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Tue, 27 Oct 2026 01:02:20 -0700 (PDT) Date: Tue, 27 Oct 2026 09:02:14 +0100 From: Jiri Pirko To: Yeoreum Yun Cc: linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, jgg@ziepe.ca, david.quigley@intel.com, lukas@wunner.de, ksinyuk@kernel.org, rodrigo.vivi@intel.com, cedric.xing@intel.com, sameo@meta.com, drdeeglaze@gmail.com, James.Bottomley@hansenpartnership.com, aik@amd.com, jpiotrowski@nvidia.com, qinkun@google.com, pgonda@google.com, jic23@kernel.org, alistair.francis@wdc.com, ankita@nvidia.com, suzuki.poulose@arm.com, kas@kernel.org, rick.p.edgecombe@intel.com, elena.reshetova@intel.com, dave.hansen@linux.intel.com, sathyanarayanan.kuppuswamy@linux.intel.com, peter.fang@intel.com Subject: Re: [PATCH RFC 02/20] ctlv: Add the UAPI wire format and family API Message-ID: References: <20261015145053.3664509-1-jiri@resnulli.us> <20261015145053.3664509-3-jiri@resnulli.us> X-Mailing-List: kvm@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Mon, Oct 26, 2026 at 07:55:12PM +0100, yeoreum.yun@arm.com wrote: >Hi, > >> From: Jiri Pirko [..] >> +#define CTLV_MAX_NEST_DEPTH 32 > >JFYI, when I tested with CTLV_MAX_NEST_DEPTH as 32 and try to run >ctlv_msg_test_as_deep_as_the_core_allows() message_kunit.c test, >It experiences the *real stack overflow* on FVP >(lesser value (e.g. 16) is fine): > >[ 3.834419] ok 22 ctlv_msg_test_the_bit_where_it_means_nothing >[ 3.836499] ok 23 ctlv_msg_test_a_bit_no_version_declares >[ 3.837852] Insufficient stack space to handle exception! >[ 3.837875] ESR: 0x0000000096000047 -- DABT (current EL) >[ 3.837916] FAR: 0xffff800084efffe0 >[ 3.837953] Task stack: [0xffff800084f00000..0xffff800084f04000] >[ 3.838001] IRQ stack: [0xffff800083d50000..0xffff800083d54000] >[ 3.838049] Overflow stack: [0xffff00087b7c3150..0xffff00087b7c4150] >[ 3.838114] CPU: 7 UID: 0 PID: 257 Comm: kunit_try_catch Tainted: G N >** replaying previous printk message ** >[ 3.838114] CPU: 7 UID: 0 PID: 257 Comm: kunit_try_catch Tainted: G N 7.3.0-rc4+ #1216 PREEMPTLAZY >[ 3.838219] Tainted: [N]=TEST >[ 3.838249] Hardware name: , BIOS >[ 3.838279] pstate: 21400009 (nzCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--) >[ 3.838360] pc : __kmalloc_flags_noprof+0x10/0x540 >[ 3.838433] lr : __alloc_empty_sheaf+0x48/0x88 >[ 3.838501] sp : ffff800084efffa0 >[ 3.838534] x29: ffff800084f00030 x28: 0000000000000400 x27: 0000000000000400 >[ 3.838657] x26: ffff000803d721c0 x25: 0000000000000000 x24: 0000000000400cc0 >[ 3.838780] x23: ffff00087b7e3398 x22: 16e0800080564b98 x21: ffff0008000a0900 >[ 3.838908] x20: 0000000000000000 x19: ffff000800013600 x18: 0000000000000000 >[ 3.839029] x17: 0000000000000001 x16: 0000000000000002 x15: ffffffff00000001 >[ 3.839150] x14: 0000001c000001c0 x13: ffffffff00000001 x12: ffff000800013500 >[ 3.839275] x11: ffff00080370a800 x10: 0000000000000060 x9 : ffff8000805627d0 >[ 3.839401] x8 : 0000000000000000 x7 : ffffffff00000001 x6 : 0000001d000001d0 >[ 3.839521] x5 : ffff800080567b68 x4 : 00000000ffffffff x3 : 0000000000000004 >[ 3.839640] x2 : 0000000000000dc0 x1 : 0000000000000008 x0 : 0000000000000080 >[ 3.839761] Kernel panic - not syncing: kernel stack overflow >[ 3.841533] CPU: 7 UID: 0 PID: 257 Comm: kunit_try_catch Tainted: G N 7.3.0-rc4+ #1216 PREEMPTLAZY >[ 3.841783] Tainted: [N]=TEST >[ 3.841877] Hardware name: , BIOS >[ 3.841980] Call trace: >[ 3.842065] show_stack+0x20/0x40 (C) >[ 3.842246] __dump_stack+0x28/0x48 >[ 3.842427] dump_stack_lvl+0x28/0xb0 >[ 3.842609] dump_stack+0x18/0x34 >[ 3.842788] vpanic+0x208/0x5b8 >[ 3.842944] panic+0x54/0x60 >[ 3.843096] nmi_panic+0xc0/0xc8 >[ 3.843273] panic_bad_stack+0x10c/0x128 >[ 3.843466] handle_bad_stack+0x34/0x38 >[ 3.843622] __bad_stack+0x98/0xa0 >[ 3.843773] __kmalloc_flags_noprof+0x10/0x540 (P) >[ 3.843950] __pcs_replace_empty_main+0x2ac/0x3e8 >[ 3.844139] __kmalloc_node_track_caller_noprof+0x440/0x520 >[ 3.844328] krealloc_node_align_noprof+0x178/0x390 >[ 3.844509] kvrealloc_node_align_noprof+0x98/0x130 >[ 3.844690] ctlv_schema_index_scope_add+0xb0/0x3f8 >[ 3.844882] ctlv_schema_check_indexed_nest+0x1e8/0x958 > >(repeat ctlv_schema_check_attr()/ctlv_schema_check_indexed_nest()) > >[ 3.856919] ctlv_schema_check_attr+0x3dc/0x538 >[ 3.857105] ctlv_schema_check_indexed_nest+0x788/0x958 >[ 3.857301] ctlv_schema_validate+0x88/0x180 >[ 3.857482] ctlv_msg_test_as_deep_as_the_core_allows+0x11c/0x1e8 >[ 3.857698] kunit_try_run_case+0x64/0x188 >[ 3.857878] kunit_generic_run_threadfn_adapter+0x30/0x68 >[ 3.858086] kthread+0x10c/0x140 >[ 3.858245] ret_from_fork+0x10/0x20 >[ 3.858398] SMP: stopping secondary CPUs >[ 3.858630] Kernel Offset: disabled >[ 3.858720] CPU features: 0x0,00000000,00b0802e,9f190bc3,2affe72f >[ 3.858872] Memory Limit: none >[ 3.858976] ---[ end Kernel panic - not syncing: kernel stack overflow ]--- > >[...] > >I think it might be good to configurable according to architecture >unless it's not good to reduce the CTLV_MAX_NEST_DEPTH number >otherwise, increasing stack size when CTLV is enabled seems unresonable... Agreed, will lower it down. I think we should be okay with 8 for start.