From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f69.google.com (mail-pl0-f69.google.com [209.85.160.69]) by kanga.kvack.org (Postfix) with ESMTP id 157326B0008 for ; Wed, 21 Feb 2018 07:47:21 -0500 (EST) Received: by mail-pl0-f69.google.com with SMTP id o61so737302pld.5 for ; Wed, 21 Feb 2018 04:47:21 -0800 (PST) Received: from huawei.com (szxga02-in.huawei.com. [45.249.212.188]) by mx.google.com with ESMTPS id 33-v6si2269422plg.227.2018.02.21.04.47.19 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 21 Feb 2018 04:47:20 -0800 (PST) From: "Wangxuefeng (E)" Subject: =?gb2312?B?tPC4tDogtPC4tDogW1JGQyBwYXRjaF0gaW9yZW1hcDogZG9uJ3Qgc2V0IHVw?= =?gb2312?Q?_huge_I/O_mappings_when_p4d/pud/pmd_is_zero?= Date: Wed, 21 Feb 2018 12:47:11 +0000 Message-ID: References: <1514460261-65222-1-git-send-email-guohanjun@huawei.com> <861128ce-966f-7006-45ba-6a7298918686@codeaurora.org> <1519175992.16384.121.camel@hpe.com> ,<20180221115758.GA7614@arm.com> In-Reply-To: <20180221115758.GA7614@arm.com> Content-Language: zh-CN Content-Type: multipart/alternative; boundary="_000_etPan5a8d6a4e278c448b3d0elocalhost_" MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: "will.deacon" Cc: "toshi.kani" , linux-arm-kernel , cpandya , linux-kernel , "Guohanjun (Hanjun Guo)" , Linuxarm , linux-mm , akpm , "mark.rutland" , "catalin.marinas" , mhocko , "hanjun.guo" --_000_etPan5a8d6a4e278c448b3d0elocalhost_ Content-Type: text/plain; charset="gb2312" Content-Transfer-Encoding: base64 SGksIFdpbGwNCiAgICAgICBUaGFua3MgZm9yIHlvdXIgZXhwbGFpbi4gSWYgcG1kIGNsZWFyZWQg bWVhbnMgbWFraW5nIHRoZSBwbWQgYW4gaW52YWxpZCBlbnRyeaOsdGhhdKGvIHMgbm8gcHJvYmxl bS4NClRoYW5rcw0KICAgICAgIFdhbmd4dWVmZW5nDQoNClNlbnQgZnJvbSBIVUFXRUkgQW55T2Zm aWNlDQq3orz+yMujundpbGwuZGVhY29uDQrK1bz+yMujug0Ks63LzaO6dG9zaGkua2FuaSxsaW51 eC1hcm0ta2VybmVsLGNwYW5keWEsbGludXgta2VybmVsLLn5uq6+/CxMaW51eGFybSxsaW51eC1t bSxha3BtLG1hcmsucnV0bGFuZCxjYXRhbGluLm1hcmluYXMsbWhvY2tvLGhhbmp1bi5ndW8NCsqx vOSjujIwMTgtMDItMjEgMTk6NTg6MTUNCtb3zOI6UmU6ILTwuLQ6IFtSRkMgcGF0Y2hdIGlvcmVt YXA6IGRvbid0IHNldCB1cCBodWdlIEkvTyBtYXBwaW5ncyB3aGVuIHA0ZC9wdWQvcG1kIGlzIHpl cm8NCg0KW3NvcnJ5LCB0cnlpbmcgdG8gZGVhbCB3aXRoIHRvcC1wb3N0aW5nIGhlcmVdDQoNCk9u IFdlZCwgRmViIDIxLCAyMDE4IGF0IDA3OjM2OjM0QU0gKzAwMDAsIFdhbmd4dWVmZW5nIChFKSB3 cm90ZToNCj4gICAgICBUaGUgb2xkIGZsb3cgb2YgcmV1c2UgdGhlIDRrIHBhZ2UgYXMgMk0gcGFn ZSBkb2VzIG5vdCBmb2xsb3cgdGhlIEJCTSBmbG93DQo+IGZvciBwYWdlIHRhYmxlIHJlY29uc3Ry dWN0aW9uo6xub3Qgb25seSB0aGUgbWVtb3J5IGxlYWsgcHJvYmxlbXMuICBJZiBCQk0gZmxvdw0K PiBpcyBub3QgZm9sbG93ZWSjrHRoZSBzcGVjdWxhdGl2ZSBwcmVmZXRjaCBvZiB0bGIgd2lsbCBt YWRlIGZhbHNlIHRsYiBlbnRyaWVzDQo+IGNhY2hlZCBpbiBNTVUsIHRoZSBmYWxzZSBhZGRyZXNz IHdpbGwgYmUgZ290o6wgcGFuaWMgd2lsbCBoYXBwZW4uDQoNCklmIEkgdW5kZXJzdGFuZCBUb3No aSdzIHN1Z2dlc3Rpb24gY29ycmVjdGx5LCBoZSdzIHNheWluZyB0aGF0IHRoZSBQTUQgY2FuDQpi ZSBjbGVhcmVkIHdoZW4gdW5tYXBwaW5nIHRoZSBsYXN0IFBURSAobGlrZSB0cnlfdG9fZnJlZV9w dGVfcGFnZSkuIEluIHRoaXMNCmNhc2UsIHRoZXJlJ3Mgbm8gaXNzdWUgd2l0aCB0aGUgVExCIGJl Y2F1c2UgdGhpcyBpcyBleGFjdGx5IEJCTSAtLSB0aGUgUE1EDQppcyBjbGVhcmVkIGFuZCBUTEIg aW52YWxpZGF0aW9uIGlzIGlzc3VlZCBiZWZvcmUgdGhlIFBURSB0YWJsZSBpcyBmcmVlZC4gQQ0K c3Vic2VxdWVudCAyTSBtYXAgcmVxdWVzdCB3aWxsIHNlZSBhbiBlbXB0eSBQTUQgYW5kIHB1dCBk b3duIGEgYmxvY2sNCm1hcHBpbmcuDQoNClRoZSBkb3duc2lkZSBpcyB0aGF0IGZyZWVpbmcgYmVj b21lcyBtb3JlIGV4cGVuc2l2ZSBhcyB0aGUgbGFzdCBsZXZlbCB0YWJsZQ0KYmVjb21lcyBtb3Jl IHNwYXJzZWx5IHBvcHVsYXRlZCBhbmQgeW91IG5lZWQgdG8gZW5zdXJlIHlvdSBkb24ndCBoYXZl IGFueQ0KY29uY3VycmVudCBtYXBzIGdvaW5nIG9uIGZvciB0aGUgc2FtZSB0YWJsZSB3aGVuIHlv dSdyZSB1bm1hcHBpbmcuIEkgYWxzbw0KY2FuJ3Qgc2VlIGEgbmVhdCB3YXkgdG8gZml0IHRoaXMg aW50byB0aGUgY3VycmVudCB2dW5tYXAgY29kZS4gUGVyaGFwcyB3ZQ0KbmVlZCBhbiBpb3VubWFw X3BhZ2VfcmFuZ2UuDQoNCkluIHRoZSBtZWFudGltZSwgdGhlIGNvZGUgaW4gbGliL2lvcmVtYXAu YyBsb29rcyB0b3RhbGx5IGJyb2tlbiBzbyBJIHRoaW5rDQp3ZSBzaG91bGQgZGVzZWxlY3QgQ09O RklHX0hBVkVfQVJDSF9IVUdFX1ZNQVAgb24gYXJtNjQgdW50aWwgaXQncyBmaXhlZC4NCg0KV2ls bA0K --_000_etPan5a8d6a4e278c448b3d0elocalhost_ Content-Type: text/html; charset="gb2312" Content-Transfer-Encoding: quoted-printable
Hi, Will
       Thanks for your explain. If pmd cleare= d means making the pmd an invalid entry=A3=ACthat=A1=AF s no problem.
Thanks
       Wangxuefeng

Sent from HUAWEI AnyOffice
=B7=A2=BC=FE=C8=CB=A3=BAwill.dea= con
=CA=D5=BC=FE=C8=CB=A3=BA
=B3=AD=CB=CD=A3=BAtoshi.kani,lin= ux-arm-kernel,cpandya,linux-kernel,=B9=F9=BA=AE=BE=FC,Linuxarm,linux-mm,akp= m,mark.rutland,catalin.marinas,mhocko,hanjun.guo
=CA=B1=BC=E4=A3=BA2018-02-21 19:= 58:15
=D6=F7=CC=E2:Re: =B4=F0=B8=B4: [= RFC patch] ioremap: don't set up huge I/O mappings when p4d/pud/pmd is zero=

[sorry, trying to deal with top-posting here]

On Wed, Feb 21, 2018 at 07:36:34AM +0000, Wangxuefeng (E) wrote:
>      The old flow of reuse the 4k page as 2M = page does not follow the BBM flow
> for page table reconstruction=A3=ACnot only the memory leak problems.&= nbsp; If BBM flow
> is not followed=A3=ACthe speculative prefetch of tlb will made false t= lb entries
> cached in MMU, the false address will be got=A3=AC panic will happen.<= br>
If I understand Toshi's suggestion correctly, he's saying that the PMD can<= br> be cleared when unmapping the last PTE (like try_to_free_pte_page). In this=
case, there's no issue with the TLB because this is exactly BBM -- the PMD<= br> is cleared and TLB invalidation is issued before the PTE table is freed. A<= br> subsequent 2M map request will see an empty PMD and put down a block
mapping.

The downside is that freeing becomes more expensive as the last level table=
becomes more sparsely populated and you need to ensure you don't have any concurrent maps going on for the same table when you're unmapping. I also can't see a neat way to fit this into the current vunmap code. Perhaps we need an iounmap_page_range.

In the meantime, the code in lib/ioremap.c looks totally broken so I think<= br> we should deselect CONFIG_HAVE_ARCH_HUGE_VMAP on arm64 until it's fixed.
Will
 --_000_etPan5a8d6a4e278c448b3d0elocalhost_-- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org