From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.loongson.cn (mail.loongson.cn [114.242.206.163]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 82E563201; Fri, 14 Jun 2024 02:46:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=114.242.206.163 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718333185; cv=none; b=fQsbQZFj1oA9gMS17QFf5nN0IS6cA8SGHDvr5jmMOeLQ1Mi1YtUwSgX/okX6E/sKN5GjGY28JECQppj8O0HfcB8IIucI0/veKH9Q5BLMn94qLME80laiIla/8k+BiT28+P2W264ePoqqB14SgSQM3yo5LekjDCpeA6wyp8MqTKg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718333185; c=relaxed/simple; bh=zPvvfcrWiryVVmbdckHsbGSqcaJy4UzIjFMflqZUQQE=; h=Subject:To:Cc:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=YzqAGjjgkMkmATEfxfjjk9eZzbOEV43y2el05vu66lp5IbNJ2kmkba6JlwVu5HBHV+5WLs/SsxIHsqaLOXRg0XQJ4VIY2xApf3rFHfVeXjSQcdpQNb51+6wIpiM4astxfcsE6S81vmIFgBH4J9tLmCSfATLOiJG44N8u5XEnkfg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=loongson.cn; spf=pass smtp.mailfrom=loongson.cn; arc=none smtp.client-ip=114.242.206.163 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=loongson.cn Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=loongson.cn Received: from loongson.cn (unknown [10.20.42.62]) by gateway (Coremail) with SMTP id _____8AxW+rnrmtmN8AGAA--.27338S3; Fri, 14 Jun 2024 10:46:00 +0800 (CST) Received: from [10.20.42.62] (unknown [10.20.42.62]) by localhost.localdomain (Coremail) with SMTP id AQAAf8Bx28bkrmtmnKUfAA--.11909S3; Fri, 14 Jun 2024 10:45:59 +0800 (CST) Subject: Re: [PATCH] KVM: Remove duplicated zero clear with dirty_bitmap buffer To: Christophe JAILLET , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20240613125407.1126587-1-maobibo@loongson.cn> <115973a9-caa6-4d53-a477-dea2d2291598@wanadoo.fr> From: maobibo Message-ID: Date: Fri, 14 Jun 2024 10:45:56 +0800 User-Agent: Mozilla/5.0 (X11; Linux loongarch64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <115973a9-caa6-4d53-a477-dea2d2291598@wanadoo.fr> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-CM-TRANSID:AQAAf8Bx28bkrmtmnKUfAA--.11909S3 X-CM-SenderInfo: xpdruxter6z05rqj20fqof0/ X-Coremail-Antispam: 1Uk129KBj93XoWxJrW7urWrGr1fGw4furyxXrc_yoW8Zr13pF s3tFWUGrW5Jw18Cw17Cwn8W348t3yDtwn7Gr1UJFyUXr1kJr1vqr4IgF10g3WUZr4Iy3Wr JF4jqFyUuF1UA3gCm3ZEXasCq-sJn29KB7ZKAUJUUUU5529EdanIXcx71UUUUU7KY7ZEXa sCq-sGcSsGvfJ3Ic02F40EFcxC0VAKzVAqx4xG6I80ebIjqfuFe4nvWSU5nxnvy29KBjDU 0xBIdaVrnRJUUUvFb4IE77IF4wAFF20E14v26r1j6r4UM7CY07I20VC2zVCF04k26cxKx2 IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4vEj48v e4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_JFI_Gr1l84ACjcxK6xIIjxv20xvEc7CjxVAFwI 0_Gr0_Cr1l84ACjcxK6I8E87Iv67AKxVWxJVW8Jr1l84ACjcxK6I8E87Iv6xkF7I0E14v2 6r4UJVWxJr1le2I262IYc4CY6c8Ij28IcVAaY2xG8wAqjxCEc2xF0cIa020Ex4CE44I27w Aqx4xG64xvF2IEw4CE5I8CrVC2j2WlYx0E2Ix0cI8IcVAFwI0_Jrv_JF1lYx0Ex4A2jsIE 14v26r1j6r4UMcvjeVCFs4IE7xkEbVWUJVW8JwACjcxG0xvEwIxGrwCYjI0SjxkI62AI1c AE67vIY487MxAIw28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I8C rVAFwI0_Jr0_Jr4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUAVWUtw CIc40Y0x0EwIxGrwCI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x02 67AKxVWUJVW8JwCI42IY6xAIw20EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI0_Jr 0_Gr1lIxAIcVC2z280aVCY1x0267AKxVWUJVW8JbIYCTnIWIevJa73UjIFyTuYvjxUwmhF DUUUU On 2024/6/14 上午3:25, Christophe JAILLET wrote: > Le 13/06/2024 à 14:54, Bibo Mao a écrit : >> Since dirty_bitmap pointer is allocated with function __vcalloc(), >> there is __GFP_ZERO flag set in the implementation about this function >> __vcalloc_noprof(). It is not necessary to clear dirty_bitmap buffer >> with zero again. >> >> Signed-off-by: Bibo Mao >> --- >>   virt/kvm/kvm_main.c | 3 --- >>   1 file changed, 3 deletions(-) >> > > Hi, > >> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >> index 14841acb8b95..c7d4a041dcfa 100644 >> --- a/virt/kvm/kvm_main.c >> +++ b/virt/kvm/kvm_main.c >> @@ -1669,9 +1669,6 @@ static int kvm_prepare_memory_region(struct kvm >> *kvm, >>               r = kvm_alloc_dirty_bitmap(new); >>               if (r) >>                   return r; >> - >> -            if (kvm_dirty_log_manual_protect_and_init_set(kvm)) >> -                bitmap_set(new->dirty_bitmap, 0, new->npages); > > unless I miss something obvious, this does not clear anything, but set > all bits to 1. > > 0 is not for "write 0" (i.e. clear), but for "start at offset 0". > So all bits are set to 1 in this case. you are right, I had thought it is to write 0 :( I do not know whether KVM_DIRTY_LOG_INITIALLY_SET should be enabled on LoongArch. If it is set, write protection for second MMU will start one by one in function kvm_arch_mmu_enable_log_dirty_pt_masked() when dirty log is cleared if it is set, else write protection will start in function kvm_arch_commit_memory_region() when flag of memslot is changed. I do not see the obvious benefits between these two write protect stages. Can anyone give me any hints? Regards Bibo Mao > > CJ > >>           } >>       } >> >> base-commit: 83a7eefedc9b56fe7bfeff13b6c7356688ffa670