_access_flags(vmf->vma, address, vmf->pte, pte, 0)) > > + update_mmu_cache(vmf->vma, address, vmf->pte); > > + } > > Oh, please dear God no. > > First you incorrectly set it old, and then you conditionally make it > young again and as a result force an atomic rwm update and another TLB > flush for no good reason. There shouldn't be a TLB flush here, but I agree that it would have to go and nobble the hash for PowerPC if they wanted to enable this. > Just make sure that the FAULT_FLAG_PREFAULT_OLD never sets the > *actual* address to old. > > And yes, that probably means that you need to change "alloc_set_pte()" > to actually pass in the real address, and leave "vmf->address" alone - > so that it can know which ones are prefaulted and which one is real, > but that sounds like a good idea anyway. Right, I deliberately avoided that based on the feedback from Jan on an older version [1], but I can certainly look at it again. > Then you can just make alloc_set_pte() do the right thing in the first > place, instead of doing this nasty "lets do it wrong and fix it up > later" horror. I'll have a crack at this in v2. Cheers, Will [1] https://patchwork.kernel.org/project/linux-arm-kernel/patch/1511845670-12133-1-git-send-email-vinmenon@codeaurora.org/ _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-12-09 18:42 UTC|newest] Thread overview: 138+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-12-09 16:39 [PATCH 0/2] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag Will Deacon 2020-12-09 16:39 ` Will Deacon 2020-12-09 16:39 ` [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting Will Deacon 2020-12-09 16:39 ` Will Deacon 2020-12-09 17:58 ` Linus Torvalds 2020-12-09 17:58 ` Linus Torvalds 2020-12-09 17:58 ` Linus Torvalds 2020-12-09 18:40 ` Will Deacon [this message] 2020-12-09 18:40 ` Will Deacon 2020-12-09 19:04 ` Linus Torvalds 2020-12-09 19:04 ` Linus Torvalds 2020-12-09 19:04 ` Linus Torvalds 2020-12-09 20:32 ` Matthew Wilcox 2020-12-09 20:32 ` Matthew Wilcox 2020-12-09 21:04 ` Linus Torvalds 2020-12-09 21:04 ` Linus Torvalds 2020-12-09 21:04 ` Linus Torvalds 2020-12-10 15:08 ` Kirill A. Shutemov 2020-12-10 15:08 ` Kirill A. Shutemov 2020-12-10 17:23 ` Linus Torvalds 2020-12-10 17:23 ` Linus Torvalds 2020-12-10 17:23 ` Linus Torvalds 2020-12-14 16:07 ` Kirill A. Shutemov 2020-12-14 16:07 ` Kirill A. Shutemov 2020-12-14 17:54 ` Linus Torvalds 2020-12-14 17:54 ` Linus Torvalds 2020-12-14 17:54 ` Linus Torvalds 2020-12-14 18:56 ` Matthew Wilcox 2020-12-14 18:56 ` Matthew Wilcox 2020-12-16 17:07 ` Kirill A. Shutemov 2020-12-16 17:07 ` Kirill A. Shutemov 2020-12-16 18:41 ` Linus Torvalds 2020-12-16 18:41 ` Linus Torvalds 2020-12-16 18:41 ` Linus Torvalds 2020-12-17 10:54 ` Kirill A. Shutemov 2020-12-17 10:54 ` Kirill A. Shutemov 2020-12-17 18:22 ` Linus Torvalds 2020-12-17 18:22 ` Linus Torvalds 2020-12-17 18:22 ` Linus Torvalds 2020-12-18 11:04 ` Kirill A. Shutemov 2020-12-18 11:04 ` Kirill A. Shutemov 2020-12-18 18:56 ` Linus Torvalds 2020-12-18 18:56 ` Linus Torvalds 2020-12-18 18:56 ` Linus Torvalds 2020-12-19 12:41 ` Kirill A. Shutemov 2020-12-19 12:41 ` Kirill A. Shutemov 2020-12-19 20:08 ` Linus Torvalds 2020-12-19 20:08 ` Linus Torvalds 2020-12-19 20:08 ` Linus Torvalds 2020-12-19 20:34 ` Linus Torvalds 2020-12-19 20:34 ` Linus Torvalds 2020-12-19 20:34 ` Linus Torvalds 2020-12-22 10:00 ` Kirill A. Shutemov 2020-12-22 10:00 ` Kirill A. Shutemov 2020-12-24 4:04 ` Hugh Dickins 2020-12-24 4:04 ` Hugh Dickins 2020-12-24 4:04 ` Hugh Dickins 2020-12-25 11:31 ` Kirill A. Shutemov 2020-12-25 11:31 ` Kirill A. Shutemov 2020-12-26 17:57 ` Linus Torvalds 2020-12-26 17:57 ` Linus Torvalds 2020-12-26 17:57 ` Linus Torvalds 2020-12-26 20:43 ` Kirill A. Shutemov 2020-12-26 20:43 ` Kirill A. Shutemov 2020-12-26 21:03 ` Hugh Dickins 2020-12-26 21:03 ` Hugh Dickins 2020-12-26 21:03 ` Hugh Dickins 2020-12-26 21:16 ` Linus Torvalds 2020-12-26 21:16 ` Linus Torvalds 2020-12-26 21:16 ` Linus Torvalds 2020-12-26 22:40 ` Kirill A. Shutemov 2020-12-26 22:40 ` Kirill A. Shutemov 2020-12-27 0:45 ` Hugh Dickins 2020-12-27 0:45 ` Hugh Dickins 2020-12-27 0:45 ` Hugh Dickins 2020-12-27 2:38 ` Hugh Dickins 2020-12-27 2:38 ` Hugh Dickins 2020-12-27 2:38 ` Hugh Dickins 2020-12-27 19:38 ` Linus Torvalds 2020-12-27 19:38 ` Linus Torvalds 2020-12-27 19:38 ` Linus Torvalds 2020-12-27 20:32 ` Damian Tometzki 2020-12-27 20:32 ` Damian Tometzki 2020-12-27 22:35 ` Hugh Dickins 2020-12-27 22:35 ` Hugh Dickins 2020-12-27 22:35 ` Hugh Dickins 2020-12-27 23:12 ` Linus Torvalds 2020-12-27 23:12 ` Linus Torvalds 2020-12-27 23:12 ` Linus Torvalds 2020-12-27 23:40 ` Linus Torvalds 2020-12-27 23:40 ` Linus Torvalds 2020-12-27 23:40 ` Linus Torvalds 2020-12-27 23:55 ` Kirill A. Shutemov 2020-12-27 23:55 ` Kirill A. Shutemov 2020-12-27 23:48 ` Kirill A. Shutemov 2020-12-27 23:48 ` Kirill A. Shutemov 2020-12-28 1:54 ` Linus Torvalds 2020-12-28 1:54 ` Linus Torvalds 2020-12-28 1:54 ` Linus Torvalds 2020-12-28 6:43 ` Hugh Dickins 2020-12-28 6:43 ` Hugh Dickins 2020-12-28 6:43 ` Hugh Dickins 2020-12-28 12:53 ` Kirill A. Shutemov 2020-12-28 12:53 ` Kirill A. Shutemov 2020-12-28 18:47 ` Linus Torvalds 2020-12-28 18:47 ` Linus Torvalds 2020-12-28 18:47 ` Linus Torvalds 2020-12-28 21:58 ` Linus Torvalds 2020-12-28 21:58 ` Linus Torvalds 2020-12-28 21:58 ` Linus Torvalds 2020-12-29 13:28 ` Kirill A. Shutemov 2020-12-29 13:28 ` Kirill A. Shutemov 2020-12-29 15:19 ` Matthew Wilcox 2020-12-29 15:19 ` Matthew Wilcox 2020-12-29 20:52 ` Linus Torvalds 2020-12-29 20:52 ` Linus Torvalds 2020-12-29 20:52 ` Linus Torvalds 2020-12-28 22:05 ` Kirill A. Shutemov 2020-12-28 22:05 ` Kirill A. Shutemov 2020-12-28 22:12 ` Kirill A. Shutemov 2020-12-28 22:12 ` Kirill A. Shutemov 2020-12-29 4:35 ` Hugh Dickins 2020-12-29 4:35 ` Hugh Dickins 2020-12-29 4:35 ` Hugh Dickins 2020-12-28 23:28 ` Linus Torvalds 2020-12-28 23:28 ` Linus Torvalds 2020-12-28 23:28 ` Linus Torvalds 2020-12-26 21:07 ` Linus Torvalds 2020-12-26 21:07 ` Linus Torvalds 2020-12-26 21:07 ` Linus Torvalds 2020-12-26 21:41 ` Matthew Wilcox 2020-12-26 21:41 ` Matthew Wilcox 2020-12-09 16:39 ` [PATCH 2/2] arm64: mm: Implement arch_wants_old_faultaround_pte() Will Deacon 2020-12-09 16:39 ` Will Deacon 2020-12-09 18:35 ` Catalin Marinas 2020-12-09 18:35 ` Catalin Marinas 2020-12-09 18:46 ` Will Deacon 2020-12-09 18:46 ` Will Deacon
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