linux-kernel - Re: [PATCH V2 2/2] LoongArch: KVM: fix "unreliable stack" issue

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Message-ID: <e1f4b85e-0177-91b7-c422-22ed60607260@loongson.cn>
Date: Tue, 23 Dec 2025 09:25:08 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Xianglai Li <lixianglai@...ngson.cn>, loongarch@...ts.linux.dev,
 linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc: stable@...r.kernel.org, Huacai Chen <chenhuacai@...nel.org>,
 WANG Xuerui <kernel@...0n.name>, Tianrui Zhao <zhaotianrui@...ngson.cn>,
 Charlie Jenkins <charlie@...osinc.com>, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH V2 2/2] LoongArch: KVM: fix "unreliable stack" issue



On 2025/12/22 下午7:34, 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+0x100/0x1e0
> [<0>] kvm_arch_vcpu_ioctl_run+0x260/0x488 [kvm]
> [<0>] kvm_vcpu_ioctl+0x200/0xcd8 [kvm]
> [<0>] sys_ioctl+0x498/0xf00
> [<0>] do_syscall+0x94/0x190
> [<0>] handle_syscall+0xb8/0x158
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Xianglai Li <lixianglai@...ngson.cn>
> ---
> Cc: Huacai Chen <chenhuacai@...nel.org>
> Cc: WANG Xuerui <kernel@...0n.name>
> Cc: Tianrui Zhao <zhaotianrui@...ngson.cn>
> Cc: Bibo Mao <maobibo@...ngson.cn>
> Cc: Charlie Jenkins <charlie@...osinc.com>
> Cc: Xianglai Li <lixianglai@...ngson.cn>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> 
>   arch/loongarch/kvm/switch.S | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/arch/loongarch/kvm/switch.S b/arch/loongarch/kvm/switch.S
> index 93845ce53651..e3ecb24a3bc5 100644
> --- a/arch/loongarch/kvm/switch.S
> +++ b/arch/loongarch/kvm/switch.S
> @@ -170,6 +170,7 @@ 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
> @@ -214,6 +215,7 @@ SYM_FUNC_START(kvm_enter_guest)
>   	addi.d	a2, sp, -PT_SIZE
>   	/* Save host GPRs */
>   	kvm_save_host_gpr a2
> +	st.d	ra, a2, PT_ERA
Had better add some comments here to show that it is special for unwind 
usage since there is "st.d ra, a2, PT_R1" already in macro 
kvm_save_host_gpr().

Regards
Bibo Mao
>   
>   	addi.d	a2, a1, KVM_VCPU_ARCH
>   	st.d	sp, a2, KVM_ARCH_HSP
>