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Thu, 08 Jan 2026 08:41:22 -0800 (PST) From: Breno Leitao Date: Thu, 08 Jan 2026 08:40:59 -0800 Subject: [PATCH v3 2/2] kho: history: track kexec boot counter MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260108-kho-v3-2-b1d6b7a89342@debian.org> References: <20260108-kho-v3-0-b1d6b7a89342@debian.org> In-Reply-To: <20260108-kho-v3-0-b1d6b7a89342@debian.org> To: Alexander Graf , Mike Rapoport , Pasha Tatashin , Pratyush Yadav Cc: linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-mm@kvack.org, usamaarif642@gmail.com, rmikey@meta.com, clm@fb.com, riel@surriel.com, Breno Leitao , kernel-team@meta.com X-Mailer: b4 0.15-dev-47773 X-Developer-Signature: v=1; a=openpgp-sha256; l=3603; i=leitao@debian.org; h=from:subject:message-id; bh=EGjW1NDVm9NCUZnt/TocKG3VnYx6DZQuPLEer3uoR8g=; b=owEBbQKS/ZANAwAIATWjk5/8eHdtAcsmYgBpX94vFhyv1+q5nq7d3U4aG09l2a2v9OVLjM38M Alw0viiRZ2JAjMEAAEIAB0WIQSshTmm6PRnAspKQ5s1o5Of/Hh3bQUCaV/eLwAKCRA1o5Of/Hh3 bYQwD/9eHb6ErCrxXzsTuDNHlKgULxd03DOyrKRfmQu7kTOUtZlqSCyZ4P2EeLCfbluUpJnnESG UAVFWIxNs7YXzhUNd7cWqmoZH+mBLVOby7T8HD+MeG+8z6VuUQXpE9mQVEsS0N5g0L6+FWWFgAd VqezYtxXpJeV32vXCpcmBEcZpUE3od+8MAIK1LqWcUbsCKLy/0kXXemulGMzLks31aLqX86ni/i X+9lZpg99/gVXF8Jz3lqX+hNi9TIRsXWGaU281XTD1tF3BgTcXXCyHE8m15DjbelamQimU3chBg DMteI6JOK4sjOWjTLtutUHeHuUwcuuUpiTc2Zk+pvF6X4ij24/VQcoCVl9QLiHL4EjTlbYaXGMK eh6yLVMjs32YEVhnOxY850v6dWpXovo5PFQUd3ECljjlvTmrD6aLrQh1g92CX7sPIoJYTOEIl8x 81RtpCzW+Gky6ezAfpzbZfnGAJrQi2XvgB6Y7xvZEiDsGTKtnNKeHZ4uZDf2xt0EBZmbk8aP4Rd IQ/tPzLyEsBSAJTjlPDAIaeEFRFmBwoI1s/vu1zCB0DiRnm6/tnremV8GX/ewBSbiyaDWX2+8zH AzQ0hXXhX98UteCdW/+vC7v/59qftT+spmlGWRF8WqkY9v/ZZwZ3kMESQjBGioYQXj3Q3+SR7BB FQswweva+CDz0Zg== X-Developer-Key: i=leitao@debian.org; a=openpgp; fpr=AC8539A6E8F46702CA4A439B35A3939FFC78776D X-Rspam-User: X-Stat-Signature: zrd41sumtjaxjg9x95pk9fht1qkmx8qf X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: DC57A80010 X-HE-Tag: 1767890483-664629 X-HE-Meta: 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 MJNEYzAl tBRwDEgf6IdsMVkmUjcEtvxHdXzlco/6fMJ9UKR6NEXUw8KxTCPDhactK/WteO0cAAsuD9NvpkG7yPC9hLUdRpXy0MeZ8uZRr3+S4gOit2/Gz5zFou59gyCnJ+AGPRpWbQsqAR0GA/193m7hTT12veH4037fECC+SdLOHJJxkFbZl0f/TxJHh79b3Ynmge2Y0tOQr1SeasVV1lCPsDyViy5AcAUboj3gRbDBPwMMJ/zfuK7C0hMRQ1cQ7QYtMGbJttLrYpxSzHAQeX3rgKxmdYDDA3XtNRGSW5XhtP+vAvmrzEPcdGIoC++mkSogzp/NeD+hthdg2EWaXugoW6Y3yn90UtFB8sugMXONjXiAZRvAjxle1FSpH6GR/87ZB/ymbPGQABkOJ/kE74xjYSGx1T0pEIrKEXTF3bGh3qoa/YirkR5ty4ocDh/5ZTg== 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: Track and display the number of kexec boots since the last cold reboot. This extends the previous kernel release tracking by adding a counter that increments with each kexec boot. The counter provides visibility into the kexec chain depth, which is useful for understanding boot history in production environments. Add a new property "kexec-count" in KHO FDT alongside the existing "previous-release" property. The counter is: - Initialized to 0 on cold boot (when kho_in is first instantiated) - Incremented by 1 on each subsequent kexec - Printed alongside the previous kernel release version The counter is stored as a 32-bit unsigned integer in FDT format. This is different than counter for LUO, given KHO can be used independently from LUO. Also WARN() if KHO_PROP_PREVIOUS_RELEASE doesn't exist, because it must exist if KHO_PROP_PREVIOUS_RELEASE exists. Signed-off-by: Breno Leitao Suggested-by: Pasha Tatashin --- include/linux/kho/abi/kexec_handover.h | 3 +++ kernel/liveupdate/kexec_handover.c | 16 +++++++++++++++- 2 files changed, 18 insertions(+), 1 deletion(-) diff --git a/include/linux/kho/abi/kexec_handover.h b/include/linux/kho/abi/kexec_handover.h index f4f31e8f575b..9c4fc4c6a212 100644 --- a/include/linux/kho/abi/kexec_handover.h +++ b/include/linux/kho/abi/kexec_handover.h @@ -87,6 +87,9 @@ /* The FDT property to track previous kernel (kexec caller) */ #define KHO_PROP_PREVIOUS_RELEASE "previous-release" +/* The FDT property to track number of kexec counts so far */ +#define KHO_PROP_KEXEC_COUNT "kexec-count" + /** * DOC: Kexec Handover ABI for vmalloc Preservation * diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c index b2d57868d22f..34cfc98076b8 100644 --- a/kernel/liveupdate/kexec_handover.c +++ b/kernel/liveupdate/kexec_handover.c @@ -1248,6 +1248,7 @@ struct kho_in { phys_addr_t scratch_phys; phys_addr_t mem_map_phys; char previous_release[__NEW_UTS_LEN + 1]; + u32 kexec_count; struct kho_debugfs dbg; }; @@ -1319,6 +1320,7 @@ static __init int kho_out_fdt_setup(void) { void *root = kho_out.fdt; u64 empty_mem_map = 0; + u32 kexec_count; int err; err = fdt_create(root, PAGE_SIZE); @@ -1329,6 +1331,10 @@ static __init int kho_out_fdt_setup(void) sizeof(empty_mem_map)); err |= fdt_property_string(root, KHO_PROP_PREVIOUS_RELEASE, init_uts_ns.name.release); + /* kho_in.kexec_count is set to 0 on cold boot */ + kexec_count = kho_in.kexec_count + 1; + err |= fdt_property(root, KHO_PROP_KEXEC_COUNT, &kexec_count, + sizeof(kexec_count)); err |= fdt_end_node(root); err |= fdt_finish(root); @@ -1443,15 +1449,23 @@ void __init kho_memory_init(void) static int __init kho_print_previous_kernel(const void *fdt) { const char *prev_release; + const u32 *count_ptr; int len; prev_release = fdt_getprop(fdt, 0, KHO_PROP_PREVIOUS_RELEASE, &len); if (!prev_release || len <= 0) return -ENOENT; + /* Read the kexec count from the previous kernel */ + count_ptr = fdt_getprop(fdt, 0, KHO_PROP_KEXEC_COUNT, &len); + if (WARN_ON(!count_ptr || len != sizeof(u32))) + return -ENOENT; + kho_in.kexec_count = *count_ptr; + strscpy(kho_in.previous_release, prev_release, sizeof(kho_in.previous_release)); - pr_info("exec from: %s\n", kho_in.previous_release); + pr_info("exec from: %s (count %u)\n", kho_in.previous_release, + kho_in.kexec_count); return 0; } -- 2.47.3