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smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=loongson.cn; spf=pass smtp.mailfrom=loongson.cn; arc=none smtp.client-ip=114.242.206.163 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=loongson.cn Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=loongson.cn Received: from loongson.cn (unknown [111.9.175.10]) by gateway (Coremail) with SMTP id _____8AxDMN2MVFptNMDAA--.11916S3; Sun, 28 Dec 2025 21:32:38 +0800 (CST) Received: from [10.136.12.26] (unknown [111.9.175.10]) by front1 (Coremail) with SMTP id qMiowJDxD8NuMVFpc9IFAA--.16475S3; Sun, 28 Dec 2025 21:32:34 +0800 (CST) Subject: Re: [PATCH V3 2/2] LoongArch: KVM: fix "unreliable stack" issue To: Xianglai Li , loongarch@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: stable@vger.kernel.org, Huacai Chen , WANG Xuerui , Tianrui Zhao , Bibo Mao , Charlie Jenkins , Thomas Gleixner , Tiezhu Yang References: <20251227012712.2921408-1-lixianglai@loongson.cn> <20251227012712.2921408-3-lixianglai@loongson.cn> From: Jinyang He Message-ID: <08143343-cb10-9376-e7df-68ad854b9275@loongson.cn> Date: Sun, 28 Dec 2025 21:32:30 +0800 User-Agent: Mozilla/5.0 (X11; Linux loongarch64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20251227012712.2921408-3-lixianglai@loongson.cn> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-CM-TRANSID:qMiowJDxD8NuMVFpc9IFAA--.16475S3 X-CM-SenderInfo: pkhmx0p1dqwqxorr0wxvrqhubq/ X-Coremail-Antispam: 1Uk129KBj93XoWxtw4rJw1xKryDKw4UJr1kWFX_yoWxGw1fpw nxAFs8Ka1kJa90vw47Ja4kArWaqrZ2gF1fWrsFvrWrAr1DWry5XF18tw4DZF97K3y8WFn5 XFyjgrn5AaykAagCm3ZEXasCq-sJn29KB7ZKAUJUUUU7529EdanIXcx71UUUUU7KY7ZEXa sCq-sGcSsGvfJ3Ic02F40EFcxC0VAKzVAqx4xG6I80ebIjqfuFe4nvWSU5nxnvy29KBjDU 0xBIdaVrnRJUUUBjb4IE77IF4wAFF20E14v26r1j6r4UM7CY07I20VC2zVCF04k26cxKx2 IYs7xG6rWj6s0DM7CIcVAFz4kK6r1Y6r17M28lY4IEw2IIxxk0rwA2F7IY1VAKz4vEj48v e4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Jr0_JF4l84ACjcxK6xIIjxv20xvEc7CjxVAFwI 0_Jr0_Gr1l84ACjcxK6I8E87Iv67AKxVW8JVWxJwA2z4x0Y4vEx4A2jsIEc7CjxVAFwI0_ Gr0_Gr1UM2kKe7AKxVWUXVWUAwAS0I0E0xvYzxvE52x082IY62kv0487Mc804VCY07AIYI kI8VC2zVCFFI0UMc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VC0I7IYx2IY67AKxVWUAVWU twAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFVCjc4AY6r1j6r4UM4x0Y48IcVAKI48JMx k0xIA0c2IEe2xFo4CEbIxvr21l42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_ Gr1l4IxYO2xFxVAFwI0_Jrv_JF1lx2IqxVAqx4xG67AKxVWUJVWUGwC20s026x8GjcxK67 AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1q6r43MIIYrxkI7VAKI48JMIIF0xvE2Ix0cI8I cVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I0E14v26r1j6r4UMIIF0xvE42xK8VAvwI 8IcIk0rVWUJVWUCwCI42IY6I8E87Iv67AKxVWUJVW8JwCI42IY6I8E87Iv6xkF7I0E14v2 6r1j6r4UYxBIdaVFxhVjvjDU0xZFpf9x07j5xhLUUUUU= On 2025-12-27 09:27, Xianglai Li wrote: > Insert the appropriate UNWIND macro definition into the kvm_exc_entry in > the assembly function to guide the generation of correct ORC table entries, > thereby solving the timeout problem of loading the livepatch-sample module > on a physical machine running multiple vcpus virtual machines. > > While solving the above problems, we have gained an additional benefit, > that is, we can obtain more call stack information > > Stack information that can be obtained before the problem is fixed: > [<0>] kvm_vcpu_block+0x88/0x120 [kvm] > [<0>] kvm_vcpu_halt+0x68/0x580 [kvm] > [<0>] kvm_emu_idle+0xd4/0xf0 [kvm] > [<0>] kvm_handle_gspr+0x7c/0x700 [kvm] > [<0>] kvm_handle_exit+0x160/0x270 [kvm] > [<0>] kvm_exc_entry+0x100/0x1e0 > > Stack information that can be obtained after the problem is fixed: > [<0>] kvm_vcpu_block+0x88/0x120 [kvm] > [<0>] kvm_vcpu_halt+0x68/0x580 [kvm] > [<0>] kvm_emu_idle+0xd4/0xf0 [kvm] > [<0>] kvm_handle_gspr+0x7c/0x700 [kvm] > [<0>] kvm_handle_exit+0x160/0x270 [kvm] > [<0>] kvm_exc_entry+0x104/0x1e4 > [<0>] kvm_enter_guest+0x38/0x11c > [<0>] kvm_arch_vcpu_ioctl_run+0x26c/0x498 [kvm] > [<0>] kvm_vcpu_ioctl+0x200/0xcf8 [kvm] > [<0>] sys_ioctl+0x498/0xf00 > [<0>] do_syscall+0x98/0x1d0 > [<0>] handle_syscall+0xb8/0x158 > > Cc: stable@vger.kernel.org > Signed-off-by: Xianglai Li > --- > Cc: Huacai Chen > Cc: WANG Xuerui > Cc: Tianrui Zhao > Cc: Bibo Mao > Cc: Charlie Jenkins > Cc: Xianglai Li > Cc: Thomas Gleixner > Cc: Tiezhu Yang > > arch/loongarch/kvm/switch.S | 28 +++++++++++++++++++--------- > 1 file changed, 19 insertions(+), 9 deletions(-) > > diff --git a/arch/loongarch/kvm/switch.S b/arch/loongarch/kvm/switch.S > index 93845ce53651..a3ea9567dbe5 100644 > --- a/arch/loongarch/kvm/switch.S > +++ b/arch/loongarch/kvm/switch.S > @@ -10,6 +10,7 @@ > #include > #include > #include > +#include > > #define HGPR_OFFSET(x) (PT_R0 + 8*x) > #define GGPR_OFFSET(x) (KVM_ARCH_GGPR + 8*x) > @@ -110,9 +111,9 @@ > * need to copy world switch code to DMW area. > */ > .text > + .p2align PAGE_SHIFT > .cfi_sections .debug_frame > SYM_CODE_START(kvm_exc_entry) > - .p2align PAGE_SHIFT > UNWIND_HINT_UNDEFINED > csrwr a2, KVM_TEMP_KS > csrrd a2, KVM_VCPU_KS > @@ -170,6 +171,7 @@ SYM_CODE_START(kvm_exc_entry) > /* restore per cpu register */ > ld.d u0, a2, KVM_ARCH_HPERCPU > addi.d sp, sp, -PT_SIZE > + UNWIND_HINT_REGS > > /* Prepare handle exception */ > or a0, s0, zero > @@ -200,7 +202,7 @@ ret_to_host: > jr ra > > SYM_CODE_END(kvm_exc_entry) > -EXPORT_SYMBOL(kvm_exc_entry) > +EXPORT_SYMBOL_FOR_KVM(kvm_exc_entry) > > /* > * int kvm_enter_guest(struct kvm_run *run, struct kvm_vcpu *vcpu) > @@ -215,6 +217,14 @@ SYM_FUNC_START(kvm_enter_guest) > /* Save host GPRs */ > kvm_save_host_gpr a2 > > + /* > + * The csr_era member variable of the pt_regs structure is required > + * for unwinding orc to perform stack traceback, so we need to put > + * pc into csr_era member variable here. > + */ > + pcaddi t0, 0 > + st.d t0, a2, PT_ERA Hi, Xianglai, It should use `SYM_CODE_START` to mark the `kvm_enter_guest` rather than `SYM_FUNC_START`, since the `SYM_FUNC_START` is used to mark "C-likely" asm functionw. I guess the kvm_enter_guest is something like exception handler becuase the last instruction is "ertn". So usually it should mark UNWIND_HINT_REGS where can find last frame info by "$sp". However, all info is store to "$a2", this mark should be   `UNWIND_HINT sp_reg=ORC_REG_A2(???) type=UNWIND_HINT_TYPE_REGS`. I don't konw why save this function internal PC here by `pcaddi t0, 0`, and I think it is no meaning(, for exception handler, they save last PC by read CSR.ERA). The `kvm_enter_guest` saves registers by "$a2"("$sp" - PT_REGS) beyond stack ("$sp"), it is dangerous if IE is enable. So I wonder if there is really a stacktrace through this function? Jinyang > + > addi.d a2, a1, KVM_VCPU_ARCH > st.d sp, a2, KVM_ARCH_HSP > st.d tp, a2, KVM_ARCH_HTP > @@ -225,7 +235,7 @@ SYM_FUNC_START(kvm_enter_guest) > csrwr a1, KVM_VCPU_KS > kvm_switch_to_guest > SYM_FUNC_END(kvm_enter_guest) > -EXPORT_SYMBOL(kvm_enter_guest) > +EXPORT_SYMBOL_FOR_KVM(kvm_enter_guest) > > SYM_FUNC_START(kvm_save_fpu) > fpu_save_csr a0 t1 > @@ -233,7 +243,7 @@ SYM_FUNC_START(kvm_save_fpu) > fpu_save_cc a0 t1 t2 > jr ra > SYM_FUNC_END(kvm_save_fpu) > -EXPORT_SYMBOL(kvm_save_fpu) > +EXPORT_SYMBOL_FOR_KVM(kvm_save_fpu) > > SYM_FUNC_START(kvm_restore_fpu) > fpu_restore_double a0 t1 > @@ -241,7 +251,7 @@ SYM_FUNC_START(kvm_restore_fpu) > fpu_restore_cc a0 t1 t2 > jr ra > SYM_FUNC_END(kvm_restore_fpu) > -EXPORT_SYMBOL(kvm_restore_fpu) > +EXPORT_SYMBOL_FOR_KVM(kvm_restore_fpu) > > #ifdef CONFIG_CPU_HAS_LSX > SYM_FUNC_START(kvm_save_lsx) > @@ -250,7 +260,7 @@ SYM_FUNC_START(kvm_save_lsx) > lsx_save_data a0 t1 > jr ra > SYM_FUNC_END(kvm_save_lsx) > -EXPORT_SYMBOL(kvm_save_lsx) > +EXPORT_SYMBOL_FOR_KVM(kvm_save_lsx) > > SYM_FUNC_START(kvm_restore_lsx) > lsx_restore_data a0 t1 > @@ -258,7 +268,7 @@ SYM_FUNC_START(kvm_restore_lsx) > fpu_restore_csr a0 t1 t2 > jr ra > SYM_FUNC_END(kvm_restore_lsx) > -EXPORT_SYMBOL(kvm_restore_lsx) > +EXPORT_SYMBOL_FOR_KVM(kvm_restore_lsx) > #endif > > #ifdef CONFIG_CPU_HAS_LASX > @@ -268,7 +278,7 @@ SYM_FUNC_START(kvm_save_lasx) > lasx_save_data a0 t1 > jr ra > SYM_FUNC_END(kvm_save_lasx) > -EXPORT_SYMBOL(kvm_save_lasx) > +EXPORT_SYMBOL_FOR_KVM(kvm_save_lasx) > > SYM_FUNC_START(kvm_restore_lasx) > lasx_restore_data a0 t1 > @@ -276,7 +286,7 @@ SYM_FUNC_START(kvm_restore_lasx) > fpu_restore_csr a0 t1 t2 > jr ra > SYM_FUNC_END(kvm_restore_lasx) > -EXPORT_SYMBOL(kvm_restore_lasx) > +EXPORT_SYMBOL_FOR_KVM(kvm_restore_lasx) > #endif > > #ifdef CONFIG_CPU_HAS_LBT