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Message-ID: <831f8f7e-1628-42e2-ca2e-7772ad9d3057@loongson.cn>
Date: Thu, 18 Dec 2025 19:05:04 +0800
From: lixianglai <lixianglai@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: 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>,
Bibo Mao <maobibo@...ngson.cn>, Charlie Jenkins <charlie@...osinc.com>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/2] LoongArch: KVM: Compile the switch.S file directly
into the kernel
Hi Huacai Chen:
> Hi, Xianglai,
>
> On Wed, Dec 17, 2025 at 11:49 AM Xianglai Li <lixianglai@...ngson.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.
>>
>> 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/Kbuild | 2 +-
>> arch/loongarch/include/asm/asm-prototypes.h | 16 ++++++++++
>> arch/loongarch/include/asm/kvm_host.h | 5 +--
>> arch/loongarch/include/asm/kvm_vcpu.h | 20 ++++++------
>> arch/loongarch/kvm/Makefile | 2 +-
>> arch/loongarch/kvm/main.c | 35 ++-------------------
>> arch/loongarch/kvm/switch.S | 22 ++++++++++---
>> 7 files changed, 49 insertions(+), 53 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..eb591276d191 100644
>> --- a/arch/loongarch/include/asm/asm-prototypes.h
>> +++ b/arch/loongarch/include/asm/asm-prototypes.h
>> @@ -20,3 +20,19 @@ asmlinkage void noinstr __no_stack_protector ret_from_kernel_thread(struct task_
>> struct pt_regs *regs,
>> int (*fn)(void *),
>> void *fn_arg);
>> +
>> +void kvm_exc_entry(void);
>> +int kvm_enter_guest(void *run, void *vcpu);
>> +
>> +#ifdef CONFIG_CPU_HAS_LSX
>> +void kvm_save_lsx(void *fpu);
>> +void kvm_restore_lsx(void *fpu);
>> +#endif
>> +
>> +#ifdef CONFIG_CPU_HAS_LASX
>> +void kvm_save_lasx(void *fpu);
>> +void kvm_restore_lasx(void *fpu);
>> +#endif
>> +
>> +void kvm_save_fpu(void *fpu);
>> +void kvm_restore_fpu(void *fpu);
>> diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
>> index e4fe5b8e8149..0aa7679536cc 100644
>> --- a/arch/loongarch/include/asm/kvm_host.h
>> +++ b/arch/loongarch/include/asm/kvm_host.h
>> @@ -85,7 +85,6 @@ 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
>> @@ -344,11 +343,9 @@ enum hrtimer_restart kvm_swtimer_wakeup(struct hrtimer *timer);
>> void kvm_arch_flush_remote_tlbs_memslot(struct kvm *kvm, const struct kvm_memory_slot *memslot);
>> void kvm_init_vmcs(struct kvm *kvm);
>> void kvm_exc_entry(void);
>> -int kvm_enter_guest(struct kvm_run *run, struct kvm_vcpu *vcpu);
>> +int kvm_enter_guest(void *run, void *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/include/asm/kvm_vcpu.h b/arch/loongarch/include/asm/kvm_vcpu.h
>> index 3784ab4ccdb5..8af98a3d7b0c 100644
>> --- a/arch/loongarch/include/asm/kvm_vcpu.h
>> +++ b/arch/loongarch/include/asm/kvm_vcpu.h
>> @@ -53,28 +53,28 @@ void kvm_deliver_exception(struct kvm_vcpu *vcpu);
>>
>> void kvm_own_fpu(struct kvm_vcpu *vcpu);
>> void kvm_lose_fpu(struct kvm_vcpu *vcpu);
>> -void kvm_save_fpu(struct loongarch_fpu *fpu);
>> -void kvm_restore_fpu(struct loongarch_fpu *fpu);
>> +void kvm_save_fpu(void *fpu);
>> +void kvm_restore_fpu(void *fpu);
> Why are these modifications needed?
In the assembly file switch.S, we used the macro definition
EXPORT_SYMBOL to export symbols without version information,
which led to an alarm during the compilation stage. In order to solve
this problem we need to put the symbol statement
in the file "arch/loongarch/include/asm/asm-prototypes.h", And function
declarations in the parameter types defined
in the header file "arch/loongarch/include/asm/kvm_host h", it is very
big, in order to reduce the
"arch/loongarch/include/asm/asm-prototypes.h" the contents of the file,
So we change the parameters in the function
declaration, then the function declaration directly into the file
"arch/loongarch/include/asm/asm-prototypes.h".
>
> Huacai
>
>> void kvm_restore_fcsr(struct loongarch_fpu *fpu);
>>
>> #ifdef CONFIG_CPU_HAS_LSX
>> int kvm_own_lsx(struct kvm_vcpu *vcpu);
>> -void kvm_save_lsx(struct loongarch_fpu *fpu);
>> -void kvm_restore_lsx(struct loongarch_fpu *fpu);
>> +void kvm_save_lsx(void *fpu);
>> +void kvm_restore_lsx(void *fpu);
>> #else
>> static inline int kvm_own_lsx(struct kvm_vcpu *vcpu) { return -EINVAL; }
>> -static inline void kvm_save_lsx(struct loongarch_fpu *fpu) { }
>> -static inline void kvm_restore_lsx(struct loongarch_fpu *fpu) { }
>> +static inline void kvm_save_lsx(void *fpu) { }
>> +static inline void kvm_restore_lsx(void *fpu) { }
>> #endif
>>
>> #ifdef CONFIG_CPU_HAS_LASX
>> int kvm_own_lasx(struct kvm_vcpu *vcpu);
>> -void kvm_save_lasx(struct loongarch_fpu *fpu);
>> -void kvm_restore_lasx(struct loongarch_fpu *fpu);
>> +void kvm_save_lasx(void *fpu);
>> +void kvm_restore_lasx(void *fpu);
>> #else
>> static inline int kvm_own_lasx(struct kvm_vcpu *vcpu) { return -EINVAL; }
>> -static inline void kvm_save_lasx(struct loongarch_fpu *fpu) { }
>> -static inline void kvm_restore_lasx(struct loongarch_fpu *fpu) { }
>> +static inline void kvm_save_lasx(void *fpu) { }
>> +static inline void kvm_restore_lasx(void *fpu) { }
>> #endif
>>
>> #ifdef CONFIG_CPU_HAS_LBT
>> 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 80ea63d465b8..67d234540ed4 100644
>> --- a/arch/loongarch/kvm/main.c
>> +++ b/arch/loongarch/kvm/main.c
>> @@ -340,8 +340,7 @@ 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);
>> @@ -357,30 +356,8 @@ 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;
>> @@ -414,16 +391,10 @@ 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..93845ce53651 100644
>> --- a/arch/loongarch/kvm/switch.S
>> +++ b/arch/loongarch/kvm/switch.S
>> @@ -5,6 +5,7 @@
>>
>> #include <linux/linkage.h>
>> #include <asm/asm.h>
>> +#include <asm/page.h>
>> #include <asm/asmmacro.h>
>> #include <asm/loongarch.h>
>> #include <asm/regdef.h>
>> @@ -100,10 +101,18 @@
>> * - 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
>> .cfi_sections .debug_frame
>> SYM_CODE_START(kvm_exc_entry)
>> + .p2align PAGE_SHIFT
>> UNWIND_HINT_UNDEFINED
>> csrwr a2, KVM_TEMP_KS
>> csrrd a2, KVM_VCPU_KS
>> @@ -190,8 +199,8 @@ 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(kvm_exc_entry)
>>
>> /*
>> * int kvm_enter_guest(struct kvm_run *run, struct kvm_vcpu *vcpu)
>> @@ -215,8 +224,8 @@ 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)
>> +EXPORT_SYMBOL(kvm_enter_guest)
>>
>> SYM_FUNC_START(kvm_save_fpu)
>> fpu_save_csr a0 t1
>> @@ -224,6 +233,7 @@ SYM_FUNC_START(kvm_save_fpu)
>> fpu_save_cc a0 t1 t2
>> jr ra
>> SYM_FUNC_END(kvm_save_fpu)
>> +EXPORT_SYMBOL(kvm_save_fpu)
>>
>> SYM_FUNC_START(kvm_restore_fpu)
>> fpu_restore_double a0 t1
>> @@ -231,6 +241,7 @@ SYM_FUNC_START(kvm_restore_fpu)
>> fpu_restore_cc a0 t1 t2
>> jr ra
>> SYM_FUNC_END(kvm_restore_fpu)
>> +EXPORT_SYMBOL(kvm_restore_fpu)
>>
>> #ifdef CONFIG_CPU_HAS_LSX
>> SYM_FUNC_START(kvm_save_lsx)
>> @@ -239,6 +250,7 @@ SYM_FUNC_START(kvm_save_lsx)
>> lsx_save_data a0 t1
>> jr ra
>> SYM_FUNC_END(kvm_save_lsx)
>> +EXPORT_SYMBOL(kvm_save_lsx)
>>
>> SYM_FUNC_START(kvm_restore_lsx)
>> lsx_restore_data a0 t1
>> @@ -246,6 +258,7 @@ SYM_FUNC_START(kvm_restore_lsx)
>> fpu_restore_csr a0 t1 t2
>> jr ra
>> SYM_FUNC_END(kvm_restore_lsx)
>> +EXPORT_SYMBOL(kvm_restore_lsx)
>> #endif
>>
>> #ifdef CONFIG_CPU_HAS_LASX
>> @@ -255,6 +268,7 @@ SYM_FUNC_START(kvm_save_lasx)
>> lasx_save_data a0 t1
>> jr ra
>> SYM_FUNC_END(kvm_save_lasx)
>> +EXPORT_SYMBOL(kvm_save_lasx)
>>
>> SYM_FUNC_START(kvm_restore_lasx)
>> lasx_restore_data a0 t1
>> @@ -262,10 +276,8 @@ SYM_FUNC_START(kvm_restore_lasx)
>> fpu_restore_csr a0 t1 t2
>> jr ra
>> SYM_FUNC_END(kvm_restore_lasx)
>> +EXPORT_SYMBOL(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
>>
>>
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