From: lixianglai <lixianglai@loongson.cn>
To: Huacai Chen <chenhuacai@kernel.org>
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 16:36:10 +0800 [thread overview]
Message-ID: <3c07246f-75d2-f138-94c3-8a71f749f443@loongson.cn> (raw)
In-Reply-To: <CAAhV-H6g41ah0xUxKJfe1=+xSMeaBcAbGnYya-xMAT3NtFUbgg@mail.gmail.com>
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.
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 8:43 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 [this message]
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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