From: Huacai Chen <chenhuacai@kernel.org>
To: Xianglai Li <lixianglai@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 15:56:01 +0800 [thread overview]
Message-ID: <CAAhV-H6g41ah0xUxKJfe1=+xSMeaBcAbGnYya-xMAT3NtFUbgg@mail.gmail.com> (raw)
In-Reply-To: <20260414113111.2997864-2-lixianglai@loongson.cn>
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.
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 7:55 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 [this message]
2026-04-27 8:36 ` lixianglai
2026-04-27 8:48 ` Huacai Chen
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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