Received-SPF: pass (google.com: domain of linux-kernel+bounces-73543-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Message-ID: <34d76192-d00b-409a-8a1b-11a6c8433d66@zytor.com>
Date: Tue, 20 Feb 2024 10:46:37 -0800
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v4 0/3] Cleanup for PAT
Content-Language: en-US
To: mawupeng <mawupeng1@huawei.com>, akpm@linux-foundation.org,
        dave.hansen@linux.intel.com, luto@kernel.org, tglx@linutronix.de,
        peterz@infradead.org, hpa@zytor.com
Cc: linux-kernel@vger.kernel.org, x86@kernel.org, bp@suse.de, mingo@redhat.com,
        rdunlap@infradead.org, bhelgaas@google.com, linux-mm@kvack.org
References: <20240220034835.507022-1-mawupeng1@huawei.com>
 <07d43633-d707-415d-a662-ecd3a50b12ae@zytor.com>
 <1f98fd3a-9a2c-437e-8e86-8c5f575917df@huawei.com>
From: Xin Li <xin@zytor.com>
Autocrypt: addr=xin@zytor.com; keydata=
 xsDNBGUPz1cBDACS/9yOJGojBFPxFt0OfTWuMl0uSgpwk37uRrFPTTLw4BaxhlFL0bjs6q+0
 2OfG34R+a0ZCuj5c9vggUMoOLdDyA7yPVAJU0OX6lqpg6z/kyQg3t4jvajG6aCgwSDx5Kzg5
 Rj3AXl8k2wb0jdqRB4RvaOPFiHNGgXCs5Pkux/qr0laeFIpzMKMootGa4kfURgPhRzUaM1vy
 bsMsL8vpJtGUmitrSqe5dVNBH00whLtPFM7IbzKURPUOkRRiusFAsw0a1ztCgoFczq6VfAVu
 raTye0L/VXwZd+aGi401V2tLsAHxxckRi9p3mc0jExPc60joK+aZPy6amwSCy5kAJ/AboYtY
 VmKIGKx1yx8POy6m+1lZ8C0q9b8eJ8kWPAR78PgT37FQWKYS1uAroG2wLdK7FiIEpPhCD+zH
 wlslo2ETbdKjrLIPNehQCOWrT32k8vFNEMLP5G/mmjfNj5sEf3IOKgMTMVl9AFjsINLHcxEQ
 6T8nGbX/n3msP6A36FDfdSEAEQEAAc0WWGluIExpIDx4aW5Aenl0b3IuY29tPsLBDQQTAQgA
 NxYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89XBQkFo5qAAhsDBAsJCAcFFQgJCgsFFgID
 AQAACgkQa70OVx2uN1HUpgv/cM2fsFCQodLArMTX5nt9yqAWgA5t1srri6EgS8W3F+3Kitge
 tYTBKu6j5BXuXaX3vyfCm+zajDJN77JHuYnpcKKr13VcZi1Swv6Jx1u0II8DOmoDYLb1Q2ZW
 v83W55fOWJ2g72x/UjVJBQ0sVjAngazU3ckc0TeNQlkcpSVGa/qBIHLfZraWtdrNAQT4A1fa
 sWGuJrChBFhtKbYXbUCu9AoYmmbQnsx2EWoJy3h7OjtfFapJbPZql+no5AJ3Mk9eE5oWyLH+
 QWqtOeJM7kKvn/dBudokFSNhDUw06e7EoVPSJyUIMbYtUO7g2+Atu44G/EPP0yV0J4lRO6EA
 wYRXff7+I1jIWEHpj5EFVYO6SmBg7zF2illHEW31JAPtdDLDHYcZDfS41caEKOQIPsdzQkaQ
 oW2hchcjcMPAfyhhRzUpVHLPxLCetP8vrVhTvnaZUo0xaVYb3+wjP+D5j/3+hwblu2agPsaE
 vgVbZ8Fx3TUxUPCAdr/p73DGg57oHjgezsDNBGUPz1gBDAD4Mg7hMFRQqlzotcNSxatlAQNL
 MadLfUTFz8wUUa21LPLrHBkUwm8RujehJrzcVbPYwPXIO0uyL/F///CogMNx7Iwo6by43KOy
 g89wVFhyy237EY76j1lVfLzcMYmjBoTH95fJC/lVb5Whxil6KjSN/R/y3jfG1dPXfwAuZ/4N
 cMoOslWkfZKJeEut5aZTRepKKF54T5r49H9F7OFLyxrC/uI9UDttWqMxcWyCkHh0v1Di8176
 jjYRNTrGEfYfGxSp+3jYL3PoNceIMkqM9haXjjGl0W1B4BidK1LVYBNov0rTEzyr0a1riUrp
 Qk+6z/LHxCM9lFFXnqH7KWeToTOPQebD2B/Ah5CZlft41i8L6LOF/LCuDBuYlu/fI2nuCc8d
 m4wwtkou1Y/kIwbEsE/6RQwRXUZhzO6llfoN96Fczr/RwvPIK5SVMixqWq4QGFAyK0m/1ap4
 bhIRrdCLVQcgU4glo17vqfEaRcTW5SgX+pGs4KIPPBE5J/ABD6pBnUUAEQEAAcLA/AQYAQgA
 JhYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89ZBQkFo5qAAhsMAAoJEGu9DlcdrjdR4C0L
 /RcjolEjoZW8VsyxWtXazQPnaRvzZ4vhmGOsCPr2BPtMlSwDzTlri8BBG1/3t/DNK4JLuwEj
 OAIE3fkkm+UG4Kjud6aNeraDI52DRVCSx6xff3bjmJsJJMb12mWglN6LjdF6K+PE+OTJUh2F
 dOhslN5C2kgl0dvUuevwMgQF3IljLmi/6APKYJHjkJpu1E6luZec/lRbetHuNFtbh3xgFIJx
 2RpgVDP4xB3f8r0I+y6ua+p7fgOjDLyoFjubRGed0Be45JJQEn7A3CSb6Xu7NYobnxfkwAGZ
 Q81a2XtvNS7Aj6NWVoOQB5KbM4yosO5+Me1V1SkX2jlnn26JPEvbV3KRFcwV5RnDxm4OQTSk
 PYbAkjBbm+tuJ/Sm+5Yp5T/BnKz21FoCS8uvTiziHj2H7Cuekn6F8EYhegONm+RVg3vikOpn
 gao85i4HwQTK9/D1wgJIQkdwWXVMZ6q/OALaBp82vQ2U9sjTyFXgDjglgh00VRAHP7u1Rcu4
 l75w1xInsg==
In-Reply-To: <1f98fd3a-9a2c-437e-8e86-8c5f575917df@huawei.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit

On 2/20/2024 1:06 AM, mawupeng wrote:

> On 2024/2/20 16:37, Xin Li wrote:
>> On 2/19/2024 7:48 PM, Wupeng Ma wrote:
>> follow_phys() was introduced in commit 28b2ee20c7cba ("access_process_vm
>> device memory infrastructure") in 2008 for getting a physical page address
>> for a virtual address, and used in generic_access_phys(). And later it's
>> used in x86 PAT code.
>>
>> Commit 03668a4debf4f ("mm: use generic follow_pte() in follow_phys()") made
>> follow_phys() more of a wrapper of follow_pte(), and commit 96667f8a4382d
>> ("mm: Close race in generic_access_phys") replaced follow_phys() with
>> follow_pte() in generic_access_phys(). And the end result is that
>> follow_phys() is used in x86 PAT code only.
> 
> Thanks for the explanation. I have a better understanding of the history of
> this function.
> 

"git blame" tells the story.

>>
>> As follow_phys() in untrack_pfn() can be replaced with follow_pfn(), then
> 
> Yes, this can be replaced with follow_pfn().
> 
>> maybe we don't have to keep follow_phys(), and just use follow_pte() in
>> track_pfn_copy()?
> 
> As follow_phys() will return unsigned long *prot which is need in track_pfn_copy(),
> we need to do something with this.

Commit 96667f8a4382d did that already.

> Can we replace follow_pfn with follow_phys()?

Sorry, I don't get your point.

Thanks!
     Xin