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[79.27.108.198]) by smtp.gmail.com with ESMTPSA id q12-20020a056000136c00b0021e47fb24a2sm14511127wrz.19.2022.08.02.04.02.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Aug 2022 04:02:26 -0700 (PDT) From: "Fabio M. De Francesco" To: Baoquan He Cc: Eric Biederman , kexec@lists.infradead.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, Ira Weiny Subject: Re: [PATCH v2] kexec: Replace kmap() with kmap_local_page() Date: Tue, 02 Aug 2022 13:02:25 +0200 Message-ID: <5847084.alqRGMn8q6@opensuse> In-Reply-To: References: <20220707231550.1484-1-fmdefrancesco@gmail.com> <1923146.PYKUYFuaPT@opensuse> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220802_040231_490118_8679C0A3 X-CRM114-Status: GOOD ( 23.72 ) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org T24gbWFydGVkw6wgMiBhZ29zdG8gMjAyMiAwOTozMjo0NiBDRVNUIEJhb3F1YW4gSGUgd3JvdGU6 Cj4gT24gMDgvMDIvMjIgYXQgMDg6MjBhbSwgRmFiaW8gTS4gRGUgRnJhbmNlc2NvIHdyb3RlOgo+ ID4gT24gbWFydGVkw6wgMiBhZ29zdG8gMjAyMiAwNTowNjo1NCBDRVNUIEJhb3F1YW4gSGUgd3Jv dGU6Cj4gPiA+IE9uIDA3LzA4LzIyIGF0IDAxOjE1YW0sIEZhYmlvIE0uIERlIEZyYW5jZXNjbyB3 cm90ZToKPiA+ID4gPiBUaGUgdXNlIG9mIGttYXAoKSBhbmQga21hcF9hdG9taWMoKSBhcmUgYmVp bmcgZGVwcmVjYXRlZCBpbiBmYXZvciAKb2YKPiA+ID4gPiBrbWFwX2xvY2FsX3BhZ2UoKS4KPiA+ ID4gPiAKPiA+ID4gPiBXaXRoIGttYXBfbG9jYWxfcGFnZSgpLCB0aGUgbWFwcGluZ3MgYXJlIHBl ciB0aHJlYWQsIENQVSBsb2NhbCBhbmQgCm5vdAo+ID4gPiA+IGdsb2JhbGx5IHZpc2libGUuIEZ1 cnRoZXJtb3JlLCB0aGUgbWFwcGluZ3MgY2FuIGJlIGFjcXVpcmVkIGZyb20gCmFueQo+ID4gPiA+ IGNvbnRleHQgKGluY2x1ZGluZyBpbnRlcnJ1cHRzKS4KPiA+ID4gPiAKPiA+ID4gPiBUaGVyZWZv cmUsIHVzZSBrbWFwX2xvY2FsX3BhZ2UoKSBpbiBrZXhlY19jb3JlLmMgYmVjYXVzZSB0aGVzZSAK bWFwcGluZ3MgCj4gPiBhcmUKPiA+ID4gPiBwZXIgdGhyZWFkLCBDUFUgbG9jYWwsIGFuZCBub3Qg Z2xvYmFsbHkgdmlzaWJsZS4KPiA+ID4gPiAKPiA+ID4gPiBUZXN0ZWQgb24gYSBRRU1VICsgS1ZN IDMyLWJpdHMgVk0gYm9vdGluZyBhIGtlcm5lbCB3aXRoIEhJR0hNRU02NEdCCj4gPiA+ID4gZW5h YmxlZC4KPiA+ID4gCj4gPiA+IFdvbmRlcmluZyB3aGF0IGFyY2ggeW91IHRlc3RlZCB3aXRoLgo+ ID4gCj4gPiBJJ20gc29ycnksIEkgZm9yZ290IHRvIHNheSB0aGF0IEkgdXNlIHg4Nl8zMiB3aXRo IDRHQiB0byA2R0IgUkFNLgo+ID4gVGhpcyBpcyB1c3VhbGx5IGFuIGluZm9ybWF0aW9uIHRoYXQg SSBhZGQgaW4gdGhlIGNvbW1pdCBtZXNzYWdlcyBvZiBhbGwgCnRoZSAKPiA+IHJlY2VudCBjb252 ZXJzaW9ucyBJJ20gd29ya2luZyBvbiBhY3Jvc3MgdGhlIGVudGlyZSBrZXJuZWwuCj4gPiAKPiA+ IEFub3RoZXIgaW1wb3J0YW50IGluZm9ybWF0aW9uIChvdmVybG9va2VkIGFnYWluIHRoaXMgdGlt ZSkgaXMgdGhhdCAoMSkgCj4gPiBrbWFwKCkgY29tZXMgd2l0aCBhbiBvdmVyaGVhZCBhcyBtYXBw aW5nIHNwYWNlIGlzIHJlc3RyaWN0ZWQgYW5kIApwcm90ZWN0ZWQgCj4gPiBieSBhIGdsb2JhbCBs b2NrIGZvciBzeW5jaHJvbml6YXRpb24gYW5kICgyKSBpdCBhbHNvIHJlcXVpcmVzIGdsb2JhbCAK VExCIAo+ID4gaW52YWxpZGF0aW9uIHdoZW4gdGhlIGttYXDigJlzIHBvb2wgd3JhcHMgYW5kIGl0 IG1pZ2h0IGJsb2NrIHdoZW4gdGhlIAptYXBwaW5nIAo+ID4gc3BhY2UgaXMgZnVsbHkgdXRpbGl6 ZWQgdW50aWwgYSBzbG90IGJlY29tZXMgYXZhaWxhYmxlLgo+IAo+IFRoYW5rcyBhIGxvdCBmb3Ig dXBkYXRlIHdpdGggbW9yZSBkZXRhaWxzLCBGYWJpby4KCllvdSdyZSB3ZWxjb21lLgoKPiBNYXli ZSB0aGVzZSBjYW4gYmUKPiBhZGRlZCBpbnRvIGxvZyB3aXRoIHYzIGlmIHlvdSB0aGluayB0aGV5 IGFyZSB3b3J0aCBhZGRpbmcsIGFuZCB3aXRoIG15Cj4gQWNrIHNpbmNlIG5vIGNvZGUgY2hhbmdl IHJlbGF0ZWQuIFlvdSBkZWNpZGUuCgpGb3Igd2Vla3MgSSd2ZSBiZWVuIHRoaW5raW5nIHRoYXQg dGhlc2UgZGV0YWlscyB3ZXJlIG5vdCBuZWNlc3NhcnkgaW4gdGhlIApjb21taXQgbWVzc2FnZSBv ZiB0aGVzZSBjb252ZXJzaW9ucy4gTGF0ZXIgSSByZWFsaXplZCB0aGF0IGEgZmFpciBudW1iZXIg b2YgCm1haW50YWluZXJzIHdlcmVuJ3QgYXdhcmUgb2Ygd2h5IHdlIHNob3VsZCBjaGFuZ2Ugc29t ZXRoaW5nIHRoYXQgaGFkIGJlZW4gCndvcmtpbmcgInByb3Blcmx5IiBmb3IgeWVhcnMuIFBlcmhh cHMgdGhleSB0aG91Z2h0IHRoYXQgd2Ugd291bGQgZmFjZSB0b28gCm1hbnkgcmlza3Mgb2YgYnJl YWtpbmcgdGhpbmdzIHZlcnN1cyBsaXR0bGUgcmV3YXJkcy4KCkFmdGVyIGRpc2N1c3Npbmcgd2l0 aCBHcmVnIEstSCAod2hvIHdhcyBpbml0aWFsbHkgbm90IGZvbmQgb2YgdGhlc2UgY2hhbmdlcyAK dG8gY29yZSBwYXJ0cyBvZiBmaXJtd2FyZSBsb2FkaW5nIG1lY2hhbmlzbSksIGhlIHN1Z2dlc3Rl ZCB0aGF0IGEgcHJvcGVyIApjb21taXQgbG9nIHdpdGggdGhlIG5lY2Vzc2FyeSBpbmZvcm1hdGlv biBjb3VsZCBoYXZlIGhlbHBlZCBoaW1zZWxmIGFuZCB0aGUgCm90aGVyIG1haW50YWluZXJzIHdo byBtYXkgbm90IHlldCBoYWQgdGltZSB0byBkZWVwZW4gdGhpcyB0b3BpY3MuCgpUaGlzIHBhdGNo IHRvICJrZXhlYyIgc2xpcHBlZCBpbiB3aXRoIG5vIHN1Y2ggYWRkaXRpb25zLgoKVGhlcmVmb3Jl LCBJIGFncmVlIHdpdGggeW91IGluIGZ1bGw6IEknbGwgYWRkIHRoZXNlIGluZm9ybWF0aW9uIGFu ZCBzZW5kIGEgCm5ldyB2ZXJzaW9uIEFTQVAuCgo+IFRoYW5rcyBhZ2FpbiBmb3IgdGhlIGVmZm9y dC4KClRoYW5rcyBzbyBtdWNoIGZvciB0aGUgIkFja2VkLWJ5OiIgdGFnIGZyb20geW91LgoKRmFi aW8gIAoKW3NuaXBdCgoKCl9fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fX19fCmtleGVjIG1haWxpbmcgbGlzdAprZXhlY0BsaXN0cy5pbmZyYWRlYWQub3JnCmh0dHA6 Ly9saXN0cy5pbmZyYWRlYWQub3JnL21haWxtYW4vbGlzdGluZm8va2V4ZWMK From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D8C8BC19F2C for ; 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[79.27.108.198]) by smtp.gmail.com with ESMTPSA id q12-20020a056000136c00b0021e47fb24a2sm14511127wrz.19.2022.08.02.04.02.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Aug 2022 04:02:26 -0700 (PDT) From: "Fabio M. De Francesco" To: Baoquan He Cc: Eric Biederman , kexec@lists.infradead.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, Ira Weiny Subject: Re: [PATCH v2] kexec: Replace kmap() with kmap_local_page() Date: Tue, 02 Aug 2022 13:02:25 +0200 Message-ID: <5847084.alqRGMn8q6@opensuse> In-Reply-To: References: <20220707231550.1484-1-fmdefrancesco@gmail.com> <1923146.PYKUYFuaPT@opensuse> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On marted=C3=AC 2 agosto 2022 09:32:46 CEST Baoquan He wrote: > On 08/02/22 at 08:20am, Fabio M. De Francesco wrote: > > On marted=C3=AC 2 agosto 2022 05:06:54 CEST Baoquan He wrote: > > > On 07/08/22 at 01:15am, Fabio M. De Francesco wrote: > > > > The use of kmap() and kmap_atomic() are being deprecated in favor=20 of > > > > kmap_local_page(). > > > >=20 > > > > With kmap_local_page(), the mappings are per thread, CPU local and= =20 not > > > > globally visible. Furthermore, the mappings can be acquired from=20 any > > > > context (including interrupts). > > > >=20 > > > > Therefore, use kmap_local_page() in kexec_core.c because these=20 mappings=20 > > are > > > > per thread, CPU local, and not globally visible. > > > >=20 > > > > Tested on a QEMU + KVM 32-bits VM booting a kernel with HIGHMEM64GB > > > > enabled. > > >=20 > > > Wondering what arch you tested with. > >=20 > > I'm sorry, I forgot to say that I use x86_32 with 4GB to 6GB RAM. > > This is usually an information that I add in the commit messages of all= =20 the=20 > > recent conversions I'm working on across the entire kernel. > >=20 > > Another important information (overlooked again this time) is that (1)= =20 > > kmap() comes with an overhead as mapping space is restricted and=20 protected=20 > > by a global lock for synchronization and (2) it also requires global=20 TLB=20 > > invalidation when the kmap=E2=80=99s pool wraps and it might block when= the=20 mapping=20 > > space is fully utilized until a slot becomes available. >=20 > Thanks a lot for update with more details, Fabio. You're welcome. > Maybe these can be > added into log with v3 if you think they are worth adding, and with my > Ack since no code change related. You decide. =46or weeks I've been thinking that these details were not necessary in the= =20 commit message of these conversions. Later I realized that a fair number of= =20 maintainers weren't aware of why we should change something that had been=20 working "properly" for years. Perhaps they thought that we would face too=20 many risks of breaking things versus little rewards. After discussing with Greg K-H (who was initially not fond of these changes= =20 to core parts of firmware loading mechanism), he suggested that a proper=20 commit log with the necessary information could have helped himself and the= =20 other maintainers who may not yet had time to deepen this topics. This patch to "kexec" slipped in with no such additions. Therefore, I agree with you in full: I'll add these information and send a= =20 new version ASAP. > Thanks again for the effort. Thanks so much for the "Acked-by:" tag from you. =46abio =20 [snip]