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Thu, 15 Apr 2021 13:46:38 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AAF116113B; Thu, 15 Apr 2021 13:46:35 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94) (envelope-from ) id 1lX2KH-007ehD-Ke; Thu, 15 Apr 2021 14:46:33 +0100 Date: Thu, 15 Apr 2021 14:46:32 +0100 Message-ID: <87eefbmzif.wl-maz@kernel.org> From: Marc Zyngier To: Keqian Zhu Cc: , , , , , Santosh Shukla Subject: Re: [PATCH v3 2/2] kvm/arm64: Try stage2 block mapping for host device MMIO In-Reply-To: <7b5789fb-920d-e797-ba7a-49780bd3d587@huawei.com> References: <20210414065109.8616-1-zhukeqian1@huawei.com> <20210414065109.8616-3-zhukeqian1@huawei.com> <87pmyxme2m.wl-maz@kernel.org> <87im4nn8wf.wl-maz@kernel.org> <7b5789fb-920d-e797-ba7a-49780bd3d587@huawei.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: zhukeqian1@huawei.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, wanghaibin.wang@huawei.com, sashukla@nvidia.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210415_064636_369931_6C531537 X-CRM114-Status: GOOD ( 75.46 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, 15 Apr 2021 12:26:26 +0100, Keqian Zhu wrote: > > Hi Marc, > > On 2021/4/15 18:23, Marc Zyngier wrote: > > On Thu, 15 Apr 2021 03:20:52 +0100, > > Keqian Zhu wrote: > >> > >> Hi Marc, > >> > >> On 2021/4/14 17:05, Marc Zyngier wrote: > >>> + Santosh, who found some interesting bugs in that area before. > >>> > >>> On Wed, 14 Apr 2021 07:51:09 +0100, > >>> Keqian Zhu wrote: > >>>> > >>>> The MMIO region of a device maybe huge (GB level), try to use > >>>> block mapping in stage2 to speedup both map and unmap. > >>>> > >>>> Compared to normal memory mapping, we should consider two more > >>>> points when try block mapping for MMIO region: > >>>> > >>>> 1. For normal memory mapping, the PA(host physical address) and > >>>> HVA have same alignment within PUD_SIZE or PMD_SIZE when we use > >>>> the HVA to request hugepage, so we don't need to consider PA > >>>> alignment when verifing block mapping. But for device memory > >>>> mapping, the PA and HVA may have different alignment. > >>>> > >>>> 2. For normal memory mapping, we are sure hugepage size properly > >>>> fit into vma, so we don't check whether the mapping size exceeds > >>>> the boundary of vma. But for device memory mapping, we should pay > >>>> attention to this. > >>>> > >>>> This adds device_rough_page_shift() to check these two points when > >>>> selecting block mapping size. > >>>> > >>>> Signed-off-by: Keqian Zhu > >>>> --- > >>>> arch/arm64/kvm/mmu.c | 37 +++++++++++++++++++++++++++++++++---- > >>>> 1 file changed, 33 insertions(+), 4 deletions(-) > >>>> > >>>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > >>>> index c59af5ca01b0..1a6d96169d60 100644 > >>>> --- a/arch/arm64/kvm/mmu.c > >>>> +++ b/arch/arm64/kvm/mmu.c > >>>> @@ -624,6 +624,31 @@ static void kvm_send_hwpoison_signal(unsigned long address, short lsb) > >>>> send_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb, current); > >>>> } > >>>> > >>>> +/* > >>>> + * Find a max mapping size that properly insides the vma. And hva and pa must > >>>> + * have the same alignment to this mapping size. It's rough as there are still > >>>> + * other restrictions, will be checked by fault_supports_stage2_huge_mapping(). > >>>> + */ > >>>> +static short device_rough_page_shift(struct vm_area_struct *vma, > >>>> + unsigned long hva) > >>> > >>> My earlier question still stands. Under which circumstances would this > >>> function return something that is *not* the final mapping size? I > >>> really don't see a reason why this would not return the final mapping > >>> size. > >> > >> IIUC, all the restrictions are about alignment and area boundary. > >> > >> That's to say, HVA, IPA and PA must have same alignment within the > >> mapping size. And the areas are memslot and vma, which means the > >> mapping size must properly fit into the memslot and vma. > >> > >> In this function, we just checked the alignment of HVA and PA, and > >> the boundary of vma. So we still need to check the alignment of HVA > >> and IPA, and the boundary of memslot. These will be checked by > >> fault_supports_stage2_huge_mapping(). > > > > But that's no different from what we do with normal memory, is it? So > > it really feels like we should have *one* function that deals with > > establishing the basic mapping size from the VMA (see below for what I > > have in mind). > Right. And it looks better. > > > > >> > >>> > >>>> +{ > >>>> + phys_addr_t pa = (vma->vm_pgoff << PAGE_SHIFT) + (hva - vma->vm_start); > >>>> + > >>>> +#ifndef __PAGETABLE_PMD_FOLDED > >>>> + if ((hva & (PUD_SIZE - 1)) == (pa & (PUD_SIZE - 1)) && > >>>> + ALIGN_DOWN(hva, PUD_SIZE) >= vma->vm_start && > >>>> + ALIGN(hva, PUD_SIZE) <= vma->vm_end) > >>>> + return PUD_SHIFT; > >>>> +#endif > >>>> + > >>>> + if ((hva & (PMD_SIZE - 1)) == (pa & (PMD_SIZE - 1)) && > >>>> + ALIGN_DOWN(hva, PMD_SIZE) >= vma->vm_start && > >>>> + ALIGN(hva, PMD_SIZE) <= vma->vm_end) > >>>> + return PMD_SHIFT; > >>>> + > >>>> + return PAGE_SHIFT; > >>>> +} > >>>> + > >>>> static bool fault_supports_stage2_huge_mapping(struct kvm_memory_slot *memslot, > >>>> unsigned long hva, > >>>> unsigned long map_size) > >>>> @@ -769,7 +794,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > >>>> return -EFAULT; > >>>> } > >>>> > >>>> - /* Let's check if we will get back a huge page backed by hugetlbfs */ > >>>> + /* > >>>> + * Let's check if we will get back a huge page backed by hugetlbfs, or > >>>> + * get block mapping for device MMIO region. > >>>> + */ > >>>> mmap_read_lock(current->mm); > >>>> vma = find_vma_intersection(current->mm, hva, hva + 1); > >>>> if (unlikely(!vma)) { > >>>> @@ -780,11 +808,12 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > >>>> > >>>> if (is_vm_hugetlb_page(vma)) > >>>> vma_shift = huge_page_shift(hstate_vma(vma)); > >>>> + else if (vma->vm_flags & VM_PFNMAP) > >>>> + vma_shift = device_rough_page_shift(vma, hva); > >>> > >>> What prevents a VMA from having both VM_HUGETLB and VM_PFNMAP? This is > >>> pretty unlikely, but I'd like to see this case catered for. > >>> > >> I'm not sure whether VM_HUGETLB and VM_PFNMAP are compatible, and I > >> failed to find a case. > >> > >> VM_PFNMAP is used for page-ranges managed without "struct page", > >> just pure PFN. IIUC, VM_HUGETLB is used for hugetlbfs, which always > >> has "struct page". So I think they should not be compatible, > >> otherwise it's a bug of driver. > > > > For now, maybe. But huge mappings of PFN could land at some point, and > > it'd be hard to catch. I think this case deserves a VM_BUG_ON(). > OK. > > > > >> > >>>> else > >>>> vma_shift = PAGE_SHIFT; > >>>> > >>>> - if (logging_active || > >>>> - (vma->vm_flags & VM_PFNMAP)) { > >>>> + if (logging_active) { > > > > BTW, don't you introduce a bug here? Logging shouldn't affect device > > mappings. > I think it's not a bug, because for memlsot with VM_PFNMAP, the > logging_active is always false. > > In kvm_arch_prepare_memory_region(), we make sure > KVM_MEM_LOG_DIRTY_PAGES can't be set for a VM_PFNMAP memslot. Then > in __kvm_set_memory_region(), we're sure dirty_bitmap is not > allocated for this memslot. Then memslot_is_logging() will return > false for this memslot. Fair enough. I think the first part is what makes it safe. > > > > > > >>>> force_pte = true; > >>>> vma_shift = PAGE_SHIFT; > >>>> } > >>>> @@ -855,7 +884,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > >>>> > >>>> if (kvm_is_device_pfn(pfn)) { > >>>> device = true; > >>>> - force_pte = true; > >>>> + force_pte = (vma_pagesize == PAGE_SIZE); > >>> > >>> Why do we need to set force_pte if we are already dealing with > >>> PAGE_SIZE? I guess you are doing this for the sake of avoiding the > >>> call to transparent_hugepage_adjust(), right? > >> Yes. > >> > >>> > >>> I'd rather you simply don't try to upgrade a device mapping by > >>> explicitly checking for this and keep force_pte for *memory* > >>> exclusively. > >> Agree, that's better. > >> > >>> > >>> Santosh, can you please take a look at this series and try to see if > >>> the problem you fixed in [1] (which ended up as commit 91a2c34b7d6f) > >>> is still OK with this series? > >> I searched the initial version[*], VM_PFNMAP is set when we call > >> gfn_to_pfn_prot()->vma_mmio_fault()->remap_pfn_range(). Then the > >> check of VM_PFNMAP in user_mem_abort() failed, so we will try to > >> call transparent_hugepage_adjust() for device pfn. > >> > >> In that case, our logic of trying block mapping for MMIO is not > >> used. And we still set force_pte for device pfn, so this bugfix is > >> not affected. Santosh, do you agree that? > > > > But isn't what we just agreed to get rid of just above? > Yes, I agree to get rid of force_pte for device. I'm sure your code > doesn't break the bugfix. > > > > >> > >> I still found that the reason vfio_pci does not have this > >> bug. vfio_pci set VM_PFNMAP for vma when userspace calls mmap(). I > >> will apply this logic for vfio_mdev too, let's see what vfio > >> maintainer think about it. > > > > I think that'd be good to see what Alex thinks about it... > > > > Here's the changes I propose. It is completely untested, of course. > > > > Thanks, > > > > M. > > > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > > index 8711894db8c2..f32d956cc199 100644 > > --- a/arch/arm64/kvm/mmu.c > > +++ b/arch/arm64/kvm/mmu.c > > @@ -738,6 +738,35 @@ transparent_hugepage_adjust(struct kvm_memory_slot *memslot, > > return PAGE_SIZE; > > } > > > > +static int get_vma_page_shift(struct vm_area_struct *vma, unsigned long hva) > > +{ > > + unsigned long pa; > > + > > + if (is_vm_hugetlb_page(vma) && !(vma->vm_flags & VM_PFNMAP)) > > + return huge_page_shift(hstate_vma(vma)); > > + > > + if (!(vma->vm_flags & VM_PFNMAP)) > > + return PAGE_SHIFT; > > + > > + VM_BUG_ON(is_vm_hugetlb_page(vma)); > > + > > + pa = (vma->vm_pgoff << PAGE_SHIFT) + (hva - vma->vm_start); > > + > > +#ifndef __PAGETABLE_PMD_FOLDED > > + if ((hva & (PUD_SIZE - 1)) == (pa & (PUD_SIZE - 1)) && > > + ALIGN_DOWN(hva, PUD_SIZE) >= vma->vm_start && > > + ALIGN(hva, PUD_SIZE) <= vma->vm_end) > > + return PUD_SHIFT; > > +#endif > > + > > + if ((hva & (PMD_SIZE - 1)) == (pa & (PMD_SIZE - 1)) && > > + ALIGN_DOWN(hva, PMD_SIZE) >= vma->vm_start && > > + ALIGN(hva, PMD_SIZE) <= vma->vm_end) > > + return PMD_SHIFT; > > + > > + return PAGE_SHIFT; > > +} > > + > > static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > > struct kvm_memory_slot *memslot, unsigned long hva, > > unsigned long fault_status) > > @@ -778,13 +807,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > > return -EFAULT; > > } > > > > - if (is_vm_hugetlb_page(vma)) > > - vma_shift = huge_page_shift(hstate_vma(vma)); > > - else > > - vma_shift = PAGE_SHIFT; > > + vma_shift = get_vma_page_shift(vma, hva); > > > > - if (logging_active || > > - (vma->vm_flags & VM_PFNMAP)) { > > + if (logging_active && !(vma->vm_flags & VM_PFNMAP)) { > Maybe we don't need this. I can add some comments to explain it. Yeah. Please add something along the lines of: /* logging_active is guaranteed to never be true for VM_PFNMAP memslots */ > > > force_pte = true; > > vma_shift = PAGE_SHIFT; > > } > > @@ -854,8 +879,17 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > > return -EFAULT; > > > > if (kvm_is_device_pfn(pfn)) { > > + /* > > + * If the page was identified as device early by looking at > > + * the VMA flags, vma_pagesize is already representing the > > + * largest quantity we can map. If instead it was mapped > > + * via gfn_to_pfn_prot(), vma_pagesize is set to PAGE_SIZE > > + * and must not be upgraded. > > + * > > + * In both cases, we don't let transparent_hugepage_adjust() > > + * change things at the last minute. > > + */ > > device = true; > > - force_pte = true; > > } else if (logging_active && !write_fault) { > > /* > > * Only actually map the page as writable if this was a write > > @@ -876,7 +910,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > > * If we are not forced to use page mapping, check if we are > > * backed by a THP and thus use block mapping if possible. > > */ > > - if (vma_pagesize == PAGE_SIZE && !force_pte) > > + if (vma_pagesize == PAGE_SIZE && !(force_pte || device)) > > vma_pagesize = transparent_hugepage_adjust(memslot, hva, > > &pfn, &fault_ipa); > > if (writable) > > > Looks good to me. :) > > I will test it. And when I send v4, should I add your Suggested-by or SoB? No need. Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel