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([2001:16a2:c8d2:2b00:183a:1350:d3a4:d89]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4324ea82feasm85809097f8f.24.2026.01.02.07.02.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 02 Jan 2026 07:02:42 -0800 (PST) Message-ID: <2b315095-2393-45d5-b0bf-ea9fbecd2607@gmail.com> Date: Fri, 2 Jan 2026 18:02:39 +0300 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] kexec: history: track previous kernel version To: Breno Leitao , Alexander Graf , Mike Rapoport , Pasha Tatashin , Pratyush Yadav Cc: linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-mm@kvack.org, rmikey@meta.com, clm@fb.com, riel@surriel.com, kernel-team@meta.com References: <20260102-kho-v2-0-1747b1a3a1d6@debian.org> <20260102-kho-v2-1-1747b1a3a1d6@debian.org> Content-Language: en-GB From: Usama Arif In-Reply-To: <20260102-kho-v2-1-1747b1a3a1d6@debian.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 02/01/2026 17:53, Breno Leitao wrote: > Add CONFIG_KEXEC_HISTORY to store and display the kernel version from > the previous kexec boot. > > When enabled, the current kernel's release string is saved to the > "previous-release" property in the KHO device tree before kexec. On > the next boot, if this property exists, the previous kernel version > is retrieved and printed during early boot. > > This helps diagnose bugs that only manifest when kexecing from > specific kernel versions, making it easier to correlate crashes with > the kernel that initiated the kexec. > > Disabled by default to avoid overhead for users who don't need this > information. > > Signed-off-by: Breno Leitao > --- > kernel/Kconfig.kexec | 13 +++++++++++++ > kernel/liveupdate/kexec_handover.c | 29 +++++++++++++++++++++++++++++ > 2 files changed, 42 insertions(+) > > diff --git a/kernel/Kconfig.kexec b/kernel/Kconfig.kexec > index 15632358bcf7..b770c68a3800 100644 > --- a/kernel/Kconfig.kexec > +++ b/kernel/Kconfig.kexec > @@ -94,6 +94,19 @@ config KEXEC_JUMP > Jump between original kernel and kexeced kernel and invoke > code in physical address mode via KEXEC > > +config KEXEC_HISTORY > + bool "Track kexec kernel history" > + depends on KEXEC_HANDOVER > + help > + When enabled, the kernel will store its release version in the > + KHO FDT before kexec, and the newly booted kernel will read and > + print this information during early boot. > + > + This is useful for debugging and auditing to know which kernel > + version performed the kexec that booted the current kernel. > + > + If unsure, say N. > + I think we should make this default if KHO is enabled, i.e. not have a Kconfig option for this. The cost of storing the char array is negligable. > config CRASH_DUMP > bool "kernel crash dumps" > default ARCH_DEFAULT_CRASH_DUMP > diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c > index 73da00aeaa99..06d99627bb3c 100644 > --- a/kernel/liveupdate/kexec_handover.c > +++ b/kernel/liveupdate/kexec_handover.c > @@ -21,6 +21,7 @@ > #include > #include > #include > +#include > > #include > > @@ -36,6 +37,7 @@ > #define KHO_FDT_COMPATIBLE "kho-v1" > #define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map" > #define PROP_SUB_FDT "fdt" > +#define PROP_PREVIOUS_RELEASE "previous-release" > > #define KHO_PAGE_MAGIC 0x4b484f50U /* ASCII for 'KHOP' */ > > @@ -1253,6 +1255,9 @@ bool kho_finalized(void) > struct kho_in { > phys_addr_t fdt_phys; > phys_addr_t scratch_phys; > +#ifdef CONFIG_KEXEC_HISTORY > + char previous_release[__NEW_UTS_LEN + 1]; > +#endif > struct kho_debugfs dbg; > }; > > @@ -1332,6 +1337,10 @@ static __init int kho_out_fdt_setup(void) > err |= fdt_property_string(root, "compatible", KHO_FDT_COMPATIBLE); > err |= fdt_property(root, PROP_PRESERVED_MEMORY_MAP, &empty_mem_map, > sizeof(empty_mem_map)); > +#ifdef CONFIG_KEXEC_HISTORY > + err |= fdt_property_string(root, PROP_PREVIOUS_RELEASE, > + init_uts_ns.name.release); > +#endif > err |= fdt_end_node(root); > err |= fdt_finish(root); > > @@ -1455,6 +1464,25 @@ void __init kho_memory_init(void) > } > } > > +#ifdef CONFIG_KEXEC_HISTORY > +static void __init kho_print_previous_kernel(const void *fdt) > +{ > + const char *prev_release; > + int len; > + > + prev_release = fdt_getprop(fdt, 0, PROP_PREVIOUS_RELEASE, &len); > + if (!prev_release || len <= 0) > + return; > + > + strscpy(kho_in.previous_release, prev_release, > + sizeof(kho_in.previous_release)); > + pr_info("This kernel was kexec'ed from kernel release: %s\n", > + kho_in.previous_release); Maybe s/release/version everywhere? It might not be a release, but no strong opinion. > +} > +#else > +static void __init kho_print_previous_kernel(const void *fdt) { } > +#endif > + > void __init kho_populate(phys_addr_t fdt_phys, u64 fdt_len, > phys_addr_t scratch_phys, u64 scratch_len) > { > @@ -1527,6 +1555,7 @@ void __init kho_populate(phys_addr_t fdt_phys, u64 fdt_len, > kho_in.scratch_phys = scratch_phys; > kho_scratch_cnt = scratch_cnt; > pr_info("found kexec handover data.\n"); > + kho_print_previous_kernel(fdt); > > out: > if (fdt) >