From: Jinyang He <hejinyang@loongson.cn>
To: Huacai Chen <chenhuacai@kernel.org>, lixianglai <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 20:06:36 +0800 [thread overview]
Message-ID: <259eb913-0667-a16a-f916-5bc9725037ae@loongson.cn> (raw)
In-Reply-To: <CAAhV-H43UxunddHJOnONmXNtJbk1vriiXjWk5XU7M9e8gKr+tg@mail.gmail.com>
On 2026-04-27 16:48, Huacai Chen wrote:
> 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.
Yes, I'd prefer SYM_CODE_START/SYM_CODE_END here.
From Documentation/core-api/asm-annotations.rst, SYM_FUNC_* is for
C-like functions with standard calling conventions, while SYM_CODE_* is
for special code with non-standard conventions (interrupt handlers,
entry/exception code, trampolines). The kvm_enter_guest is like a
trampoline which ertn to guest.
But if changing to SYM_CODE_* causes other issues with the current patch,
perhaps we can be flexible about this for now.
Thanks
Jinyang
>
> 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 12:06 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
2026-04-27 12:06 ` Jinyang He [this message]
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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