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Wed, 21 Apr 2021 05:52:52 +0000 (UTC) Received: from [10.64.54.47] (vpn2-54-47.bne.redhat.com [10.64.54.47]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 39B086064B; Wed, 21 Apr 2021 05:52:48 +0000 (UTC) Subject: Re: [PATCH v4 2/2] kvm/arm64: Try stage2 block mapping for host device MMIO To: Keqian Zhu , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, Marc Zyngier Cc: wanghaibin.wang@huawei.com References: <20210415140328.24200-1-zhukeqian1@huawei.com> <20210415140328.24200-3-zhukeqian1@huawei.com> From: Gavin Shan Message-ID: <960e097d-818b-00bc-b2ee-0da17857f862@redhat.com> Date: Wed, 21 Apr 2021 17:52:58 +1000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0 MIME-Version: 1.0 In-Reply-To: <20210415140328.24200-3-zhukeqian1@huawei.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210420_225259_023445_8C5C6F3E X-CRM114-Status: GOOD ( 42.26 ) 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: , Reply-To: Gavin Shan Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Keqian, On 4/16/21 12:03 AM, 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 get_vma_page_shift() to get page shift for both normal > memory and device MMIO region, and check these two points when > selecting block mapping size for MMIO region. > > Signed-off-by: Keqian Zhu > --- > arch/arm64/kvm/mmu.c | 61 ++++++++++++++++++++++++++++++++++++-------- > 1 file changed, 51 insertions(+), 10 deletions(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index c59af5ca01b0..5a1cc7751e6d 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)); > + I don't understand how VM_PFNMAP is set for hugetlbfs related vma. I think they are exclusive, meaning the flag is never set for hugetlbfs vma. If it's true, VM_PFNMAP needn't be checked on hugetlbfs vma and the VM_BUG_ON() becomes unnecessary. > + 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; > +} > + There is "switch(...)" fallback mechanism in user_mem_abort(). PUD_SIZE/PMD_SIZE can be downgraded accordingly if the addresses fails in the alignment check by fault_supports_stage2_huge_mapping(). I think it would make user_mem_abort() simplified if the logic can be moved to get_vma_page_shift(). Another question if we need the check from fault_supports_stage2_huge_mapping() if VM_PFNMAP area is going to be covered by block mapping. If so, the "switch(...)" fallback mechanism needs to be part of get_vma_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) > @@ -769,7 +798,10 @@ 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)) { > @@ -778,15 +810,15 @@ 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; > - > - if (logging_active || > - (vma->vm_flags & VM_PFNMAP)) { > + /* > + * logging_active is guaranteed to never be true for VM_PFNMAP > + * memslots. > + */ > + if (logging_active) { > force_pte = true; > vma_shift = PAGE_SHIFT; > + } else { > + vma_shift = get_vma_page_shift(vma, hva); > } > > switch (vma_shift) { > @@ -854,8 +886,17 @@ 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 +917,7 @@ 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) > Thanks, Gavin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel