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Thu, 22 Apr 2021 22:42:00 +0000 (UTC) Received: from [10.64.54.94] (vpn2-54-94.bne.redhat.com [10.64.54.94]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1B2F85C3E0; Thu, 22 Apr 2021 22:41:57 +0000 (UTC) Subject: Re: [PATCH v4 2/2] kvm/arm64: Try stage2 block mapping for host device MMIO To: Marc Zyngier Cc: Keqian Zhu , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, wanghaibin.wang@huawei.com References: <20210415140328.24200-1-zhukeqian1@huawei.com> <20210415140328.24200-3-zhukeqian1@huawei.com> <960e097d-818b-00bc-b2ee-0da17857f862@redhat.com> <105a403a-e48b-15bc-44ff-0ff34f7d2194@huawei.com> <46606f3e-ef41-6520-6647-88c0f76a83e0@redhat.com> <87tunyq0av.wl-maz@kernel.org> From: Gavin Shan Message-ID: Date: Fri, 23 Apr 2021 10:42:08 +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: <87tunyq0av.wl-maz@kernel.org> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210422_154206_027928_6338E6B1 X-CRM114-Status: GOOD ( 25.27 ) 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 Marc, On 4/22/21 4:51 PM, Marc Zyngier wrote: > On Thu, 22 Apr 2021 03:25:23 +0100, > Gavin Shan wrote: >> On 4/21/21 4:36 PM, Keqian Zhu wrote: >>> On 2021/4/21 15:52, Gavin Shan wrote: >>>> 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. >>> Yes, but we're not sure all drivers follow this rule. Add a BUG_ON() is >>> a way to catch issue. >>> >> >> I think I didn't make things clear. What I meant is VM_PFNMAP can't >> be set for hugetlbfs VMAs. So the checks here can be simplified as >> below if you agree: >> >> if (is_vm_hugetlb_page(vma)) >> return huge_page_shift(hstate_vma(vma)); >> >> if (!(vma->vm_flags & VM_PFNMAP)) >> return PAGE_SHIFT; >> >> VM_BUG_ON(is_vm_hugetlb_page(vma)); /* Can be dropped */ > > No. If this case happens, I want to see it. I have explicitly asked > for it, and this check stays. > Thanks for the explanation. To keep VM_BUG_ON() sounds good to me too :) Thanks, Gavin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel