From: Huacai Chen <chenhuacai@kernel.org>
To: lixianglai <lixianglai@loongson.cn>, Jinyang He <hejinyang@loongson.cn>
Cc: loongarch@lists.linux.dev, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org, Tianrui Zhao <zhaotianrui@loongson.cn>,
Bibo Mao <maobibo@loongson.cn>
Subject: Re: [PATCH V4 1/2] LoongArch: KVM: Compile the switch.S file directly into the kernel
Date: Mon, 27 Apr 2026 16:48:47 +0800 [thread overview]
Message-ID: <CAAhV-H43UxunddHJOnONmXNtJbk1vriiXjWk5XU7M9e8gKr+tg@mail.gmail.com> (raw)
In-Reply-To: <3c07246f-75d2-f138-94c3-8a71f749f443@loongson.cn>
On Mon, Apr 27, 2026 at 4:43 PM lixianglai <lixianglai@loongson.cn> wrote:
>
> Hi Huacai Chen:
> > Hi, Xianglai,
> >
> > After this patch I get:
> > arch/loongarch/kvm/switch.o: warning: objtool: kvm_enter_guest+0x0:
> > unreachable instruction
> >
> > But if I restore SYM_FUNC_START/SYM_FUNC_END for kvm_enter_guest, the
> > warning disappear. So please make sure which one is correct.
> Oh~ Here, we should use SYM_FUNC_START/SYM_FUNC_END. I also reproduced
> this issue locally.
> After making the modification, the compilation did not notice this
> compilation warning.
Jinyang,
What's your opinion? I remember you suggest to use
SYM_CODE_START/SYM_CODE_END here.
Huacai
>
>
> Thanks,
> Xianglai.
>
> > Huacai
> >
> > On Tue, Apr 14, 2026 at 7:57 PM Xianglai Li <lixianglai@loongson.cn> wrote:
> >> If we directly compile the switch.S file into the kernel, the address of
> >> the kvm_exc_entry function will definitely be within the DMW memory area.
> >> Therefore, we will no longer need to perform a copy relocation of
> >> kvm_exc_entry.
> >>
> >> Based on the above description, compile switch.S directly into the kernel,
> >> and then remove the copy relocation execution logic for the kvm_exc_entry
> >> function.
> >>
> >> Signed-off-by: Xianglai Li <lixianglai@loongson.cn>
> >> ---
> >> Cc: Huacai Chen <chenhuacai@kernel.org>
> >> Cc: Tianrui Zhao <zhaotianrui@loongson.cn>
> >> Cc: Bibo Mao <maobibo@loongson.cn>
> >>
> >> arch/loongarch/Kbuild | 2 +-
> >> arch/loongarch/include/asm/asm-prototypes.h | 21 +++++++++++++
> >> arch/loongarch/include/asm/kvm_host.h | 3 --
> >> arch/loongarch/kvm/Makefile | 2 +-
> >> arch/loongarch/kvm/main.c | 35 ++-------------------
> >> arch/loongarch/kvm/switch.S | 27 +++++++++++-----
> >> 6 files changed, 46 insertions(+), 44 deletions(-)
> >>
> >> diff --git a/arch/loongarch/Kbuild b/arch/loongarch/Kbuild
> >> index beb8499dd8ed..1c7a0dbe5e72 100644
> >> --- a/arch/loongarch/Kbuild
> >> +++ b/arch/loongarch/Kbuild
> >> @@ -3,7 +3,7 @@ obj-y += mm/
> >> obj-y += net/
> >> obj-y += vdso/
> >>
> >> -obj-$(CONFIG_KVM) += kvm/
> >> +obj-$(subst m,y,$(CONFIG_KVM)) += kvm/
> >>
> >> # for cleaning
> >> subdir- += boot
> >> diff --git a/arch/loongarch/include/asm/asm-prototypes.h b/arch/loongarch/include/asm/asm-prototypes.h
> >> index 704066b4f736..e8ce153691e5 100644
> >> --- a/arch/loongarch/include/asm/asm-prototypes.h
> >> +++ b/arch/loongarch/include/asm/asm-prototypes.h
> >> @@ -20,3 +20,24 @@ asmlinkage void noinstr __no_stack_protector ret_from_kernel_thread(struct task_
> >> struct pt_regs *regs,
> >> int (*fn)(void *),
> >> void *fn_arg);
> >> +
> >> +struct kvm_run;
> >> +struct kvm_vcpu;
> >> +
> >> +void kvm_exc_entry(void);
> >> +int kvm_enter_guest(struct kvm_run *run, struct kvm_vcpu *vcpu);
> >> +
> >> +struct loongarch_fpu;
> >> +
> >> +#ifdef CONFIG_CPU_HAS_LSX
> >> +void kvm_save_lsx(struct loongarch_fpu *fpu);
> >> +void kvm_restore_lsx(struct loongarch_fpu *fpu);
> >> +#endif
> >> +
> >> +#ifdef CONFIG_CPU_HAS_LASX
> >> +void kvm_save_lasx(struct loongarch_fpu *fpu);
> >> +void kvm_restore_lasx(struct loongarch_fpu *fpu);
> >> +#endif
> >> +
> >> +void kvm_save_fpu(struct loongarch_fpu *fpu);
> >> +void kvm_restore_fpu(struct loongarch_fpu *fpu);
> >> diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
> >> index 19eb5e5c3984..0bcdffc14c5f 100644
> >> --- a/arch/loongarch/include/asm/kvm_host.h
> >> +++ b/arch/loongarch/include/asm/kvm_host.h
> >> @@ -86,7 +86,6 @@ struct kvm_context {
> >> struct kvm_world_switch {
> >> int (*exc_entry)(void);
> >> int (*enter_guest)(struct kvm_run *run, struct kvm_vcpu *vcpu);
> >> - unsigned long page_order;
> >> };
> >>
> >> #define MAX_PGTABLE_LEVELS 4
> >> @@ -356,8 +355,6 @@ void kvm_exc_entry(void);
> >> int kvm_enter_guest(struct kvm_run *run, struct kvm_vcpu *vcpu);
> >>
> >> extern unsigned long vpid_mask;
> >> -extern const unsigned long kvm_exception_size;
> >> -extern const unsigned long kvm_enter_guest_size;
> >> extern struct kvm_world_switch *kvm_loongarch_ops;
> >>
> >> #define SW_GCSR (1 << 0)
> >> diff --git a/arch/loongarch/kvm/Makefile b/arch/loongarch/kvm/Makefile
> >> index cb41d9265662..fe665054f824 100644
> >> --- a/arch/loongarch/kvm/Makefile
> >> +++ b/arch/loongarch/kvm/Makefile
> >> @@ -11,7 +11,7 @@ kvm-y += exit.o
> >> kvm-y += interrupt.o
> >> kvm-y += main.o
> >> kvm-y += mmu.o
> >> -kvm-y += switch.o
> >> +obj-y += switch.o
> >> kvm-y += timer.o
> >> kvm-y += tlb.o
> >> kvm-y += vcpu.o
> >> diff --git a/arch/loongarch/kvm/main.c b/arch/loongarch/kvm/main.c
> >> index 2c593ac7892f..18800a38b150 100644
> >> --- a/arch/loongarch/kvm/main.c
> >> +++ b/arch/loongarch/kvm/main.c
> >> @@ -348,8 +348,7 @@ void kvm_arch_disable_virtualization_cpu(void)
> >>
> >> static int kvm_loongarch_env_init(void)
> >> {
> >> - int cpu, order, ret;
> >> - void *addr;
> >> + int cpu, ret;
> >> struct kvm_context *context;
> >>
> >> vmcs = alloc_percpu(struct kvm_context);
> >> @@ -365,30 +364,8 @@ static int kvm_loongarch_env_init(void)
> >> return -ENOMEM;
> >> }
> >>
> >> - /*
> >> - * PGD register is shared between root kernel and kvm hypervisor.
> >> - * So world switch entry should be in DMW area rather than TLB area
> >> - * to avoid page fault reenter.
> >> - *
> >> - * In future if hardware pagetable walking is supported, we won't
> >> - * need to copy world switch code to DMW area.
> >> - */
> >> - order = get_order(kvm_exception_size + kvm_enter_guest_size);
> >> - addr = (void *)__get_free_pages(GFP_KERNEL, order);
> >> - if (!addr) {
> >> - free_percpu(vmcs);
> >> - vmcs = NULL;
> >> - kfree(kvm_loongarch_ops);
> >> - kvm_loongarch_ops = NULL;
> >> - return -ENOMEM;
> >> - }
> >> -
> >> - memcpy(addr, kvm_exc_entry, kvm_exception_size);
> >> - memcpy(addr + kvm_exception_size, kvm_enter_guest, kvm_enter_guest_size);
> >> - flush_icache_range((unsigned long)addr, (unsigned long)addr + kvm_exception_size + kvm_enter_guest_size);
> >> - kvm_loongarch_ops->exc_entry = addr;
> >> - kvm_loongarch_ops->enter_guest = addr + kvm_exception_size;
> >> - kvm_loongarch_ops->page_order = order;
> >> + kvm_loongarch_ops->exc_entry = (void *)kvm_exc_entry;
> >> + kvm_loongarch_ops->enter_guest = (void *)kvm_enter_guest;
> >>
> >> vpid_mask = read_csr_gstat();
> >> vpid_mask = (vpid_mask & CSR_GSTAT_GIDBIT) >> CSR_GSTAT_GIDBIT_SHIFT;
> >> @@ -422,16 +399,10 @@ static int kvm_loongarch_env_init(void)
> >>
> >> static void kvm_loongarch_env_exit(void)
> >> {
> >> - unsigned long addr;
> >> -
> >> if (vmcs)
> >> free_percpu(vmcs);
> >>
> >> if (kvm_loongarch_ops) {
> >> - if (kvm_loongarch_ops->exc_entry) {
> >> - addr = (unsigned long)kvm_loongarch_ops->exc_entry;
> >> - free_pages(addr, kvm_loongarch_ops->page_order);
> >> - }
> >> kfree(kvm_loongarch_ops);
> >> }
> >>
> >> diff --git a/arch/loongarch/kvm/switch.S b/arch/loongarch/kvm/switch.S
> >> index f1768b7a6194..1a5636790ef9 100644
> >> --- a/arch/loongarch/kvm/switch.S
> >> +++ b/arch/loongarch/kvm/switch.S
> >> @@ -5,10 +5,12 @@
> >>
> >> #include <linux/linkage.h>
> >> #include <asm/asm.h>
> >> +#include <asm/page.h>
> >> #include <asm/asmmacro.h>
> >> #include <asm/loongarch.h>
> >> #include <asm/regdef.h>
> >> #include <asm/unwind_hints.h>
> >> +#include <linux/kvm_types.h>
> >>
> >> #define HGPR_OFFSET(x) (PT_R0 + 8*x)
> >> #define GGPR_OFFSET(x) (KVM_ARCH_GGPR + 8*x)
> >> @@ -100,8 +102,16 @@
> >> * - is still in guest mode, such as pgd table/vmid registers etc,
> >> * - will fix with hw page walk enabled in future
> >> * load kvm_vcpu from reserved CSR KVM_VCPU_KS, and save a2 to KVM_TEMP_KS
> >> + *
> >> + * PGD register is shared between root kernel and kvm hypervisor.
> >> + * So world switch entry should be in DMW area rather than TLB area
> >> + * to avoid page fault reenter.
> >> + *
> >> + * In future if hardware pagetable walking is supported, we won't
> >> + * need to copy world switch code to DMW area.
> >> */
> >> .text
> >> + .p2align PAGE_SHIFT
> >> .cfi_sections .debug_frame
> >> SYM_CODE_START(kvm_exc_entry)
> >> UNWIND_HINT_UNDEFINED
> >> @@ -190,8 +200,8 @@ ret_to_host:
> >> kvm_restore_host_gpr a2
> >> jr ra
> >>
> >> -SYM_INNER_LABEL(kvm_exc_entry_end, SYM_L_LOCAL)
> >> SYM_CODE_END(kvm_exc_entry)
> >> +EXPORT_SYMBOL_FOR_KVM(kvm_exc_entry)
> >>
> >> /*
> >> * int kvm_enter_guest(struct kvm_run *run, struct kvm_vcpu *vcpu)
> >> @@ -200,7 +210,7 @@ SYM_CODE_END(kvm_exc_entry)
> >> * a0: kvm_run* run
> >> * a1: kvm_vcpu* vcpu
> >> */
> >> -SYM_FUNC_START(kvm_enter_guest)
> >> +SYM_CODE_START(kvm_enter_guest)
> >> /* Allocate space in stack bottom */
> >> addi.d a2, sp, -PT_SIZE
> >> /* Save host GPRs */
> >> @@ -215,8 +225,8 @@ SYM_FUNC_START(kvm_enter_guest)
> >> /* Save kvm_vcpu to kscratch */
> >> csrwr a1, KVM_VCPU_KS
> >> kvm_switch_to_guest
> >> -SYM_INNER_LABEL(kvm_enter_guest_end, SYM_L_LOCAL)
> >> -SYM_FUNC_END(kvm_enter_guest)
> >> +SYM_CODE_END(kvm_enter_guest)
> >> +EXPORT_SYMBOL_FOR_KVM(kvm_enter_guest)
> >>
> >> SYM_FUNC_START(kvm_save_fpu)
> >> fpu_save_csr a0 t1
> >> @@ -224,6 +234,7 @@ SYM_FUNC_START(kvm_save_fpu)
> >> fpu_save_cc a0 t1 t2
> >> jr ra
> >> SYM_FUNC_END(kvm_save_fpu)
> >> +EXPORT_SYMBOL_FOR_KVM(kvm_save_fpu)
> >>
> >> SYM_FUNC_START(kvm_restore_fpu)
> >> fpu_restore_double a0 t1
> >> @@ -231,6 +242,7 @@ SYM_FUNC_START(kvm_restore_fpu)
> >> fpu_restore_cc a0 t1 t2
> >> jr ra
> >> SYM_FUNC_END(kvm_restore_fpu)
> >> +EXPORT_SYMBOL_FOR_KVM(kvm_restore_fpu)
> >>
> >> #ifdef CONFIG_CPU_HAS_LSX
> >> SYM_FUNC_START(kvm_save_lsx)
> >> @@ -239,6 +251,7 @@ SYM_FUNC_START(kvm_save_lsx)
> >> lsx_save_data a0 t1
> >> jr ra
> >> SYM_FUNC_END(kvm_save_lsx)
> >> +EXPORT_SYMBOL_FOR_KVM(kvm_save_lsx)
> >>
> >> SYM_FUNC_START(kvm_restore_lsx)
> >> lsx_restore_data a0 t1
> >> @@ -246,6 +259,7 @@ SYM_FUNC_START(kvm_restore_lsx)
> >> fpu_restore_csr a0 t1 t2
> >> jr ra
> >> SYM_FUNC_END(kvm_restore_lsx)
> >> +EXPORT_SYMBOL_FOR_KVM(kvm_restore_lsx)
> >> #endif
> >>
> >> #ifdef CONFIG_CPU_HAS_LASX
> >> @@ -255,6 +269,7 @@ SYM_FUNC_START(kvm_save_lasx)
> >> lasx_save_data a0 t1
> >> jr ra
> >> SYM_FUNC_END(kvm_save_lasx)
> >> +EXPORT_SYMBOL_FOR_KVM(kvm_save_lasx)
> >>
> >> SYM_FUNC_START(kvm_restore_lasx)
> >> lasx_restore_data a0 t1
> >> @@ -262,10 +277,8 @@ SYM_FUNC_START(kvm_restore_lasx)
> >> fpu_restore_csr a0 t1 t2
> >> jr ra
> >> SYM_FUNC_END(kvm_restore_lasx)
> >> +EXPORT_SYMBOL_FOR_KVM(kvm_restore_lasx)
> >> #endif
> >> - .section ".rodata"
> >> -SYM_DATA(kvm_exception_size, .quad kvm_exc_entry_end - kvm_exc_entry)
> >> -SYM_DATA(kvm_enter_guest_size, .quad kvm_enter_guest_end - kvm_enter_guest)
> >>
> >> #ifdef CONFIG_CPU_HAS_LBT
> >> STACK_FRAME_NON_STANDARD kvm_restore_fpu
> >> --
> >> 2.39.1
> >>
>
>
next prev parent reply other threads:[~2026-04-27 8:48 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-14 11:31 [PATCH V4 0/2] LoongArch: KVM: fix "unreliable stack" issue Xianglai Li
2026-04-14 11:31 ` [PATCH V4 1/2] LoongArch: KVM: Compile the switch.S file directly into the kernel Xianglai Li
2026-04-27 7:56 ` Huacai Chen
2026-04-27 8:36 ` lixianglai
2026-04-27 8:48 ` Huacai Chen [this message]
2026-04-27 12:06 ` Jinyang He
2026-04-29 9:47 ` Huacai Chen
2026-04-14 11:31 ` [PATCH V4 2/2] LoongArch: KVM: fix "unreliable stack" issue Xianglai Li
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