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

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Message-ID: <CAAhV-H4PehwGm-WwEuu4ZPbQutJR6m62tOSUxLcGQAxR_YX0Eg@mail.gmail.com>
Date: Tue, 23 Dec 2025 10:46:51 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Bibo Mao <maobibo@...ngson.cn>
Cc: Xianglai Li <lixianglai@...ngson.cn>, loongarch@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, stable@...r.kernel.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 Tue, Dec 23, 2025 at 9:27 AM Bibo Mao <maobibo@...ngson.cn> wrote:
>
>
>
> 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().
Then there is a new problem, why can unwinder not recognize the
instruction in  kvm_save_host_gpr()?

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