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Mon, 24 Mar 2025 18:23:41 -0700 (PDT) X-Google-Smtp-Source: AGHT+IH/JUKTQmyT7rmzB1113MDJsVnMSnwa5fEmJ4QQvGW8nT/qrXson+JpXQKKM8geQr7VEFqwbzNfblKLM2iKFAI= X-Received: by 2002:a05:6e02:349c:b0:3d3:dd60:bc37 with SMTP id e9e14a558f8ab-3d5961c530dmr173136965ab.22.1742865820779; Mon, 24 Mar 2025 18:23:40 -0700 (PDT) MIME-Version: 1.0 References: <20250320015551.2157511-1-changyuanl@google.com> <20250320015551.2157511-12-changyuanl@google.com> In-Reply-To: From: Dave Young Date: Tue, 25 Mar 2025 09:24:02 +0800 X-Gm-Features: AQ5f1JqwitaQjBg4ofN5mWtcdKnJXVa6ylkj6L0R0h_oYxt_kysMu1ZOpV0VfzE Message-ID: Subject: Re: [PATCH v5 11/16] kexec: add config option for KHO To: Pasha Tatashin Cc: Changyuan Lyu , linux-kernel@vger.kernel.org, graf@amazon.com, akpm@linux-foundation.org, luto@kernel.org, anthony.yznaga@oracle.com, arnd@arndb.de, ashish.kalra@amd.com, benh@kernel.crashing.org, bp@alien8.de, catalin.marinas@arm.com, dave.hansen@linux.intel.com, dwmw2@infradead.org, ebiederm@xmission.com, mingo@redhat.com, jgowans@amazon.com, corbet@lwn.net, krzk@kernel.org, rppt@kernel.org, mark.rutland@arm.com, pbonzini@redhat.com, hpa@zytor.com, peterz@infradead.org, ptyadav@amazon.de, robh+dt@kernel.org, robh@kernel.org, saravanak@google.com, skinsburskii@linux.microsoft.com, rostedt@goodmis.org, tglx@linutronix.de, thomas.lendacky@amd.com, usama.arif@bytedance.com, will@kernel.org, devicetree@vger.kernel.org, kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: AK9iSHFUPOPlgiH8He4q3l2CuUNcv80w3a-Ne1kOygQ_1742865821 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: C92B01C0003 X-Stat-Signature: jzmhmjt6hhxewuyuacgchrsywx9z7rmd X-Rspam-User: X-HE-Tag: 1742865825-154083 X-HE-Meta: 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 qYOVaTY3 smdRXj5WZu//TGf5sk2qywBJjfekW0VZlChFAGfIugsr4u4dxwO1LIcNEeFKZ8AqGBULhnujaqtUlUi880iPB1d8J4TJOZ1AgiWxCWnVagCpFr5cS6GmR3Vs3BtbN/U1ES2zj7tBjtOqbsVtcu0NNDzwDA21C7eUQaqELub4GVCY7WqOG0va/fykAmL/fR4bd6z7o1QG5hc7t5gYgKz8ev+Rd+F+X5wuiQ7cSwRso+SFvL3TojYqoG36kD1qokARmWunKtVO16TyGTsXDMAOqqjnbPhfvItSE9N0RGE/UWdho5b+LBWZ9/WzpzHOP9ThnzdEGsTFGG5dLd/qg+cwaHhFJ/IiHIwhqELdVOD3zjQtmmUD7BXRDg4vtuQElkdzIFyuhGWKMrnV/sigT/ftnBZXxUhAEASd/BBdWA74zRdRrcU1A+RhHviP5bZaA96DyvvD1A7eQCh/uVMkDPqwoyzl8NgJy2MMtFIi6ULMPa7kFTkLfs7HZGuHRk36DqGVY3GiMPndh2oXSZwcdp04/N4gDvySLlNVbM2ahsduEVDMd4olnD8uNU8oFQe1s8EwJsq4Hbc/3ySNiWirS11zX6SH/1mM526gESBCfSEkXeD9JHhzVzFQaQBPD3JSO4ZlBlsrp99XjXGdVI8JCySkotrxIWgLbUnn6EC+zphfEAllyQ8jj4dgPEbxJw/5VN71rQVKH X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 25 Mar 2025 at 03:27, Pasha Tatashin wr= ote: > > On Mon, Mar 24, 2025 at 12:18=E2=80=AFAM Dave Young w= rote: > > > > On Thu, 20 Mar 2025 at 23:05, Changyuan Lyu wro= te: > > > > > > From: Alexander Graf > > > > > > We have all generic code in place now to support Kexec with KHO. This > > > patch adds a config option that depends on architecture support to > > > enable KHO support. > > > > > > Signed-off-by: Alexander Graf > > > Co-developed-by: Mike Rapoport (Microsoft) > > > Signed-off-by: Mike Rapoport (Microsoft) > > > Co-developed-by: Changyuan Lyu > > > Signed-off-by: Changyuan Lyu > > > --- > > > kernel/Kconfig.kexec | 15 +++++++++++++++ > > > 1 file changed, 15 insertions(+) > > > > > > diff --git a/kernel/Kconfig.kexec b/kernel/Kconfig.kexec > > > index 4d111f871951..57db99e758a8 100644 > > > --- a/kernel/Kconfig.kexec > > > +++ b/kernel/Kconfig.kexec > > > @@ -95,6 +95,21 @@ config KEXEC_JUMP > > > Jump between original kernel and kexeced kernel and invoke > > > code in physical address mode via KEXEC > > > > > > +config KEXEC_HANDOVER > > > + bool "kexec handover" > > > + depends on ARCH_SUPPORTS_KEXEC_HANDOVER && ARCH_SUPPORTS_KEXE= C_FILE > > > + select MEMBLOCK_KHO_SCRATCH > > > + select KEXEC_FILE > > > + select DEBUG_FS > > > + select LIBFDT > > > + select CMA > > > + select XXHASH > > > + help > > > + Allow kexec to hand over state across kernels by generating= and > > > + passing additional metadata to the target kernel. This is u= seful > > > + to keep data or state alive across the kexec. For this to w= ork, > > > + both source and target kernels need to have this option ena= bled. > > > + > > > > Have you tested kdump? In my mind there are two issues, one is with > > CMA enabled, it could cause kdump crashkernel memory reservation > > failures more often due to the fragmented low memory. Secondly, in > > As I understand cma low memory scratch reservation is needed only to > support some legacy pci devices that cannot use the full 64-bit space. > If so, I am not sure if KHO needs to be supported on machines with > such devices. However, even if we keep it, it should really be small, > so I would not expect that to be a problem for crash kernel memory > reservation. It is not easy to estimate how much of the KHO reserved memory is needed. I assume this as a mechanism for all different users, it is not predictable. Also it is not only about the size, but also it makes the memory fragmented. > > > kdump kernel dump the crazy scratch memory in vmcore is not very > > meaningful. Otherwise I suspect this is not tested under kdump. If > > so please disable this option for kdump. > > The scratch memory will appear as regular CMA in the vmcore. The crash > kernel can be kexec loaded only from userland, long after the scratch > memory is converted to CMA. Depending on the reserved size, if big enough it should be excluded in vmcore dumping. Otherwise if it is a kdump kernel it should skip the handling of the KHO passed previous old states. > > Pasha >